Vitamins A, B1, B6, and C

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Vitamins A, B1, B6, and C

Synonym/acronym: Vitamin A: retinol, carotene; vitamin B1: thiamine; vitamin B6: pyroxidine, P-5′-P, pyridoxyl-5-phosphate; vitamin C: ascorbic acid.

Common use

To assess vitamin deficiency or toxicity to assist in diagnosing nutritional disorders such as malabsorption; disorders that affect vision, skin, and bones; and other diseases.


Serum (1 mL) collected in a red-top tube each for vitamins A and C; plasma (1 mL) collected in a lavender-top (EDTA) tube each for vitamins B1 and B6.

Normal findings

(Method: High-performance liquid chromatography)
VitaminAgeConventional UnitsSI Units
Vitamin A(Conventional Units × 0.0349)
Birth–1 yr14–52 mcg/dL0.49–1.81 micromol/L
1–6 yr20–43 mcg/dL0.7–1.5 micromol/L
7–12 yr26–49 mcg/dL0.91–1.71 micromol/L
13–19 yr26–72 mcg/dL0.91–2.51 micromol/L
Adult30–120 mcg/dL1.05–4.19 micromol/L
Vitamin B1(Conventional Units × 29.6)
0.21–0.43 mcg/dL6.2–12.7 micromol/L
Vitamin B6(Conversion Factor × 4.046)
5–30 ng/mL20–121 nmol/L
Vitamin C(Conventional Units × 56.78)
0.6–1.9 mg/dL34.1–107.9 micromol/L
Vitamin B1, vitamin B6, and vitamin C levels tend to decrease in older adults.


Vitamin assays are used in the measurement of nutritional status. Low levels indicate inadequate oral intake, poor nutritional status, or malabsorption problems. High levels indicate excessive intake, vitamin intoxication, or absorption problems. Vitamin A is a fat-soluble nutrient that promotes normal vision and prevents night blindness; contributes to growth of bone, teeth, and soft tissues; supports thyroxine formation; maintains epithelial cell membranes, skin, and mucous membranes; and acts as an anti-infection agent. Vitamins B1, B6, and C are water soluble. Vitamin B1 acts as an enzyme and plays an important role in the Krebs cycle of cellular metabolism. Vitamin B6 is important in heme synthesis and functions as a coenzyme in amino acid metabolism and glycogenolysis. It includes pyridoxine, pyridoxal, and pyridoxamine. Vitamin C promotes collagen synthesis, maintains capillary strength, facilitates release of iron from ferritin to form hemoglobin, and functions in the stress response.

This procedure is contraindicated for



    Vitamin A

  • Assist in the diagnosis of night blindness
  • Evaluate skin disorders
  • Investigate suspected vitamin A deficiency
  • Vitamin B1

  • Investigate suspected beriberi
  • Monitor the effects of chronic alcoholism
  • Vitamin B6

  • Investigate suspected malabsorption or malnutrition
  • Investigate suspected vitamin B6 deficiency
  • Vitamin C

  • Investigate suspected metabolic or malabsorptive disorders
  • Investigate suspected scurvy

Potential diagnosis

Increased in

  • Vitamin A:
    • Chronic kidney disease
    • Idiopathic hypercalcemia in infants
    • Vitamin A toxicity

Decreased in

    Vitamin A:
    • Abetalipoproteinemia (related to poor absorption)
    • Carcinoid syndrome (related to poor absorption)
    • Chronic infections (vitamin A deficiency decreases ability to fight infection)
    • Cystic fibrosis (related to poor absorption)
    • Disseminated tuberculosis (related to poor absorption)
    • Hypothyroidism (condition decreases ability of beta carotene to convert to vitamin A)
    • Infantile blindness (related to dietary deficiency)
    • Liver, gastrointestinal (GI), or pancreatic disease (related to malabsorption or poor absorption)
    • Night blindness (related to chronic dietary deficiency or lack of absorption)
    • Protein malnutrition (related to dietary deficiency)
    • Sterility and teratogenesis (related to dietary deficiency)
    • Zinc deficiency (zinc is required for generation of vitamin A transport proteins)
    Vitamin B1:
    • Alcoholism (related to dietary deficiency)
    • Carcinoid syndrome (related to dietary deficiency or lack of absorption)
    • Hartnup’s disease (related to dietary deficiency)
    • Pellagra (related to dietary deficiency)
    Vitamin B6(this vitamin is involved in many essential functions, such as nucleic acid synthesis, enzyme activation, antibody production, electrolyte balance, and RBC formation; deficiencies result in a variety of conditions):
    • Alcoholism (related to dietary deficiency)
    • Asthma
    • Carpal tunnel syndrome
    • Gestational diabetes
    • Lactation (related to dietary deficiency and/or increased demand)
    • Malabsorption
    • Malnutrition
    • Neonatal seizures
    • Normal pregnancies (related to dietary deficiency and/or increased demand)
    • Occupational exposure to hydrazine compounds (enzymatic pathways are altered by hydralazines in a manner that increases excretion of vitamin B6)
    • Pellagra (related to dietary deficiency)
    • Pre-eclamptic edema
    • Renal dialysis
    • Uremia
    Vitamin C:
    • Alcoholism (related to dietary deficiency)
    • Anemia (related to dietary deficiency)
    • Cancer (related to dietary deficiency or lack of absorption)
    • Hemodialysis (vitamin C is lost during the treatment)
    • Hyperthyroidism (related to dietary deficiency and/or increased demand)
    • Malabsorption
    • Pregnancy (related to dietary deficiency and/or increased demand)
    • Rheumatoid disease
    • Scurvy (related to dietary deficiency or lack of absorption)

Critical findings

  • 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.

  • Vitamin toxicity can be as significant as problems brought about by vitamin deficiencies. The potential for toxicity is especially important to consider with respect to fat-soluble vitamins (A, D, E, and K), which are not eliminated from the body as quickly as water-soluble vitamins and can accumulate in the body. Most cases of toxicity are brought about by oversupplementing and can be avoided by consulting a qualified nutritionist for recommended daily dietary and supplemental allowances. Signs and symptoms of vitamin A toxicity may include headache, blurred vision, bone pain, joint pain, dry skin, and loss of appetite.

Interfering factors

  • Drugs and substances that may increase vitamin A levels include alcohol (moderate intake), oral contraceptives, and probucol.
  • Drugs and substances that may decrease vitamin A levels include alcohol (chronic intake, alcoholism), allopurinol, cholestyramine, colestipol, mineral oil, and neomycin.
  • Drugs that may decrease vitamin B1 levels include glibenclamide, isoniazid, and valproic acid.
  • Drugs that may decrease vitamin B6 levels include amiodarone, anticonvulsants, cycloserine, disulfiram, ethanol, hydralazine, isoniazid, levodopa, oral contraceptives, penicillamine, pyrazinoic acid, and theophylline.
  • Drugs and substances that may decrease vitamin C levels include acetylsalicylic acid, aminopyrine, barbiturates, estrogens, heavy metals, oral contraceptives, nitrosamines, and paraldehyde.
  • Chronic tobacco smoking decreases vitamin C levels.
  • Various diseases may affect vitamin levels (see Potential Diagnosis section).
  • Diets high in freshwater fish and tea, which are thiamine antagonists, may cause decreased vitamin B1 levels.
  • Long-term hyperalimentation may result in decreased vitamin levels.
  • Exposure of the specimen to light decreases vitamin levels, resulting in a falsely low results.

Nursing Implications and Procedure


  • 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 in evaluating vitamin toxicity or deficiency.
  • 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 gastrointestinal, genitourinary, hepatobiliary, immune, and musculoskeletal systems; symptoms; and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • 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.
  • Instruct the patient to fast for at least 12 hr before specimen collection for vitamin A.
  • Note that there are no fluid or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Ensure that the patient has complied with dietary restrictions; assure that food has been restricted for at least 12 hr prior to the vitamin A test.
  • 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 health-care provider (HCP), who will discuss the results with the patient.
  • Nutritional Considerations: Educate the patient with a specific vitamin deficiency, as appropriate, regarding dietary sources of these vitamins. Advise the patient to ask a nutritionist to develop a diet plan recommended for his or her specific needs.
  • Vitamin A
  • Nutritional Considerations: Educate the patient with vitamin A deficiency, as appropriate, that the main dietary source of vitamin A is carotene, a yellow pigment noticeable in most fruits and vegetables, especially carrots, sweet potatoes, squash, apricots, and cantaloupe. It is also present in spinach, collards, broccoli, and cabbage. This vitamin is fairly stable at most cooking temperatures, but it is destroyed easily by light and oxidation.
  • Vitamin B1
  • Nutritional Considerations: Vitamin B1 is the most stable with respect to the effects of environmental factors. Educate the patient with vitamin B1 deficiency, as appropriate, that the main dietary sources of vitamin B1are meats, coffee, peanuts, and legumes. The body is also capable of making some vitamin B1 by converting the amino acid tryptophan to niacin.
  • Vitamin B6
  • Nutritional Considerations: Educate the patient with vitamin B 6 deficiency, as appropriate, that the main dietary sources of vitamin B6 include meats (especially beef and pork), whole grains, wheat germ, legumes (beans, peas, lentils), potatoes, oatmeal, and bananas. As with other water-soluble vitamins, it is best preserved by rapid cooking, although it is relatively stable at most cooking temperatures (except frying) and when exposed to acidic foods. This vitamin is destroyed rapidly by light and alkalis.
  • Vitamin C
  • Nutritional Considerations: Educate the patient with vitamin C deficiency, as appropriate, that citrus fruits are excellent dietary sources of vitamin C. Other good sources are green and red peppers, tomatoes, white potatoes, cabbage, broccoli, chard, kale, turnip greens, asparagus, berries, melons, pineapple, and guava. Vitamin C is destroyed by exposure to air, light, heat, or alkalis. Boiling water before cooking eliminates dissolved oxygen that destroys vitamin C in the process of boiling. Vegetables should be crisp and cooked as quickly as possible.
  • General
  • 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 (
  • 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.

Related Monographs

  • Related tests include amylase, BUN, chloride sweat, CBC, creatinine, lipase, prealbumin, TSH, FT4, and zinc.
  • Refer to the Gastrointestinal, Genitourinary, Hepatobiliary, Immune, 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
References in periodicals archive ?
Pyridoxyl-5-phosphate, or P-5-P, is a co-enzyme form of vitamin B6.
The coenzyme form of B6 is called Pyridoxyl-5-phosphate (P-5-P).