Specimen requirement

Plasma

Urine

Fluid

Adult patient:

  Heparin gel tube

Minimum blood volume: 5 mL

Spot urine:

Plain bottle

Minimum volume: 10 mL

24 Hr urine:

U1 bottle / U2 bottle

Spot fluid:

Plain bottle

Minimum volume: 10 mL

Paediatric patient:

Paediatric heparin tube

Number of vials: 1

Minimum blood volume: 1.3 mL

Authorisation code required

No

24 Hr available service

Yes

(Call extension: 3353 for express result)

Spot urine: Yes

24 Hr urine: No

No

Method

Spectrophotometry

Reference interval

Plasma:

(Source:
Reagent inserts: CREJ 2014 - 06, V9.0; CREP2 2016 - 02,V8.0

Schlebush H, Liappis N, Klein G.  Creatinine and ultrasensitive CRP: Reference Internals from Infancy to Childhood. J Lab Med 2002; 26: 341 - 346)

Reference intervals for children < 3 yr are quoted with enzymatic assay, and kinetic colourimetric assay for subjects > 3 yr.

 

Male:	65 – 109 µmol/L
Female:	49 – 83 µmol/L

(Source: from local population study in 2008)

Urine:

 

Male:	7.1 – 17.7 mmol/d
Female:	5.3 – 15.9 mmol/d

Creatinine clearance:

(Source: Textbook of Clinical Chemistry 3rd Edition, Norbert W Tietz, Saunders)

Estimated Glomerular Filtration Rate (EGFR): Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Formula

CKD-EPI (mL/min/1.73 m²)
= 141 x min( sCr / k, 1)^a x max( sCr / k, 1)^-1.209 x (0.993)^Age x 1.018 [if female]

Assumptions:

The patient is not of African black origin
sCr in µmol/L measured by IDMS traceable method, age in years
k = 61.9 for females or 79.6 for males
a = -0.329 for females or -0.411 for males
min = minimum value of sCr/k or 1
max = maximum value of sCr/k or 1

[Traceability / Source:
Plasma Cr is traceable to IDMS method. EGFR < 60 units (mL/min/1.73 m²) has more clinical implications for classification of kidney dysfunctions.
(Ann Intern Med. 2009; 150 (9): 604 - 612. NIDDK website www.niddk.nih.gov)].

Clinical indication

Plasma creatinine:

 
To assess kidney function.

Urine creatinine:

To calculate creatinine clearance, to calculate an analyte / creatinine ratio and to assess the completeness of a 24 Hr collection.

Fluid creatinine:

To assess whether there may be urine contamination.

Result interpretation

Increased creatinine levels occur in conditions which decrease the glomerular filtration rate. These may be pre-renal (e.g. hypovolaemia, hypotension), renal or post-renal (e.g. obstruction).

An artefactual increase in creatinine is seen with some methods in the presence of ketones and some cephalosporins - consult pathologist.

Cyanokit (Hydroxocobalamin) may cause interference with results.

Levels are lower in patients with a reduced muscle mass (e.g. the elderly) and this may conceal impairment of renal function.

Creatinine clearance is more sensitive than serum creatinine for the detection of early glomerular dysfunction, but significant decreases in creatinine clearance may not occur until up to 30% of glomeruli cease to function.

MDRD is an estimate of GFR. It has not been fully validated in Chinese, children, elderly > 75 yrs, pregnant women, patients with serious co-morbidity or extreme body size / muscle-mass / nutritional status.

Measurement of uncertainty

See table.

Frequency of measurement

Daily