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Test Code BIOTS Biotinidase, Serum

Reporting Name

Biotinidase, S

Useful For

Preferred test for the diagnosis of biotinidase deficiency

 

Follow-up testing for certain organic acidurias

Method Name

Colorimetric

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum


Ordering Guidance


Molecular testing is available, see BTDZ / Biotinidase Deficiency, BTD Full Gene Analysis, Varies.

 

If measurement of biotin concentration is requested, order BIOTN / Biotin, Serum.



Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Centrifuge immediately and aliquot serum into plastic vial.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen (preferred) 21 days
  Refrigerated  5 days

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus OK

Reference Values

3.5-13.8 U/L

Day(s) Performed

Monday, Thursday

CPT Code Information

82261

LOINC Code Information

Test ID Test Order Name Order LOINC Value
BIOTS Biotinidase, S 1982-8

 

Result ID Test Result Name Result LOINC Value
50672 Biotinidase, S 1982-8
50673 Interpretation 59462-2
50675 Reviewed By 18771-6

Clinical Information

Biotinidase deficiency is an autosomal recessive disorder caused by variants in the biotinidase gene (BTD). Age of onset and clinical phenotype vary among individuals depending on the amount of residual biotinidase activity. Profound biotinidase deficiency occurs in approximately 1 in 137,000 live births and partial biotinidase deficiency occurs in approximately 1 in 110,000 live births, resulting in a combined incidence of about 1 in 61,000. The carrier frequency for biotinidase deficiency within the general population is about 1 in 120.

 

Untreated profound biotinidase deficiency typically manifests within the first decade of life as seizures, ataxia, developmental delay, hypotonia, sensorineural hearing loss, vision problems, skin rash, and alopecia. Partial biotinidase deficiency is associated with a milder clinical presentation and may include cutaneous symptoms without neurologic involvement. Certain organic acidurias, such as holocarboxylase synthase deficiency, isolated carboxylase synthase deficiency, and 3-methylcrotonylglycinuria, present similarly to biotinidase deficiency. Serum biotinidase levels can help rule out these disorders.

 

Treatment with biotin is successful in preventing the clinical features associated with biotinidase deficiency. In symptomatic patients, treatment will reverse many of the clinical features except developmental delay, vision, and hearing complications. As a result, biotinidase deficiency is included in most newborn screening programs. This enables early identification and treatment of presymptomatic patients.

 

Molecular tests are useful for confirmation of diagnosis or carrier testing. When biotinidase enzyme activity is deficient, sequencing of the entire BTD gene (BTDZ / Biotinidase Deficiency, BTD Full Gene Analysis, Varies) allows for detection of disease-causing variants in affected patients. Identification of familial variants allows for testing of at-risk family members (FMTT / Familial Variant, Targeted Testing, Varies).

 

While genotype-phenotype correlations are not well established, it appears that certain genetic variants are associated with profound biotinidase deficiency, while others are associated with partial deficiency.

Interpretation

An interpretive report is provided.

 

Values below 3.5 U/L are occasionally seen in specimens from unaffected patients.

Cautions

A diet high in biotin may result in normal clinical presentation even when the biotinidase level is low.

 

Assay interference may occur for specimens collected when the patient is being treated with a sulfa drug.

Method Description

Biotinidase activity is determined colorimetrically by measuring p-aminobenzoate liberation from N-biotinyl-p-aminobenzoate at 546 nm. Activity is determined from a standard curve of p-aminobenzoic acid. Modified Sigma substrate is used.(Wolf B, Grier RE, Allen RJ, et al. Biotinidase deficiency: the enzymatic defect in late-onset carboxylase deficiency. Clin Chim Acta. 1983;131(3):273-281; Cowan T, Pasquali M. Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw-Hill; 2017:1139-1158)

Report Available

2 to 5 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

Genetics Test Information

Preferred test to rule out biotinidase deficiency.