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PTD - 164

Test Directory -  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.

Request Form 

Combined Pathology Blood form (Yellow/Black or Blue for GP's) and Metabolic screening questionnaire


Referred test: Analysed by Biochemical Genetics Department, Addenbrookes Hospital if specific criteria met.

Specific Criteria

Requests should be accompanied by a completed Metabolic screening questionnaire which has been authorised by a Consultant.

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Collect sample during acute illness if possible, state feeding and advise if protein has been withdrawn.

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

Turnaround Time

3 weeks




1.0 ml


Paediatric orange top (lithium-heparin)

Samples should be transported to laboratory immediately.

Causes for Rejection

Unlabelled sample. Not meeting specific criteria for analysis. 
Delay in sample reaching laboratory. Haemolysed samples are generally unsuitable.

Reference range

Result reported as an interpretive comment.


Provided by the referral laboratory

Lab. Handling

Processing: Centrifuge and aliquot within 2 hours of collection into 2 tubes and freeze at -20C in separating freezer (CB40), active frozen rack 110.
PAA and send or BPRO and save in separating freezer (CB40) at -20C, saved frozen rack.

Version 1.2 / September 2015                                                                                                 Approved by: Consultant Biochemist