Creatinine, Plasma

Diagnostic Use

Creatinine is a waste product produced by skeletal muscle tissue. Creatinine is produced at a constant rate (dependent upon muscle mass) and is freely filtered at the glomerulus (with a small fraction of creatinine being excreted in the distal nephron). Because of these properties, creatinine is a useful biomarker of glomerular filtration.

Creatinine is the most commonly requested biomarker of renal function.

Department

Core Biochemistry

Delphic Registration Code

CRN

Synonyms

CRN, plasma

Turnaround Time

3 hours

Test Code

5422

Specimen Type

• Serum
• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Preferred if West Coast

• Lithium Heparin - Gel (Light Green Cap)

Acceptable

• Serum (Red Cap)
• SST II (Gold Cap)
• Lithium Heparin - Gel (Light Green Cap)

Preferred Sample Volume (ml)

4.5

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Acceptable

• Lithium Heparin - Gel (Light Green Cap)

Preferred Sample Volume (ml)

0.6

Additional Specimen Information

Paediatric Specimen - Heparin microtainer tube 600 µL

Aliquot Instructions

Sample Type

• Serum
• Plasma

Minimum Volume (ml)

0.1

Interpretation

Creatinine is used to calculate the estimated glomerular filtration rate (eGFR), which gives an indication of overall glomerular function.  There is an inverse relationship between plasma creatinine concentration and eGFR.

Whilst creatinine reference intervals are quite wide, an individual’s creatinine result is expected to be relatively consistent over time.  As such, creatinine results are best interpreted in comparison with prior results for the same patient.  A result which is within the reference interval may be markedly abnormal for that particular patient if it represents an increase from prior results.

Creatinine concentration is also a function of muscle mass.  Therefore creatinine results are not a good estimate of GFR in patients at extremes of muscle mass (i.e. very low or very high muscle bulk).  Creatinine will underestimate GFR in amputees for similar reasons.  Cystatin C is an alternative renal biomarker which may provide a better estimate of GFR in these patients.

Creatinine will be overestimated in individuals using creatine supplements, as the assay cross-reacts with creatine.

Creatinine is not an early marker of renal impairment and may be normal in the early stages of acute kidney injury.

Reference Intervals

Age	Lower ref limit (μmol/L)	Upper ref limit (μmol/L)
< 1 month	20	60
1 month – 2 years	20	50
2-4 years	20	60
4-6 years	25	65
6-10 years	25	70
10-15 years	40	80
>15 years (M)	50	110
>15 years (F)	45	90

 

Test Method

Enzymatic spectrophotometry on a Beckman Coulter AU5822 analyser using Beckman Coulter reagents.

Non-Funded Test Cost

$3.24 (Exclusive of GST)

Billing Code

5422

Contact Information

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