Thyroid Function Tests

Thyroid Function Tests 

Definition

Thyroid function tests are blood tests used to evaluate how effectively the thyroid gland is working. These tests include the thyroid-stimulating hormone test (TSH), the thyroxine test (T4), the triiodothyronine test (T3), the thyroxine-binding globulin test (TBG), the triiodothyronine resin uptake test (T3RU), and the long-acting thyroid stimulator test (LATS).

Purpose

Thyroid function tests are used to:

• help diagnose an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism)
• evaluate thyroid gland activity
• monitor response to thyroid therapy

Precautions

Thyroid treatment must be stopped one month before blood is drawn for a thyroxine (T4) test.

Steroids, propranolol (Inderal), cholestyramine (Questran), and other medications that may influence thyroid activity are usually stopped before a triiodothyronine (T3) test.

Estrogens, anabolic steroids, phenytoin, and thyroid medications may be discontinued prior to a thyroxine-binding globulin (TBG) test. The laboratory analyzing the blood sample must be told if the patient cannot stop taking any of these medications. Some patients will be told to take these medications as usual so that the doctor can determine how they affect thyroxine-binding globulin.

Patients are asked not to take estrogens, androgens, phenytoin (Dilantin), salicylates, and thyroid medications before having a triiodothyronine resin uptake (T3RU) test.

Prior to taking a long-acting thyroid stimulant (LATS) test, the patient will probably be told to stop taking all drugs that could affect test results.

Description

Most doctors consider the sensitive thyroid-stimulating hormone (TSH) test to be the most accurate measure of thyroid activity. By measuring the level of TSH, doctors can determine even small problems in thyroid activity. Because this test is sensitive, abnormalities in thyroid function can be determined before a patient complains of symptoms.

TSH "tells" the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). Before TSH tests were used, standard blood tests measured levels of T4 and T3 to determine if the thyroid gland was working properly. The triiodothyrine (T3) test measures the amount of this hormone in the blood. T3 is normally present in very small amounts, but has a significant impact on metabolism. It is the active component of thyroid hormone.

The thyroxine-binding globulin (TBG) test measures blood levels of this substance, which is manufactured in the liver. TBG binds to T3 and T4, prevents the kidneys from flushing the hormones from the blood, and releases them when and where they are needed to regulate body functions.

The triiodothyronine resin uptake (T3RU) test measures blood T4 levels. Laboratory analysis of this test takes several days, and it is used less often than tests whose results are available more quickly.

The long-acting thyroid stimulator (LATS) test shows whether blood contains long-acting thyroid stimulator. Not normally present in blood, LATS causes the thyroid to produce and secrete abnormally high amounts of hormones.

It takes only minutes for a nurse or medical technician to collect the blood needed for these blood tests. A needle is inserted into a vein, usually in the forearm, and a small amount of blood is collected and sent to a laboratory for testing. The patient will usually feel minor discomfort from the "stick" of the needle.

Preparation

There is no need to make any changes in diet or activities. The patient may be asked to stop taking certain medications until after the test is performed.

Aftercare

Warm compresses can be used to relieve swelling or discomfort at the site of the puncture. With a doctor's approval, the patient may start taking medications stopped before the test.

Normal results

Not all laboratories measure or record thyroid hormone levels the same way. Each laboratory will provide a range of values that are considered normal for each test. Some acceptable ranges are listed below.

Tsh

Normal TSH levels for adults are 0.5-5.0 mU/L.

T4

Normal T4 levels are:

• 10.1-2.0 ug/dl at birth
• 7.5-16.5 ug/dl at one to four months
• 5.5-14.5 ug/dl at four to 12 months
• 5.6-12.6 ug/dl at one to six years
• 4.9-11.7 ug/dl at 10 years
• 4-11 ug/dl at 10 years and older.

Levels of free T4 (thyroxine not attached to TBG) are higher in teenagers than in adults.

Normal T4 levels do not necessarily indicate normal thyroid function. T4 levels can register within normal ranges in a patient who:

• is pregnant
• has recently had contrast x rays
• has nephrosis or cirrhosis

T3

Normal T3 levels are:

• 90-170 ng/dl at birth
• 115-190 ng/dl at six to 12 years
• 110-230 ng/dl in adulthood

Tbg

Normal TBG levels are:

• 1.5-3.4 mg/dl or 15-34 mg/L in adults
• 2.9-5.4 mg/dl or 29-54 mg/L in children.

T3ru

Between 25% and 35% of T3 should bind to or be absorbed by the resin added to the blood sample. The test indirectly measures the amount of thyroid binding globulin (TBG) and thyroid-binding prealbumin (TBPA) in the blood.

Lats

Long-acting thyroid stimulator is found in the blood of only 5% of healthy people.

Abnormal results

T4

Elevated T4 levels can be caused by:

• acute thyroiditis
• birth control pills

• clofibrate (Altromed-S)
• contrast x rays using iodine
• estrogen therapy
• heparin
• heroin
• hyperthyroidism
• pregnancy
• thyrotoxicosis
• toxic thyroid adenoma

Cirrhosis and severe non-thyroid disease can raise T4 levels slightly.

Reduced T4 levels can be caused by:

• anabolic steroids
• androgens
• antithyroid drugs
• cretinism
• hypothyroidism
• kidney failure
• lithium (Lithane, Lithonate)
• myxedema
• phenytoin
• propranolol

T3

Although T3 levels usually rise and fall when T4 levels do, T3 toxicosis causes T3 levels to rise while T4 levels remain normal. T3 toxicosis is a complication of:

• Graves' disease
• toxic adenoma
• toxic nodular goiter

T3 levels normally rise when a woman is pregnant or using birth-control pills. Elevated T3 levels can also occur in patients who use estrogen or methadone or who have:

• certain genetic disorders that do not involve thyroid malfunction
• hyperthyroidism
• thyroiditis
• t3 thyrotoxicosis
• toxic adenoma

Low T3 levels may be a symptom of:

• acute or chronic illness
• hypothyroidism
• kidney or liver disease
• starvation

Decreased T3 levels can also be caused by using:

• anabolic steroids
• androgens
• phenytoin
• propranolol
• reserpine (Serpasil)
• salicylates in high doses

Tbg

TBG levels, normally high during pregnancy, are also high in newborns. Elevated TBG levels can also be symptoms of:

• acute hepatitis
• acute intermittent porphyria
• hypothyroidism
• inherited thyroid hormone abnormality

TBG levels can also become high by using:

• anabolic steroids
• birth control pills
• anti-thyroid agents
• clofibrate
• estrogen therapy
• phenytoin
• salicylates in high doses
• thiazides
• thyroid medications
• warfarin (Coumadin)

TBG levels can be raised or lowered by inherited liver disease whose cause is unknown.

Low TBG levels can be a symptom of:

• acromegaly
• acute hepatitis or other acute illness
• hyperthyroidism
• kidney disease
• malnutrition
• marked hypoproteinemia
• uncompensated acidosis

Key terms

Acidosis — A condition in which blood and tissues are unusually acidic.

Acromegaly — A disorder in which growth hormone (a chemical released from the pituitary gland in the brain) causes increased growth in bone and soft tissue. Patients have enlarged hands, feet, noses, and ears, as well as a variety of other disturbances throughout the body.

Acute intermittent porphyria — An inherited disease affecting the liver and bone marrow. The liver overproduces a specific acid and the disease is characterized by attacks of high blood pressure, abdominal colic, psychosis, and nervous system disorders.

Anabolic steroids — Protein-building compounds used to treat certain anemias and cancers, strengthen bones, and stimulate weight gain and growth. Anabolic steroids are sometimes used to illegally enhance athletic performance.

Cholestyramine (Questran) — A drug used to bind with bile acids and prevent their reabsorption and to stimulate fat absorption.

Cirrhosis — Progressive disease of the liver, associated with failure in liver cell functioning and blood flow in the liver. Tissue and cells are damaged, the liver becomes fibrous, and jaundice can result.

Clofibrate (Altromed-S) — Medication used to lower levels of blood cholesterol and triglycerides.

Cretinism — Severe hypothyroidism that is present at birth and characterized by severe mental retardation.

Graves' disease — The most common form of hyperthyroidism, characterized by bulging eyes, rapid heart rate, and other symptoms.

Heparin — An organic acid that occurs naturally in the body and prevents blood clots. Heparin is also made synthetically and can be given as a treatment when required.

Hepatitis — Inflammation of the liver.

Hyperthyroidism — Overactive thyroid gland; symptoms include irritability/nervousness, muscle weakness, tremors, irregular menstrual periods, weight loss, sleep problems, thyroid enlargement, heat sensitivity, and vision/eye problems. The most common type of this disorder is called Graves' disease.

Hypoproteinemia — Abnormally low levels of protein in the blood.

Hypothyroidism — Underactive thyroid gland; symptoms include fatigue, difficulty swallowing, mood swings, hoarse voice, sensitivity to cold, forgetfulness, and dry/coarse skin and hair.

Lithium (Lithane, Lithromate) — Medication prescribed to treat manic (excited) phases of bipolar disorder.

Myxedema — Hypothyroidism, characterized by thick, puffy features, an enlarged tongue, and lack of emotion.

Nephrosis — Any degenerative disease of the kidney (not to be confused with nephritis, an inflammation of the kidney due to bacteria).

Nodular goiter — An enlargement of the thyroid (goiter) caused when groups of cells collect to form nodules.

Phenytoin (Dilantin) — Anti-convulsive medication used to treat seizure disorders.

Propranolol (Inderal) — Medication commonly prescribed to treat high blood pressure; is a beta-adrenergic blocker and can also be used to treat irregular heartbeat, heart attack, migraine, and tremors.

Reserpine (Serpasil) — A drug prescribed for high blood pressure.

Salicylates — Aspirin and certain other nonsteroidal anti-inflammatory drugs (NSAIDs).

Thiazides — A group of drugs used to increase urine output.

Thyroid gland — A butterfly-shaped gland in front and to the sides of the upper part of the windpipe; influences body processes like growth, development, reproduction, and metabolism.

Thyroiditis — Inflammation of the thyroid gland.

Thyrotoxicosis — A condition resulting from high levels of thyroid hormones in the blood.

Toxic thyroid adenoma — Self-contained concentrations of thyroid tissue that may produce excessive amounts of thyroid hormone.

T3ru

A high degree of resin uptake and high thyroxine levels indicate hyperthyroidism. A low degree of resin uptake, coupled with low thyroxine levels, is a symptom of hypothyroidism.

Thyroxine and triiodothyronine resin uptake that are not both high or low may be a symptom of a thyroxine-binding abnormality.

Lats

Long-acting thyroid stimulator, not usually found in blood, is present in the blood of 80% of patients with Graves' disease. It is a symptom of this disease whether or not symptoms of hyperthyroidism are detected.

Resources

Organizations

American Thyroid Association, Inc. Montefiore Medical Center, 111 E. 210th St., Bronx, NY 10467. http://www.thyroid.org.

Thyroid Foundation of America, Inc. Ruth Sleeper Hall, RSL350, 40 Parkman St., Boston, MA 02114-2698. (800) 832-8321. 〈http://www.tfaeweb.org/pub/tfa〉.

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test(s),

n a clinical or laboratory procedure designed to evaluate constituents or functions of the body.

test, acetone,

n See test, ketone bodies.

test, ACTH-stimulation (Thorn's test),

n a test of adrenocortical reserve based on changes in the eosinophil count and urinary levels of 17-ketosteroids and 17-hydroxycorticoids as a result of intravenous infusion or intramuscular injection of ACTH.

test, allergy, intradermal,

n a test for allergy performed by injecting a preparation containing the suspected allergen into the dermis.

test, amylase

n a determination of serum amylase, which is useful in the diagnosis of acute pancreatitis and after operations in which the pancreas might have been injured. The Somogyi sarcogenic method is often used, and the results are given in
Somogyi units, defined as the amount of amylase needed to digest 1.5 g of starch in 8 minutes at 37°C. The normal range is 60 to 200 units/100 ml. The serum amylase is also elevated in mumps and other diseases of the salivary glands.

test, amyloid

n See test, Congo red.

test, antiviral antibody,

n antibody tests in viral diseases. Included are complement-fixation tests for poliomyelitis, psittacosis, and Coxsackie infections; hemagglutination-inhibition tests for mumps, influenza, and encephalitides; and neutralization tests.

test, Aschheim-Zondek

n.pr See test, pregnancy.

test, ascorbic acid, intradermal,

n a test for ascorbic acid deficiency based on the decoloration of an intradermal injection of a purple dye (2,6-dichlorphenol-indophenol). Normally with a wheal of 4 mm, using a dye concentration of N/300, decoloration occurs in 10 to 15 minutes.

test, basophilic aggregation

n a test for lead poisoning based on increased stippling of erythrocytes. More than 2% stippled cells are seen in lead poisoning. See also test, lead.

test, Bell's palsy,

n.pr simple clinical tests, such as motor function tests, in which the patient is asked to whistle, pucker the lips, smile, or wrinkle the forehead; also sensory function tests in which the patient is asked to taste sweet with sugar, sour with citric acid, bitter with quinine, and salt with sodium chloride.

test, Benedict's,

n a nonspecific copper reduction test for glucose in the urine. Cupric sulfate in the Benedict's reagent is reduced by glucose during the reaction to cuprous oxide, a reddish-orange precipitate.

test, bilirubin

n qualitative, presumptive, quantitative, or specific determinations for bilirubin in the urine and blood serum. Included are Gmelin's test and van den Bergh's test.

test, bleeding time,

n techniques for determining the time interval required for hemostasis to occur after a standardized wound has been made in the capillary bed. See also test, Duke's and test, Ivy's.

test, Brinell hardness

n.pr a means of determining surface hardness by measuring the amount of resistance to the indentation of a steel ball. Recorded as the Brinell hardness number (BHN); the higher the number, the harder the material. Generally indicative of abrasion resistance.

test, Bromsulphalein (BSP)

n a test of liver function based on the removal of a known quantity of Bromsulphalein from the blood in a measured period of time. Normal values are less than 5% retention at the end of 45 minutes with an intravenous dose of 5 mg/kg body weight. It is a useful test of hepatocellular disease and detoxifying ability but is not applicable in the presence of extrahepatic or intrahepatic obstructive jaundice.

test, Bunnell,

n.pr See test, Paul-Bunnell.

test, capillary resistance (Rumpel-Leede-Hess test, Gothlin's test),

n a test of capillary fragility based on the number of petechiae that develop when a standardized intraluminal positive pressure is applied to the capillaries either by a blood pressure cuff or a suction cup applied to the skin. See also test, tourniquet.

test, caries activity,

n a test used to predict the probability of developing new or increased decay; may include assessments of saliva and plaque for the presence of certain designated microorganisms or studies of salivary secretion and sugar clearance.

test, CO capacity (CO combining power test),

n a general measure of the alkalinity or acidity of the blood. Various normal adult ranges are given (e.g., 23 to 30 mEq/L of serum or 55 to 70 vol/100 ml of serum). A low value is found in diabetic acidosis, hyperventilation, certain kidney diseases, and severe diarrhea. A high value is found in excessive administration of ACTH or cortisone, intake of sodium bicarbonate, and persistent vomiting.

test, CO combining power,

n See test, CO₂ capacity.

test, cold bends,

n a mechanical test used for assessing ductility.

test, colorimetric caries susceptibility (Snyder's test),

n a method of determining the concentration of acid-producing bacteria in the saliva by use of bromcresol green in a culture medium. The reliability of this and other salivary bacterial tests for dental caries susceptibility is questionable.

test, Congo red,

n.pr a test for amyloidosis based on the more rapid disappearance (excess of 60% injected dye in 1 hour) of Congo red from the serum of affected patients than from that of normal individuals. Gingival biopsy and positive staining with methyl violet or crystal violet also indicate amyloidosis.

test, creatinine clearance

n a renal function test of exogenous creatinine clearance. It is a convenient clinical test of glomerular filtration rate. It is calculated as the quotient of the product of urine creatinine (mg/L) and urine volume (L/24 hr) divided by the serum creatinine concentration (mg/L). The normal value for young healthy adults of average size (1.73 M² body surface area) is 115 to 155 L/24 hr (±15%).

test, dermal,

n See test, skin.

test, Dick's (scarlet fever test),

n a skin test to determine susceptibility or immunity to scarlet fever. A positive test is indicated when an area of erythema and edema measuring more than 10 mm in diameter occurs 8 to 24 hours after an intradermal injection of a standardized erythrogenic toxin.

test, Duke's,

n.pr a test of bleeding time as indicated by the time that elapses before a puncture wound of the earlobe ceases to bleed. Normal range is 2 to 4½ minutes.

test, electric,

n a test to determine whether a pulp is vital.

test, erythrocyte sedimentation

n a macroscopic test of the blood used to detect certain pathologic conditions, particularly inflammation. The blood cells are allowed to settle in the presence of an anticoagulant and the time (sedimentation time) determined. The greater the time or rate, the more severe the condition. Pregnancy and menstruation affect the sedimentation.

test, flow,

n used in the ADA specification for dental amalgam; measured as the percentage shortening of a cylinder of the material.

test, fluorescent treponemal antibody, absorbed (FTA-APS)

n a modification of the original FTA test for syphilis that employs a protein preparation from the Reiter treponeme.

test for trigeminal nerve function,

n.pl three simple clinical tests for trigeminal nerve function: (1)
sensation: apply gentle touch, pinpricks, or warm or cold objects to areas supplied by the nerve and note responses; (2)
reflex: try the jaw jerk and eye and sneeze reflexes; (3)
motor function: test the patient's ability to chew and work against resistance and observe contraction of the masseter and temporal muscles by visual examination and digital palpation.

test, Foshay's,

n.pr a skin test for tularemia using the Foshay antigen.

test, Friedman's

n.pr See test, pregnancy.

test, glare,

n an examination of blade sharpness using a magnifying glass under light, which reveals dull edges as round, shiny, reflective surfaces.

test, glucose paper,

n a test in which paper is impregnated with glucose oxidase and other reagents (TesTape, Clinistix). When the paper is moistened with fresh urine, the presence of glucose will cause a change in the color of the paper.

test, glucose tolerance (GTT),

n a test for abnormalities of carbohydrate tolerance by glucose loading and subsequent serial measurements of the concentration of glucose in the blood. Graphic representation of the concentration and the elapsed time makes up the glucose tolerance curve. Abnormal curves occur in diabetes mellitus, thyrotoxicosis, Cushing syndrome, acromegaly, and pheochromocytoma.

test, Gothlin's,

n.pr See test, capillary resistance.

test, hardness,

n See hardness, Mohs; test, Brinell hardness; test, Knoop hardness; and test, Vickers hardness.

test, Hess's,

n.pr See test, capillary resistance.

test, histoplasmin

n a skin test to determine sensitization to
Histoplasma capsulatum. A positive test indicates past or present infection (histoplasmosis).

test, infectious mononucleosis,

n one of several tests for the diagnosis of infectious mononucleosis (e.g., Paul-Bunnell test).

test, intracutaneous,

n See test, skin.

test, intradermal,

n See test, skin.

test, Ivy's,

n.pr a test of bleeding time performed by making a standard wound and touching the blood with filter paper every 30 seconds until no blood appears on the paper. Normal range is 3 to 7 minutes.

test, Janet's,

n.pr a test to differentiate between functional and organic anesthesia. With the eyes closed, patients are instructed to say “yes” or “no” as they feel or do not feel the examiner's touch. In functional anesthesia, they will say “no,” whereas in organic anesthesia, they will say nothing.

test, ketone bodies (acetone test, Rothera's test)

n nitroprusside reaction tests for acetone and acetoacetic acid and the ferric chloride test for acetoacetic acid. Commercially prepared nitroprusside test tablets (Acetest) and powder (Acetone Test Denco) are available.

test, Kline's,

n.pr a flocculation test for syphilis based on the combination of the cardiolipin antigen with reagin to form grossly visible aggregates.

test, Knoop hardness,

n.pr a means of measuring surface hardness by resistance to the penetration of an indenting tool made of diamond. Produces an indentation that has a diamond or rhombic shape. Especially preferred for testing hardness of tooth structure.

test, laboratory,

n investigative procedures performed in the laboratory that are useful in the diagnosis of disease, including biopsy examination of tissue specimens, determination of type and characteristics of associated microorganisms, serology, blood and urine chemistry, hemogram (red cell count, hemoglobin content, white cell count, differential white cell count), and metabolic studies (basal metabolic rate).

test, LE,

n a test for lupus erythematosus based on the presence of a single (or multiple) homogenous basophilic inclusion(s) in polymorphonuclear leukocytes. Such LE cells have also been found in cases of rheumatoid arthritis, allergic reactions to penicillin, hydralazine toxicity, and “lupoid cirrhosis.” Thus the test is not definitive for lupus only; it is one of the diagnostic tests for causation.

test, lead,

n a test used to detect clinical lead poisoning or exposure to lead (e.g., coproporphyrinuria test, trace element analysis, urinary lead content test, and basophilic aggregation test).

test, Leede's,

n.pr See test, capillary resistance.

test, Mann-Whitney U,

n.pr a powerful nonparametric statistic test of significance between two means with unequal sample sizes.

test, Mantoux

n.pr an intracutaneous tuberculin test using either old tuberculin (OT) or purified protein derivative (PPD). A positive reaction read 24 and 48 hours after injection shows erythema and edema greater than 5 mm in diameter and indicates past or present tuberculosis.

test, Mazzini's

n.pr a flocculation test for syphilis.

test, Mohs,

n.pr See hardness, Mohs.

test, nontreponemal antigen,

n.pl serologic tests for syphilis using nontreponemal antigens. Such tests are not absolutely specific or sensitive for syphilis. Included are the Kline, Kahn, and Kolmer tests, and the VDRL slide test.

test, one-stage,

n See time, prothrombin.

test, oral glucose tolerance test (OGTT),

n the application of glucose to the body, typically administered orally, in order to determine the rate at which glucose is metabolized. Can be used to diagnose diabetes mellitus.

test, patch,

n (percutaneous test), a test for allergies that is performed by placing the suspected allergen in direct contact with the skin or mucosa. See also test, skin.

test, Paul-Bunnell,

n.pr a test for infectious mononucleosis based on increased agglutination of sheep red blood cells resulting from heterophil antibodies in the serum. The test is considered positive if dilution of serum of 1:80 or higher agglutinates the sheep cells. Elevated agglutinin titers are more likely to be found during the second or third week of the disease, but the serum may not become positive until 7 weeks have elapsed.

test, percussion,

n a method of examination executed by striking the tissues of the area being examined with the fingers or an instrument, listening for resulting sounds, and observing the response of the patient.

test, percutaneous

n See test, patch.

test, Phelan's

n.pr a common test for diagnosing carpal tunnel syndrome. In a positive Phelan's test, tingling or numbness is felt within one minute when the subject's hands are held with the wrists flexed (usually at a 90° angle).

test, phenolsulfonphthalein (PSP)

n a renal test that roughly estimates glomerular function by measuring the rate of excretion of the dye after intravenous injection. Normally, after 15 minutes, 25% or more of the dye should be excreted in the urine.

test, plasma ketone

n a test using nitroprusside for the detection of high levels of ketone bodies in the blood. The test is read 0 to 4 plus. A strongly positive reaction is seen in diabetic ketoacidosis.

test, prothrombin consumption (serum prothrombin time),

n a convenient screening test of the first stage of blood coagulation as determined by the quantity of prothrombin remaining after coagulation. The test reflects the formation of plasma thromboplastin, provided the one-stage prothrombin time of plasma is normal. See also time, prothrombin.

test, pulp,

n a diagnostic test to determine clinical pulp vitality and/or abnormality.

test, Reiter protein complement-fixation (RPCF)

n.pr treponemal antigen test for syphilis using extracts from the nonpathogenic Reiter treponeme.

test, reverse torque (RTT) (tork),

n a test used to determine the degree of osseointegration of an implant by applying a rotational force in the opposite direction originally used to set the implant into the bone; in essence, it measures the shear strength at the point where the implant meets the bone.

test, Rockwell,

n an indentation test for hardness of a material. A static load is placed on a steel ball or diamond point, and the depth of the indentation is measured on the instrument. The depth of the indentation is remeasured after the load is increased. The hardness number is related to the type of point used and to the depth of the indentation.

test, Rothera's,

n.pr See test, ketone bodies.

test, routine,

n a test or group of tests performed on most or all patients to detect relatively common disorders or to establish a base for further evaluation of a patient.

test, Rumpel-Leede-Hess,

n.pr See test, capillary resistance.

test, scarlet fever,

n See test, Dick's.

test, Schick,

n.pr a skin test to demonstrate the presence or absence of an immunity to diphtheria.

test, scratch (skin test),

n a test for allergies performed by placing a preparation containing the allergen on the skin and scratching the skin. A positive reaction is indicated by the formation of a wheal and flare.

test, serologic

n test of blood serum for the diagnosis of infectious diseases.

test, Snyder's,

n.pr See test, colorimetric caries susceptibility.

test, sterilizer,

n the periodic use of spore strip, color strip, or other microbial test to ensure that a sterilizer (autoclave, oven) is killing all microbes predictably.

test strip,

n a blood test used to check blood sugar levels in diabetics. The patient places a drop of blood on the strip, and the strip changes color according to the level of blood sugar present.

test, subcutaneous,

n See test, skin.

test, syphilis,

n a serologic test for syphilis based on the presence of a reagin, appearing during the second or third week of infec-tion. Included are the Hinton, Kahn, Kline, Mazzini, Wassermann, and
Treponema pallidum immobilization tests.

test, tension,

n an evaluation used to determine the presence or absence of attached gingiva within the oral cavity. The tongue, cheek, and lip are retracted to apply pressure at the mucogingival junction and make the alveolar mucosa taut.

test, thermal,

n the use of heat or cold as an aid in diagnosis (e.g., the use of heat or cold in testing the pulp).

test, Thorn's,

n.pr See test, ACTH-stimulation.

test, thromboplastin generation

n a test of the integrity of the first stage of blood coagulation and the nature of the defect. A patient's serum, plasma, or platelets are substituted in a system that is complete except for one of the factors to be tested for (antihemophilic factor, plasma thromboplastin antecedent, plasma thromboplastin component, or platelets), and the rate of thromboplastin generation is determined.

test, tourniquet

n a test for capillary fragility based on counting petechiae in a given area of the arm after application of the rubber cuff of a sphygmomanometer for 15 minutes.

test, transillumination,

n a test for a pulpless tooth in which the use of transmitted light shows a shadow of the root when the pulp is necrotic or has been replaced by a filling (not always reliable).

test, Treponema pallidum immobilization (TPI)

n a test to confirm syphilis by demonstrating the immobilization of
Treponema pallidum by specific antibodies in the serum of an infected individual; not widely used.

test, tuberculin,

n a test for past or present infection with tubercle bacilli. See also test, Mantoux.

test, tuberculin skin

n an intradermal injection of old tuberculin (OT) or purified protein derivative (PPD) to determine a specific sensitivity or susceptibility to tuberculosis.

test, tularemia,

n See test, Foshay's.

test, U, Mann-Whitney,

n.pr See test, Mann-Whitney U.

test, urea clearance,

n a clinical test of renal function determined by the clearance of urea from the plasma by the kidney each minute. Average normal value is 75 ml/min (75% to 125% of normal).

test, urine, routine,

n the routine examination of the urine, including amount, appearance, pH level, specific gravity, qualitative tests for sugar and protein, and microscopic examination of sediment.

test, van den Bergh's,

n.pr a test of hepatic function by measuring serum conjugated (“direct-reacting”) 1-minute bilirubin, total serum bilirubin, and, by difference, unconjugated (indirect) bilirubin. Obstructive jaundice and hemolytic jaundice give abnormal values.

test, VDRL (Venereal Disease Research Laboratory),

n.pr a serologic nontreponemal antigen test for the detection of syphilitic reagin by means of a reaction between the reagin and a standard antigen.

test, Vickers hardness,

n.pr a penetration type of hardness test using a square-based pyramid made of diamond.

test, vitality,

n the procedure using thermal, electrical, or mechanical stimuli to determine the response of the pulp in a tooth.

test, Wassermann,

n.pr a complement-fixation test for syphilis.

test, Zondek's,

n.pr See test, pregnancy.

tests, liver function,

n.pl tests to measure the severity of liver disease, aid in the differential diagnosis of the various types of disease of the hepatobiliary system, and follow the course of liver disease. Screening tests include urine bile, urine urobilinogen, Bromsulphalein (BSP) excretion, serum transaminases, thymol turbidity, cephalin-cholesterol flocculation, and van den Bergh's reaction (1 minute direct and total).

tests, pancreatic function,

n.pl tests of enzyme levels in blood and urine (amylase, lipase), fecal fat content, trypsin activity, nitrogen content, alteration of digestive capacity, and alteration of pancreatic secretion via duodenal intubation.

tests, pregnancy (Aschheim-Zondek test, Friedman's test),

n.pl biologic or chemical tests that determine pregnancy. The tests are usually based on changes in the ovaries of an animal injected with the urine of a pregnant woman. Included are the Aschheim-Zondek test (using mice or rats) and the Friedman test (using virgin rabbits). Male frogs and female and male toads are also used. A saliva test has also been used.

tests, pulmonary function,

n.pl tests used to evaluate respiratory function (e.g., tests of vital capacity, tidal volume, maximal breathing capacity, timed vital capacity, arterial blood gases).

tests, rapid reagin,

n.pl serologic tests for syphilis that permit rapid and economic screening in the field. Included are the rapid plasma reagin (RPR) test and the unheated serum reagin (USR) test.

tests, renal function,

n.pl quantitative tests including inulin or mannitol clearance for the glomerular filtration rate (GFR), paraaminohippurate (PAH) clearance for renal plasma flow, and the maximum rate of tubular excretion of paraaminohippurate and of reabsorption of glucose for the measurement of excretory and reabsorptive functions of the renal tubules. Clinical renal tests are used to assess the extent of renal impairment. They include blood urea nitrogen (BUN), nonprotein nitrogen (NPN), urea clearance, endogenous creatinine clearance, filtration fraction, phenolsulfonphthalein (PSP), and concentration tests.

tests, screening,

n.pl a group of tests especially chosen to detect specific abnormalities.

tests, skin,

n.pl tests to determine the sensitivity or susceptibility to infections by a specific agent, the presence of an allergy, or the presence of a nutritional deficiency. Included are the Mantoux, Schick, Dick, Frei, histoplasmin, and Foshay tests for infectious diseases (tests in which allergens are placed onto or into the skin) and the intradermal ascorbic acid, dermal, intradermal (intracutaneous), patch (percutaneous), scratch, and subcutaneous tests.

tests, thyroid function,

n.pl tests for thyroid function (e.g., radioactive iodine uptake, protein-bound iodine, basal metabolic rate, serum cholesterol, triiodothyronine suppression, thyroid-stimulating hormone tests).

tests, transaminase

n.pl tests for serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT). The normal value for serum glutamic oxaloacetic transaminase is 40 units or less; that for serum glutamic pyruvic transaminase is 35 units or less. The serum glutamic oxaloacetic transaminase value in myocardial infarction is 3 to 20 times the normal.

tests, treponemal antigen,

n.pl tests for syphilis using
Treponema pallidum or extracts from a treponeme as antigen. Included are
T. pallidum immobilization (TPI),
T. pallidum agglutination (TPA), fluorescent treponemal antibody (FTA), Reiter protein complement-fixation (RPCF), and
T. pallidum complement-fixation (TPCF) tests.

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thyroid

1. resembling a shield.

2. the thyroid gland (see below) secreting thyroid hormones (see below).

3. a pharmaceutical preparation of cleaned, dried, powdered thyroid gland, obtained from those domesticated animals used for food by humans.

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accessory thyroid

an additional thyroid located anywhere from the larynx to diaphragm, e.g. intrapericordial aorta; may be sufficient to supply the patient's need of thyroid hormone. Most common in dogs.

thyroid C cell

see c cell.

thyroid cartilage

the shield-shaped cartilage of the larynx.

thyroid diverticulum

primordium of the thyroid gland; appears as an outgrowth of the foregut between the first two pharyngeal pouches. This tube of epithelial cells grows ventrally into mesenchyme; the tube becomes the thyroglossal duct, the tip divides into two lobes, the thyroid glands.

thyroid dysfunction

see hypothyroidism, hyperthyroidism.

ectopic thyroid

migration of thyroid diverticulum tissue to aberrant sites occurs, e.g. thyroid tissue in the thymus. These cause no apparent abnormality.

thyroid extract

a pharmaceutical substance derived from thyroid glands, used in the treatment of hypothyroidism. See thyroid (3) (above).

thyroid function tests

used to assess the functional capacity of the thyroid glands; most commonly employed in dogs and cats. Include plasma T₄, plasma T₃, free T₄ radioiodine uptake, and TSH response tests.

thyroid gland

the largest of the endocrine glands, situated in the neck caudal to the larynx. It produces hormones (see below) that are vital in maintaining normal growth and metabolism. It also serves as a storehouse for iodine.

Microscopic appearance of the thyroid gland. By permission from Guyton R, Hall JE, Textbook of Medical Physiology, Saunders, 2000

thyroid hormones

iodothyronines secreted by the thyroid gland, principally thyroxine (tetraiodothyronine, T₄) and tri-iodothyronine (T₃); derived from iodination of tyrosyl residues in thyroglobulin. The pharmaceutical names for T₄ and T₃ are levothyroxine and liothyronine, respectively. Regulate basal metabolic rate.

thyroid parafollicular cell

see c cell.

thyroid radioiodine uptake

used as a thyroid function test but superseded these days by estimates of T₄ (thyroxine).

thyroid-stimulating hormone (TSH)

see thyrotropin.

thyroid tumor

mostly follicular adenomas in old-aged dogs, cats and horses; papillary adenomas are rare.