Amino Acids Quantitation, Plasma / Urine / CSF

Specimen requirement

 

 Plasma Urine (Spot Urine) CSF

Paediatric heparin tube

 

Number of vials: 2

 

Minimum blood volume: 2.6 mL

Plain bottle

 

Volume: 5 mL

 

Minimum volume: 1 mL

Plain CSF bottle

 

Volume: 1 mL

 

Minimum volume: 0.2 mL

Paired plasma sample is required.

 

Authorisation code required

 No No No

24 Hr available service

 No No No

Precaution

Collect one full tube of blood, cap and mix thoroughly.

 

Avoid bacterial and fecal contamination to the urine sample.

 

Relevant information (including patient’s information, clinical presentation, biochemical abnormalities, diet, and treatment) must be provided either by an information sheet for metabolic screening, or data entered into the GCRS system.

Method

High performance liquid chromatography (HPLC)

Reference interval

 Sources:

Plasma reference range:

Modified from E. Shapira et al, 1989. Biochemical Genetics: a laboratory manual

Urine reference range:

Modified from R. Venta, 2001. Clin Chem 47(3): 575 - 583

CSF reference range:

Modified from C.M. Jones et al, 2006. Annals of Clin. Biochem 43: 63 - 66

Clinical indication

Diagnosis of aminoacidurias due to overproduction of amino acid(s), e.g. phenylketonuria, rather than to failure of the kidney to reabsorb amino acid(s)

 

Monitoring treatment of these aminoacidurias when appropriate, e.g. phenylketonuria, homocystinuria

 

Common indications for amino acid testing include clinical situations such as:

  1. acute life-threatening episode;

  2. failure to thrive;

  3. recurrent vomiting;

  4. neurological deterioration;

  5. hyperammonemia;

  6. lethargy;

  7. metabolic acidosis; and

  8. testing or following therapy for a specific inborn error of metabolism (PKU, MSUD, tyrosinemia)

Listing of clinical information is particularly important for appropriate interpretation.

Result interpretation

Genetic diseases cause an increase in usually one amino acid (e.g. phenylalanine in phenylketonuria) or occasionally in a few metabolically related amino acids (e.g. homocystine and methionine in homocystinuria).       

 

Many non-specific abnormalities occur with non-genetic metabolic diseases.       

 

The most likely cause of increased plasma amino acids is a non-fasting specimen. When monitoring dietary management of the genetic diseases, the presence of low levels is also of significance (e.g. low tyrosine and phenylalanine in phenylketonuria).

Measurement of uncertainty

 See table.

Frequency of measurement

 Weekly