Guanidinoacetate and creatine, urine

Clinical background:

For investigation of suspected metabolic disorders of creatine biosynthesis or transport.  These disorders cause intellectual disability, speech impairment and epilepsy due to cerebral creatine deficiency.

Specimen container paediatric:

Urine

Specimen container adult:

Urine

Minimum volume paediatric:

1 mL 

Minimum volume adult:

1 mL 

Special requirements:

Freeze as soon as possible, within 2 hours if possible.

Transport requirements:

NuTH Trust users: send sample to the laboratory to arrive within 2 hours. External users: freeze the urine sample within 2 hours of collection and keep frozen during transport.

Reference ranges:

Creatine

< 5 years 6 – 1303 µmol/mmol creatinine

5 – 12 years 9 – 617 µmol/mmol creatinine

> 12 years 5 – 58 µmol/mmol creatinine Guanidinoacetate

< 4 years 19 – 210 µmol/mmol creatinine

4 – 12 years 10 – 125 µmol/mmol creatinine

> 12 years 10 – 69 µmol/mmol creatinineFactors affecting result:

Creatine is produced by metabolism of creatinine in urine at ambient temperature which may result in falsely elevated results if samples are not frozen promptly.