Tyrosine - Quantitative, EDTA Plasma

Blood

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Fasting Required

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Amino acid quantification.

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Tyrosine - Quantitative EDTA Plasma Test Guide

Why is it done?
- Measures circulating plasma levels of tyrosine, a non-essential amino acid that serves as a precursor for important neurotransmitters (dopamine, norepinephrine, epinephrine) and thyroid hormones
- Screens for tyrosinemia and other amino acid metabolism disorders, particularly in newborn screening programs and metabolic disease evaluation
- Evaluates hepatic synthetic function and protein metabolism status in patients with liver disease or nutritional compromise
- Detects inborn errors of metabolism affecting amino acid catabolism and transport
- Typically performed during newborn screening, in metabolic workup of developmental delay or neurological symptoms, and in monitoring of known tyrosinemia or hepatic dysfunction
Normal Range
- Reference Range: 45-150 μmol/L (micromoles per liter) in adults; values may vary slightly by laboratory
- Newborn Values: 20-100 μmol/L (typically lower than adults due to immature hepatic metabolism)
- Units of Measurement: μmol/L (micromoles per liter) or mg/dL; conversion factor 1 mg/dL = 55.2 μmol/L
- Interpretation: Normal values indicate appropriate amino acid metabolism and hepatic function. Values below reference range may indicate nutritional deficiency or certain genetic conditions. Values above reference range suggest metabolic disorders, liver disease, or tyrosinemia. Borderline elevations require clinical correlation and repeat testing.
Interpretation
- Elevated Tyrosine (>150 μmol/L): May indicate tyrosinemia types I, II, or III; hepatic cirrhosis or acute hepatitis; renal failure; protein malnutrition followed by refeeding; medications affecting amino acid metabolism; or severe infections. Requires investigation based on clinical presentation and additional amino acid profiles.
- Low Tyrosine (<45 μmol/L): May suggest phenylketonuria (PKU) if phenylalanine is elevated; severe malnutrition or protein deficiency; certain amino acid transport disorders; or advanced liver disease with loss of synthetic function.
- Markedly Elevated (>500 μmol/L): Highly suggestive of tyrosinemia type I (hepatorenal tyrosinemia); requires immediate follow-up with organic acid analysis, succinylacetone testing, and geneticist referral.
- Factors Affecting Results: Sample collection timing (circadian rhythm variations), hemolysis, improper anticoagulant use, protein intake patterns, age (newborns typically lower), liver function, renal function, medications (particularly immunosuppressants and some antibiotics), and specimen storage conditions.
- Clinical Significance: This test is clinically significant for early detection of inborn errors of metabolism, assessment of hepatic synthetic capacity, and monitoring of nutritional status. In newborns, elevated tyrosine is an important red flag for potentially life-threatening metabolic disorders requiring rapid intervention.
Associated Organs
- Primary Organs: Liver (primary site of tyrosine catabolism and metabolism); kidneys (involved in amino acid filtration and reabsorption); brain (tyrosine precursor for neurotransmitters); and thyroid gland (tyrosine substrate for thyroid hormone synthesis).
- Associated Conditions - Tyrosinemia: Type I (hepatorenal tyrosinemia) - most severe; presents with liver failure, renal tubular dysfunction, neurological crises, and increased hepatocellular carcinoma risk. Type II (oculocutaneous tyrosinemia) - characterized by eye inflammation, photophobia, and skin erosions. Type III (mild/asymptomatic tyrosinemia) - usually benign with minimal symptoms.
- Associated Conditions - Other Disorders: Chronic liver disease (cirrhosis, hepatitis); acute liver failure; renal insufficiency; phenylketonuria (PKU) with secondary tyrosine elevation; severe infections and sepsis; malnutrition and kwashiorkor; certain medications inducing hepatotoxicity.
- Potential Complications: Untreated tyrosinemia type I can lead to progressive hepatic failure, end-stage renal disease, neurological crises with sudden paralysis, hepatocellular carcinoma development, and death if not managed. Early detection and treatment with nitisinone can prevent or slow disease progression significantly.
Follow-up Tests
- If Elevated Tyrosine: Comprehensive amino acid panel (plasma and urine); succinylacetone quantitation (highly specific for tyrosinemia type I); organic acid analysis; phenylalanine level (to differentiate from PKU); liver function tests (AST, ALT, bilirubin, alkaline phosphatase, INR); renal function panel (creatinine, BUN); urinalysis; and hepatic ultrasound or imaging.
- If Tyrosinemia Type I Confirmed: Genetic testing for FAH gene mutations; hepatology and metabolic genetics consultation; AFP (alpha-fetoprotein) monitoring for hepatocellular carcinoma screening; regular abdominal ultrasound and CT scan; ophthalmologic examination; and baseline neurological assessment.
- If Monitoring Known Condition: Repeat plasma tyrosine quantitation every 3-6 months; ongoing liver function monitoring every 1-3 months; regular renal function assessment; dietary evaluation with metabolic nutritionist; medication compliance monitoring; and consideration of repeat testing during acute illness.
- Complementary Tests: Methionine level (often elevated in tyrosinemia); plasma amino acid ratio analysis; urine amino acids and organic acids; prothrombin time (PT); ammonia level; albumin and prealbumin; and in newborns, repeat screening at 7-14 days of life.
Fasting Required?
- Fasting Requirement: No - Fasting is NOT required for plasma tyrosine quantitation. The test can be performed at any time of day.
- Sample Collection Timing: For optimal consistency, morning collection (8-10 AM) is preferred as amino acid levels show circadian variation; however, non-fasting samples are acceptable.
- Medication Considerations: Continue all routine medications unless specifically instructed otherwise by physician; inform the laboratory of any immunosuppressants, antibiotics (especially aminoglycosides), corticosteroids, or amino acid supplements being taken as these may affect results.
- Patient Preparation: Avoid strenuous exercise for 24 hours before collection (may alter amino acid levels); maintain normal diet and protein intake; remain hydrated; arrive well-rested if possible; inform phlebotomist of any recent infections, illness, or dietary changes; for newborn screening, collect after 24 hours of life but preferably by day 5-7.
- Specimen Requirements: EDTA (lavender-top) plasma tube is required; specimen must be properly labeled with patient name, date, and time of collection; keep specimen cool and transport to laboratory promptly (within 2-4 hours); some laboratories require immediate freezing at -20°C if delay anticipated.

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