What this test measures
The amino acid profile quantifies the levels of essential, non-essential and selected non-protein amino acids in plasma — usually around 35 analytes including phenylalanine, tyrosine, leucine, isoleucine, valine, methionine, homocystine, ornithine, citrulline, arginine, glycine, alanine, glutamine, glutamic acid, lysine and others. Each pattern of derangement points to a specific metabolic disorder.
Examples — high phenylalanine and low tyrosine suggest phenylketonuria (PKU); high citrulline suggests urea cycle disorders; high leucine, isoleucine and valine suggest maple syrup urine disease (MSUD); high methionine and homocystine suggest homocystinuria. The test is interpreted by a metabolic specialist alongside urine organic acids, acyl-carnitine profile and clinical features.
Why it matters
India has the largest birth cohort in the world and a significant burden of inborn errors of metabolism — often undiagnosed because of limited newborn screening coverage. The amino acid profile is the key biochemical test for confirming many treatable IEMs (PKU, MSUD, urea cycle defects, organic acidaemias, homocystinuria) — many of which cause irreversible neurological damage if diagnosis is delayed.
Indications include unexplained encephalopathy in any age (especially neonates and children), recurrent vomiting / lethargy / hypotonia, developmental delay, intellectual disability, unexplained metabolic acidosis, persistent hyperammonaemia, family history of IEM, and consanguineous parents. Early diagnosis can be life-saving and life-changing — many IEMs are treatable with diet modification, cofactor supplementation, and (in some cases) substrate-reduction therapy.
How to prepare
Fasting morning sample preferred (4–6 hours minimum for older children and adults; 2–3 hours for infants). Patient should be on usual diet — do not stop protein in the days before the test. The sample must be processed promptly, separated and frozen if not analysed quickly. Mention all medications, dietary supplements, recent illnesses, and any family history of metabolic disease. Confirm with the lab in advance.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Quantitative Amino Acid Panel (~35 analytes) (µmol/L)[1][2] | Each amino acid has a separate age-specific reference range — interpreted by a metabolic specialist | Pattern-based — generalised low amino acids suggest malnutrition or malabsorption; specific low amino acids can be diagnostic (low citrulline + arginine in ornithine transcarbamylase deficiency, low alanine in pyruvate disorders). | Pattern-based interpretation — high phenylalanine + low tyrosine = phenylketonuria (PKU); high leucine, isoleucine, valine, alloisoleucine = maple syrup urine disease (MSUD); high methionine + homocystine = homocystinuria; high citrulline = citrullinaemia; high glutamine + low BCAA = liver failure; high tyrosine = tyrosinaemia. Always interpreted alongside urine organic acids and acyl-carnitine profile. |
Pattern-based amino acid diagnosis
| Pattern | Suggested disorder | Treatment overview |
|---|---|---|
| High Phe, low Tyr | Phenylketonuria (PKU) | Low-phenylalanine diet for life; lifelong monitoring |
| High Leu, Ile, Val + alloisoleucine | Maple Syrup Urine Disease (MSUD) | Specialised low-BCAA diet; thiamine trial; transplant in severe forms |
| High Met + Homocystine | Homocystinuria (CBS deficiency) | Pyridoxine, folate, betaine, low-methionine diet |
| High Citrulline + hyperammonaemia | Citrullinaemia (type 1 or 2) | Low-protein diet, arginine/citrulline, ammonia scavengers |
| Low Citrulline + hyperammonaemia | OTC / CPS1 deficiency | Low-protein, ammonia scavengers, possible transplant |
| High Glutamine, low BCAA | Liver failure | Treat underlying liver disease |
| Generalised low amino acids | Severe malnutrition / malabsorption | Nutritional rehabilitation |
Frequently asked questions
When is the amino acid profile ordered?
In suspected inborn errors of metabolism — unexplained encephalopathy or coma in neonates / children, recurrent vomiting, hypotonia, developmental delay, intellectual disability, unexplained metabolic acidosis, persistent hyperammonaemia, family history of IEM, or consanguineous parents. Also in adults with unexplained metabolic or psychiatric symptoms suggesting a late-presenting IEM.
Do I need to fast?
Yes — fasting morning sample (4–6 hours in adults / older children; 2–3 hours in infants). Stay on usual diet — protein restriction before testing can obscure the diagnosis.
Is this the same as a newborn screen?
No — but related. Newborn screening (dried blood spot) screens for several disorders including PKU, MSUD, congenital hypothyroidism and others. A confirmatory plasma amino acid profile is run if the screen is abnormal or if clinical suspicion is high.
Why do I also need a urine organic acid test?
Amino acid and urine organic acid profiles are complementary. Organic acidaemias (methylmalonic, propionic, isovaleric) are best identified by urine organic acids; amino acidopathies by plasma amino acids; fatty acid oxidation defects by acyl-carnitine profile. A metabolic specialist usually orders the right combination.
How are inborn errors of metabolism treated?
Depends on the specific disorder — examples include low-phenylalanine diet for PKU, low-BCAA diet for MSUD, ammonia scavengers + arginine / citrulline for urea cycle disorders, biotin for biotinidase deficiency. Early diagnosis is essential; many disorders are treatable to good outcomes if caught early.
Is this test available widely in India?
It is offered in major tertiary hospitals, paediatric and adult metabolic centres, and select reference labs (Sandor, NIMHANS, AIIMS, Centre for Human Genetics, Mayo, MedGenome). Confirm availability with your specialist.
What is the role of genetic testing?
Once a metabolic disorder is suspected biochemically, targeted genetic testing confirms the diagnosis, allows family counselling, prenatal diagnosis for future pregnancies, and (for some disorders) guides specific therapy. Increasingly, exome / whole-genome sequencing is the next step.
Related Other / Biochemistry tests
Tests commonly ordered alongside AMINO ACID PROFILE (35), or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Inborn Errors of Metabolism · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Laboratories — Plasma Amino Acid Profile · accessed 2026-05-30T00:00:00.000Z
- Indian Academy of Pediatrics — Newborn Screening and IEM · accessed 2026-05-30T00:00:00.000Z
- Society for Inherited Metabolic Disorders — Practice Guidelines · accessed 2026-05-30T00:00:00.000Z
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