Person—creatinine serum level, total micromoles per litre NN[NN]

Guide for use:

There is no agreed standard as to which units serum creatinine should be recorded in.

Note: If the measurement is obtained in mmol/L it is to be multiplied by 1000.

Origin:
Caring for Australians with Renal Impairment (CARI) Guidelines. Australian Kidney Foundation

Comments:

Serum creatinine can be used to help determine renal function. Serum creatinine by itself is an insensitive measure of renal function because it does not increase until more than 50% of renal function has been lost.

Serum creatinine together with a patient's age, weight and sex can be used to calculate glomerular filtration rate (GFR), which is an indicator of renal status/ function. The calculation uses the Cockcroft-Gault formula.

Creatinine is normally produced in fairly constant amounts in the muscles, as a result the breakdown of phosphocreatine. It passes into the blood and is excreted in the urine. Serum creatinine can be used to help determine renal function. The elevation in the creatinine level in the blood indicates disturbance in kidney function.

GFR decreases with age, but serum creatinine remains relatively stable. When serum creatinine is measured, renal function in the elderly tends to be overestimated, and GFR should be used to assess renal function, according to the Cockcroft-Gault formula:

GFR (ml/min) = (140 - age [yrs]) x body wt (kg) [x 0.85 (for women)]
814 x serum creatinine (mmol/l)

An alternative formula is derived from the Modification of Diet in Renal Disease (MDRD) study and does not rely on knowledge of body weight:

GFR (ml/min/1.73m2) = 32788 x creatinine^-1.154 (umol/L) x age^-0.203 x (males: 1, females: 0.742).

To determine the degree of chronic renal impairment

GFR > 90ml/min - normal

GFR >60 - 90ml/min - mild renal impairment

GFR >30 - 60ml/min - moderate renal impairment

GFR 0 - 30 ml/min - severe renal impairment

Note: The above GFR measurement should be for a period greater than 3 months. GFR may also be assessed by 24-hour creatinine clearance adjusted for body surface area.

In general, patients with GFR < 30 ml/min are at high risk of progressive deterioration in renal function and should be referred to a nephrology service for specialist management of renal failure.

Patients should be assessed for the complications of chronic renal impairment including anaemia, hyperparathyroidism and be referred for specialist management if required.

Patients with rapidly declining renal function or clinical features to suggest that residual renal function may decline rapidly (ie. hypertensive, proteinuric (>1g/24hours), significant comorbid illness) should be considered for referral to a nephrologist well before function declines to less than 30ml/min. (Draft CARI Guidelines 2002. Australian Kidney Foundation). Patients in whom the cause of renal impairment is uncertain should be referred to a nephrologist for assessment.