Biotinidase (EDTA whole blood)

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Enzyme test for biotin recycling.

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Biotinidase (EDTA whole blood) - Comprehensive Test Information Guide

Why is it done?
- Measures the enzyme biotinidase activity in whole blood to screen for biotinidase deficiency, a rare autosomal recessive metabolic disorder
- Part of newborn screening programs to detect biotinidase deficiency early and prevent serious neurological complications
- Identifies children who cannot effectively recycle and reuse biotin (vitamin B7), an essential cofactor for multiple carboxylase enzymes
- Typically performed during routine newborn screening within 24-48 hours after birth
- May be ordered in children with symptoms suggestive of biotinidase deficiency (alopecia, dermatitis, developmental delay, seizures, hearing loss)
- Can be used for genetic counseling in families with history of biotinidase deficiency
Normal Range
- Normal/Reference Values: >10 nmol/min/mL (or >3 U/mL depending on laboratory methodology) Most laboratories report values >8-10 nmol/min/mL as normal
- Partial Biotinidase Deficiency: Approximately 20-40% of normal activity Borderline values typically ranging from 3-10 nmol/min/mL
- Profound Biotinidase Deficiency: <3 nmol/min/mL (or <10% of mean normal activity) Indicates absent or severely reduced enzyme activity
- Units of Measurement: nmol/min/mL (nanomoles per minute per milliliter) U/mL (International Units per milliliter) in some laboratories Reference ranges may vary by laboratory and testing methodology
- Interpretation: Normal: Adequate biotinidase activity to recycle biotin and prevent deficiency Abnormal/Low: Insufficient enzyme activity, requires follow-up testing and possible biotin supplementation Borderline: Partial deficiency that may warrant repeat testing or consultation with metabolic specialist
Interpretation
- Normal Result (>10 nmol/min/mL): Indicates sufficient biotinidase enzyme activity Biotin recycling is functioning normally No risk of biotinidase deficiency Clinical manifestations of biotin deficiency are unlikely to develop
- Partial Biotinidase Deficiency (3-10 nmol/min/mL): Indicates reduced but present biotinidase activity Approximately 20-40% of normal enzyme function Individual can recycle some biotin but may not be completely sufficient during periods of increased biotin loss Generally asymptomatic but may benefit from biotin supplementation and close monitoring Requires repeat testing to confirm diagnosis
- Profound Biotinidase Deficiency (<3 nmol/min/mL): Indicates severe deficiency in biotinidase enzyme activity <10% of mean normal activity Significant risk of developing clinical manifestations without treatment Requires immediate biotin supplementation (typically 5-20 mg/day) Early intervention can prevent neurological, dermatological, and auditory complications Requires ongoing management and monitoring
- Factors Affecting Results: Genetic mutations in the BTD gene (autosomal recessive inheritance) Age of patient (newborn screening vs. older children/adults) Sample collection and handling (EDTA tube required) Laboratory testing methodology (spectrophotometric or fluorometric assays) Biotin supplementation prior to testing (may artificially normalize results) Recent transfusions may affect results if donor blood has normal biotinidase activity
- Clinical Significance: Early detection through newborn screening prevents irreversible neurological damage With treatment, prognosis is excellent and most symptoms are preventable or reversible Without diagnosis and treatment, can lead to permanent hearing loss, developmental delay, and seizures Partial deficiency may remain asymptomatic but requires monitoring Genetic counseling recommended for families with affected individuals
Associated Organs
- Primary Organ Systems Involved: Central Nervous System (CNS): Primary target organ for biotin-dependent enzymes Peripheral Nervous System: Site of neurological complications Skin and Hair Follicles: Dermatological manifestations common in deficiency Auditory System: Hearing loss is frequent complication Immune System: May affect immune competence
- Associated Conditions and Diseases: Biotinidase Deficiency: Core metabolic disorder detected by this test Developmental Delay and Intellectual Disability: If untreated Seizure Disorders: Common manifestation of profound deficiency Sensorineural Hearing Loss: May be irreversible if not treated early Alopecia: Biotin-dependent hair loss Atopic Dermatitis and Skin Manifestations: Eczema-like rashes Metabolic Acidosis: Related to impaired multiple carboxylase enzyme function Immune Deficiency: Increased susceptibility to infections
- Potential Complications if Untreated: Permanent neurological damage and severe developmental delay Irreversible sensorineural hearing loss and deafness Uncontrolled seizures and status epilepticus Ataxia and progressive neuromotor dysfunction Conjunctivitis and visual disturbances (episodic) Autoimmune-like manifestations Organic acidemia and metabolic complications Death in severe untreated cases (rare with modern screening)
- Benefits of Early Diagnosis: Early biotin supplementation prevents clinical manifestations Reversibility of dermatological and systemic symptoms Prevention of hearing loss and neurological complications Normal development and learning when treated from newborn period Improved quality of life and normal educational outcomes
Follow-up Tests
- Confirmatory Testing: Repeat biotinidase test on dried blood spot after 1-2 weeks Serum biotinidase activity measurement using quantitative assay Post-biotin supplementation biotinidase test (to assess substrate availability) Genetic testing for BTD gene mutations (confirmation of diagnosis)
- Assessment of Complications: Audiology evaluation and hearing screening Neuropsychological testing for developmental delay Neuroimaging (MRI) if seizures or neurological symptoms present EEG if seizure activity suspected Ophthalmology examination Immune function testing if recurrent infections noted
- Metabolic Monitoring: Plasma amino acid analysis (elevated lysine in deficiency) Organic acid profile (urinary organic acids) Acylcarnitine profile (elevated C-12:1 and other acylcarnitines) Lactate and pyruvate measurements Ammonia level (if metabolic complications present)
- Ongoing Monitoring: Repeat biotinidase testing: Every 6-12 months during treatment Growth and development monitoring: Regular pediatric evaluations Skin examination: Assess for dermatological manifestations Hearing assessment: Annual audiometry to monitor for ototoxicity Metabolic panel: Periodic checks of liver function and electrolytes Biotin level testing: May be performed at specialized metabolic centers
- Related and Complementary Tests: Multiple carboxylase deficiency screening (detects multiple enzyme dysfunction) Other newborn screening markers (other metabolic disorders may coexist) General metabolic panel Liver function tests (for metabolic complications) Family members testing (siblings should be screened)
- Monitoring Frequency for Diagnosed Cases: Initial Phase: Biotinidase testing at diagnosis and 1-2 weeks after start of treatment First Year: Clinical evaluation and assessment every 1-3 months Ongoing: At minimum annually with specialized metabolic center Hearing evaluation: At baseline, then annually or as clinically indicated More frequent monitoring if clinical symptoms emerge or dosing adjustments needed
Fasting Required?
- Fasting Status: NO - Fasting is NOT required for biotinidase testing
- Collection Instructions: Test can be performed at any time of day, fasting or non-fasting No dietary preparation necessary Routine infant feeding or adult eating patterns do not affect results Timing of test in relation to meals is not critical
- Sample Collection Requirements: EDTA (ethylenediaminetetraacetic acid) whole blood sample required Purple-top or lavender EDTA tube must be used Proper tube selection is critical for valid results Typically 3-5 mL of blood collected by venipuncture For newborn screening: Blood is collected on dried blood spot cards (heel prick) Samples may also be submitted as dried blood spots on filter paper
- Special Instructions: Inform laboratory if patient is currently taking biotin supplements (may affect results) Samples should be stored and transported at room temperature Avoid hemolysis (vigorous shaking) during sample handling Process samples within 24 hours when possible For newborn screening, collect between 24-48 hours after birth Heel prick for dried blood spots should be deep enough to fill circles completely
- Medications to Avoid: No specific medications need to be avoided before testing Biotin supplementation (if patient is currently taking it): Inform the laboratory as it may affect enzyme activity levels Continue all other routine medications as prescribed Anticonvulsants: Do not discontinue unless directed by physician Other vitamins and supplements: Generally do not require discontinuation
- Patient Preparation: No special preparation required for routine biotinidase testing For newborns: Inform parents that heel prick collection is standard procedure Explain purpose of test and that sample collection is brief and minimally painful For older children/adults: Standard phlebotomy precautions apply Ensure patient comfort during blood draw No need to restrict activities before or after test

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