Pathology Handbook

Plasma Amino Acids

Clinical Indications

Plasma amino acids may be abnormal in a variety of amino acid disorders, urea cycle defects and some organic acidurias. If possible, investigations should be carried out on samples taken when the patient is symptomatic.

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Analysed by referral laboratory if specific criteria met

Patient Preparation

Plasma amino acids fluctuate widely depending on the protein intake and whether the patient is in a fed or fasted state. Dietary restrictions may cause characteristic amino acid patterns to disappear and result in false negative results. 

Collect sample during acute illness if possible, state feeding and advise if protein has been withdrawn.

In a non-acute situation, a fasting sample is preferred (2-3 hrs post feed in infants)

Turnaround Time

2 weeks


Heparin plasma


1.0 ml


Vacutainer green top


Samples should be transported to laboratory immediately

Lab Handling

Sent to referral laboratory (Addenbrookes, Cambridge)

Causes for Rejection

Unlabelled or incorrectly labelled sample; not meeting specific criteria for analysis; delay in sample reaching laboratory or in wrong sample container.  Haemolysed samples are unsuitable

Results and interpretation

See laboratory report