Calcium, Blood

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Calcium, Blood

Synonym/acronym: Total calcium, Ca.

Common use

To investigate various conditions related to abnormally increased or decreased calcium levels.


Serum (1 mL) collected in a red- or red/gray-top tube. Plasma (1 mL) collected in a green-top (heparin) tube is also acceptable.

Normal findings

(Method: Spectrophotometry)
AgeConventional UnitsSI Units (Conventional Units × 0.25)
Cord8.2–11.2 mg/dL2.1–2.8 mmol/L
0–10 days7.6–10.4 mg/dL1.9–2.6 mmol/L
11 days–2 yr9–11 mg/dL2.2–2.8 mmol/L
3–12 yr8.8–10.8 mg/dL2.2–2.7 mmol/L
13–18 yr8.4–10.2 mg/dL2.1–2.6 mmol/L
Adult8.2–10.2 mg/dL2.1–2.6 mmol/L
Adult older than 90 yr8.2–9.6 mg/dL2.1–2.4 mmol/L


Calcium, the most abundant cation in the body, participates in almost all of the body’s vital processes. Calcium concentration is largely regulated by the parathyroid glands and by the action of vitamin D. Of the body’s calcium reserves, 98% to 99% is stored in the teeth and skeleton. Calcium values are higher in children because of growth and active bone formation. About 45% of the total amount of blood calcium circulates as free ions that participate in numerous regulatory functions to include bone development and maintenance, blood coagulation, transmission of nerve impulses, activation of enzymes, stimulating the glandular secretion of hormones, and control of skeletal and cardiac muscle contractility. The remaining calcium is bound to circulating proteins (40% bound mostly to albumin) and anions (15% bound to anions such as bicarbonate, citrate, phosphate, and lactate) and plays no physiological role. Calcium values can be adjusted up or down by 0.8 mg/dL for every 1 g/dL that albumin is greater than or less than 4 g/dL. Calcium and phosphorus levels are inversely proportional.

Fluid and electrolyte imbalances are often seen in patients with serious illness or injury; in these clinical situations, the normal homeostatic balance of the body is altered. During surgery or in the case of a critical illness, bicarbonate, phosphate, and lactate concentrations can change dramatically. Therapeutic treatments may also cause or contribute to electrolyte imbalance. This is why total calcium values can sometimes be misleading. Abnormal calcium levels are used to indicate general malfunctions in various body systems. Ionized calcium is used in more specific conditions (see monograph titled “Calcium, Ionized”).

Calcium values should be interpreted in conjunction with results of other tests. Normal calcium with an abnormal phosphorus value indicates impaired calcium absorption (possibly because of altered parathyroid hormone level or activity). Normal calcium with an elevated urea nitrogen value indicates possible hyperparathyroidism (primary or secondary). Normal calcium with decreased albumin value is an indication of hypercalcemia (high calcium levels). The most common cause of hypocalcemia (low calcium levels) is hypoalbuminemia. The most common causes of hypercalcemia are hyperparathyroidism and cancer (with or without bone metastases).

This procedure is contraindicated for



  • Detect parathyroid gland loss after thyroid or other neck surgery, as indicated by decreased levels
  • Evaluate cardiac arrhythmias and coagulation disorders to determine if altered serum calcium level is contributing to the problem
  • Evaluate the effects of various disorders on calcium metabolism, especially diseases involving bone
  • Monitor the effectiveness of therapy being administered to correct abnormal calcium levels, especially calcium deficiencies
  • Monitor the effects of renal failure and various drugs on calcium levels

Potential diagnosis

Increased in

  • Acidosis (related to imbalance in electrolytes; longstanding acidosis can result in osteoporosis and release of calcium into circulation)
  • Acromegaly (related to alteration in vitamin D metabolism, resulting in increased calcium)
  • Addison’s disease (related to adrenal gland dysfunction; decreased blood volume and dehydration occur in the absence of aldosterone)
  • Cancers (bone, Burkitt’s lymphoma, Hodgkin’s lymphoma, leukemia, myeloma, and metastases from other organs)
  • Dehydration (related to a decrease in the fluid portion of blood, causing an overall increase in the concentration of most plasma constituents)
  • Hyperparathyroidism (related to increased parathyroid hormone [PTH] and vitamin D levels, which increase circulating calcium levels)
  • Idiopathic hypercalcemia of infancy
  • Lung disease (tuberculosis, histoplasmosis, coccidioidomycosis, berylliosis) (related to activity by macrophages in the epithelium that interfere with vitamin D regulation by converting it to its active form; vitamin D increases circulating calcium levels)
  • Malignant disease without bone involvement (some cancers [e.g., squamous cell carcinoma of the lung and kidney cancer] produce PTH-related peptide that increases calcium levels)
  • Milk-alkali syndrome (Burnett’s syndrome) (related to excessive intake of calcium-containing milk or antacids, which can increase calcium levels)
  • Paget’s disease (related to calcium released from bone)
  • Pheochromocytoma (hyperparathyroidism related to multiple endocrine neoplasia type 2A [MEN2A] syndrome associated with some pheochromocytomas; PTH increases calcium levels)
  • Polycythemia vera (related to dehydration; decreased blood volume due to excessive production of red blood cells)
  • Renal transplant (related to imbalances in electrolytes; a common post-transplant issue)
  • Sarcoidosis (related to activity by macrophages in the granulomas that interfere with vitamin D regulation by converting it to its active form; vitamin D increases circulating calcium levels)
  • Thyrotoxicosis (related to increased bone turnover and release of calcium into the blood)
  • Vitamin D toxicity (vitamin D increases circulating calcium levels)

Decreased in

    Acute pancreatitis (complication of pancreatitis related to hypoalbuminemia and calcium binding by excessive fats) Alcoholism (related to insufficient nutrition) Alkalosis (increased blood pH causes intracellular uptake of calcium to increase) Chronic renal failure (related to decreased synthesis of vitamin D) Cystinosis (hereditary disorder of the renal tubules that results in excessive calcium loss) Hepatic cirrhosis (related to impaired metabolism of vitamin D and calcium) Hyperphosphatemia (phosphorus and calcium have an inverse relationship) Hypoalbuminemia (related to insufficient levels of albumin, an important carrier protein) Hypomagnesemia (lack of magnesium inhibits PTH and thereby decreases calcium levels) Hypoparathyroidism (congenital, idiopathic, surgical) (related to lack of PTH) Inadequate nutrition Leprosy (related to increased bone retention) Long-term anticonvulsant therapy (these medications block calcium channels and interfere with calcium transport) Malabsorption (celiac disease, tropical sprue, pancreatic insufficiency) (related to insufficient absorption) Massive blood transfusion (related to the presence of citrate preservative in blood product that chelates or binds calcium and removes it from circulation) Neonatal prematurity Osteomalacia (advanced) (bone loss is so advanced there is little calcium remaining to be released into circulation) Renal tubular disease (related to decreased synthesis of vitamin D) Vitamin D deficiency (rickets) (related to insufficient amounts of vitamin D, resulting in decreased calcium metabolism)

Critical findings

  • Less than 7 mg/dL (SI: Less than 1.8 mmol/L)
  • Greater than 12 mg/dL (SI: Greater than 3 mmol/L) (some patients can tolerate higher concentrations)
  • Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

  • Observe the patient for symptoms of critically decreased or elevated calcium levels. Hypocalcemia is evidenced by convulsions, arrhythmias, changes in electrocardiogram (ECG) in the form of prolonged ST segment and Q-T interval, facial spasms (positive Chvostek’s sign), tetany, lethargy, muscle cramps, numbness in extremities, tingling, and muscle twitching (positive Trousseau’s sign). Possible interventions include seizure precautions, increased frequency of ECG monitoring, and administration of calcium or magnesium.

  • Severe hypercalcemia is manifested by excessive thirst, polyuria, constipation, changes in ECG ( shortened QT interval due to shortening of the ST segment and prolonged PR interval), lethargy, confusion, muscle weakness, joint aches, apathy, anorexia, headache, nausea, vomiting, and ultimately may result in coma. Possible interventions include the administration of normal saline and diuretics to speed up dilution and excretion or administration of calcitonin or steroids to force the circulating calcium into the cells.

Interfering factors

  • Drugs that may increase calcium levels include anabolic steroids, some antacids, calcitriol, calcium salts, danazol, diuretics (long-term), ergocalciferol, isotretinoin, lithium, oral contraceptives, parathyroid extract, parathyroid hormone, prednisone, progesterone, tamoxifen, vitamin A, and vitamin D.
  • Drugs that may decrease calcium levels include albuterol, alprostadil, aminoglycosides, anticonvulsants, calcitonin, diuretics (initially), gastrin, glucagon, glucocorticoids, glucose, insulin, laxatives (excessive use), magnesium salts, methicillin, phosphates, plicamycin, sodium sulfate (given IV), tetracycline (in pregnancy), trazodone, and viomycin.
  • Calcium exhibits diurnal variation; serial samples should be collected at the same time of day for comparison.
  • Venous hemostasis caused by prolonged use of a tourniquet during venipuncture can falsely elevate calcium levels.
  • Patients on ethylenediaminetetra-acetic acid (EDTA) therapy (chelation) may show falsely decreased calcium values.
  • Hemolysis and icterus cause false-positive results because of interference from biological pigments.
  • Specimens should never be collected above an IV line because of the potential for dilution when the specimen and the IV solution combine in the collection container, falsely decreasing the result. There is also the potential of contaminating the sample with the substance of interest if it is present in the IV solution, falsely increasing the result.

Nursing Implications and Procedure

Potential nursing problems

Pain (Related to organ inflammation and surrounding tissues; excessive alcohol intake; infection; bone deformity)Emotional symptoms of distress; crying; agitation; facial grimace; moaning; verbalization of pain; rocking motions; irritability; disturbed sleep; diaphoresis; altered blood pressure and heart rate; nausea; vomiting; self-report of pain Collaborate with the patient and physician to identify the best pain management modality to provide relief; refrain from activities that may aggravate pain; use the application of heat or cold to the best effect in managing the pain; monitor pain severity
Health management (Related to failure to regulate diet; lack of exercise; alcohol use; smoking)Inability or failure to recognize or process information toward improving health and preventing illness with associated mental and physical effectsEncourage regular participation in weight—bearing exercise; assess diet, smoking, and alcohol use; teach the importance of adequate calcium intake with diet and supplements; refer to smoking cessation and alcohol treatment programs; collaborate with physician for bone density evaluation
Nutrition (Related to inability to digest foods, metabolize foods, ingest foods; refusal to eat; increased metabolic needs associated with disease process; lack of understanding; inability to obtain healthy foods)Unintended weight loss; current weight 20% below ideal weight; pale, dry skin; dry mucous membranes; documented inadequate caloric intake; subcutaneous tissue loss; hair pulls out easily; paresthesis Obtain accurate daily weight at the same time each day with the same scale; obtain an accurate nutritional history; assess attitude toward eating; promote a dietary consult to evaluate current eating habits and best method of nutritional supplementation; develop short-term and long-term eating strategies; monitor nutritional laboratory values such as albumin, transferrin, red blood cells (RBC), white blood cells (WBC), and serum electrolytes; discourage caffeinated and carbonated beverages; assess swallowing ability; encourage cultural home foods; provide a pleasant environment for eating; alter food seasoning to enhance flavor; provide parenteral or enteral nutrition as prescribed
Injury risk (Related to phosphorous retention; bone resorption; inadequate calcium resorption; acute or chronic renal failure; lack of dietary vitamin D; decreased sun exposure; eating disorders)Tingling sensation in the fingertips and around the mouth; muscle cramps; tetany; seizures; bone pain; weakness; unsteady gait; laryngospasm; cardiac dysrhythmias; hyperactive tendon reflexes Assess for signs and symptoms of hypocalcemia; monitor calcium and phosphorus levels; provide medication replacement therapy as prescribed; assess for bone pain; assess for alterations in mobility; increase the calcium in the diet; encourage the minimum recommended sun exposure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist as a general indicator in diagnosing health concerns.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s cardiovascular, gastrointestinal, genitourinary, hematopoietic, hepatobiliary, and musculoskeletal systems, as well as results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Recognize anxiety related to test results, and assess the patient for signs and symptoms of calcium imbalance. Teach the patient the signs and symptoms associated with a calcium imbalance. Assess associated studies such as ECG, phosphorus, and albumin so the correct therapeutic measures can be taken. Hypoalbuminemia may initiate symptoms of hypocalcemia in the presence of near-normal calcium levels.
  • Nutritional Considerations: Patients with abnormal calcium values should be informed that daily intake of calcium is important even though body stores in the bones can be called on to supplement circulating levels. Dietary calcium can be obtained from animal or plant sources. Milk and milk products, sardines, clams, oysters, salmon, rhubarb, spinach, beet greens, broccoli, kale, tofu, legumes, and fortified orange juice are high in calcium. Milk and milk products also contain vitamin D and lactose, which assist calcium absorption. Cooked vegetables yield more absorbable calcium than raw vegetables. Patients should be informed of the substances that can inhibit calcium absorption by irreversibly binding to some of the calcium, making it unavailable for absorption, such as oxalates, which naturally occur in some vegetables (e.g., beet greens, collards, leeks, okra, parsley, quinoa, spinach, Swiss chard) and are found in tea; phytic acid, found in some cereals (e.g., wheat bran, wheat germ); phosphoric acid, found in dark cola; and insoluble dietary fiber (in excessive amounts). Excessive protein intake can also negatively affect calcium absorption, especially if it is combined with foods high in phosphorus and in the presence of a reduced dietary calcium intake.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
  • Patient Education

    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
    • Answer any questions or address any concerns voiced by the patient or family.
    • Educate the patient regarding access to nutritional counseling services.
    • Provide contact information, if desired, for the Institute of Medicine of the National Academies (
    • Teach the patient and family the importance of adequate dietary calcium intake to maintain health.
    • Teach the patient that good oral hygiene prior to eating can improve the food’s flavor.
  • Expected Patient Outcomes

    • Knowledge
    • Validates that eating in a pleasant environment with companionship can enhance the appetite
    • States that parenteral or enteral nutrition may be used if oral intake is insufficient to support caloric needs
    • Skills
    • Performs an accurate daily self-weight and records the results correctly
    • Accurately self-administers prescribed dietary supplements
    • Attitude
    • Complies with the request to take prescribed calcium replacement therapy
    • Arranges consultation with the speech therapist to evaluate swallowing ability

Related Monographs

  • Related tests include ACTH, albumin, aldosterone, ALP, biopsy bone marrow, BMD, bone scan, calcitonin, calcium ionized, urine calcium, calculus kidney stone analysis, catecholamines, chloride, collagen cross-linked telopeptides, CBC, CT pelvis, CT spine, cortisol, CK and isoenzymes, DHEA, fecal fat, glucose, HVA, magnesium, metanephrines, osteocalcin, PTH, phosphorus, potassium, protein total, radiography bone, renin, sodium, thyroid scan, thyroxine, US abdomen, US thyroid and parathyroid, UA, and vitamin D.
  • Refer to the Cardiovascular, Gastrointestinal, Genitourinary, Hematopoietic, Hepatobiliary, and Musculoskeletal systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners
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