Vitamin B₇

Serum or plasma

1 mL

0.5 mL (Note: This volume does not allow for repeat testing.)

Red-top tube or lavender-top (EDTA) tube

Measurement of vitamin B₇ level

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

0.05−0.83 ng/mL

Biotin is a colorless, water-soluble B-complex vitamin that is also referred to as vitamin B₇.^1-3 Biotin functions as a cofactor for five mammalian enzymes that catalyze specific carboxylation reactions.² These are:

• Acetyl-CoA carboxylase I and II: catalyze the carboxylation of acetyl CoA to form malonyl CoA which, in turn, serves as a substrate for fatty acid elongation. These enzymes function in cytosolic fatty acid synthesis and in regulating mitochondrial fatty acid oxidation.

• Pyruvate carboxylase: catalyzes the carboxylation of pyruvate to form oxaloacetate, which serves as an intermediate in the citric acid cycle. This reaction is involved in gluconeogenesis, the production of glucose from other carbohydrates by the liver, kidney, and other gluconeogenic tissues.

• Methylcrotonyl-CoA carboxylase: catalyzes an essential step in the catabolism of leucine, an essential, branch-chained amino acid.

• Propionyl-CoA carboxylase: catalyzes essential steps in the metabolism of several amino acids, cholesterol, and odd chain fatty acids.¹

Biotin is also covalently attached to histone proteins that are essential for the folding of DNA into chromatin. It has been suggested that the biotinylation of histones might play a role in cell proliferation, gene silencing, and cellular response to DNA damage.⁴

Clinically advanced biotin deficiency is rare in the general population; however, significant biotin deficiency can occur in individuals who consume raw egg white over long periods.^1,2 Avidin, an antimicrobial protein found in egg white, binds biotin and prevents its absorption. Cooking egg white denatures avidin and wipes out its biotin-binding capacity.¹ Profound biotin deficiency can also occur in cases of drastically diminished biotin absorption (patients taking total parenteral nutrition without biotin and in some malabsorption conditions).^1,2 Some forms of liver disease may increase the requirement for biotin and result in clinical deficiency.^1,5 Patients receiving long-term anticonvulsant medication may also be at increased the risk for biotin deficiency.^1,2 The results of several studies suggest that biotin deficiency may also be relatively common during pregnancy.^1,6

Physical findings associated with overt biotin deficiency include a red scaly rash around the eyes, nose, mouth, and genital area.^1-3,7 Some reports suggest that biotin deficiency may result in brittle finger nails and that high dose supplementation may, to some extent, ameliorate the condition.^1,2,7 Adults with this deficiency experience thinning of hair, frequently with loss of hair color. Reported neurologic symptoms have included depression, lethargy, hallucination, and paresthesia of the extremities. Individuals with hereditary disorders of biotin metabolism also suffer from impaired immune system function and susceptibility to bacterial and fungal infections.^1-3,8