| Serum Creatinine Standardisation |
|
In response to a world wide trend to standardise plasma creatinine measurements (in line with Isotope Dilution Mass spectrometry IDMS) the Biochemistry Department will introduce a protein correction factor in the serum creatinine assay.
The change will take effect on June 2nd 2009.
Current assay: Uncompensated Jaffe
Standardized assay: IDMS traceable Jaffe
The new standardised method will deliver slightly different results for patients, particularly at low creatinine concentrations and as a result, reference ranges will need to be altered as per the table below.
|
|
IDMS traceable Jaffe Creatinine
(standardised method) |
Uncompensated Jaffe Creatinine
(existing method) |
|
Serum / Plasma |
µmol/L |
µmol/L |
|
Male |
64 – 104 |
50 - 110 |
|
Female |
49 – 90 |
50 - 90 |
|
|
|
|
|
Neonate |
40 - 100 |
40 - 100 |
|
Infant |
40 - 60 |
40 - 60 |
|
Child |
40 - 100 |
40 - 100 |
|
|
|
|
|
Urine |
µmol/kg/d |
µmol/kg/d |
|
Male |
124 – 230 |
124 – 230 |
|
Female |
98 - 177 |
98 - 177 |
The calculation of the eGFR will also change:
eGFR (mL/min/1.73 m2) = 175 x (SCr/88.4)-1.154 x (Age)-0.203 x (0.742 if female)
(x 1.210 if African American)
Urine Creatinine and reference interval will not be affected.
Examples:
Patient: Mr. A (Age 56, European)
Creatinine results (decision level):
108 µmol/L (IDMS method)
126 µmol/L (existing uncompensated Jaffe)
eGFR
62 mL/min/1.73 m2 (IDMS method)
55 mL/min/1.73 m2 (existing method)
Patient Mr. B (Age 46, European)
Creatinine result (elevated)
439 µmol/L (IDMS method)
449 µmol/L (existing uncompensated Jaffe)
eGFR
13 mL/min/1.73 m2 (IDMS method)
13 mL/min/1.73 m2 (existing method)
- The National Kidney Disease Education Program (NKDEP) recommends reporting eGFR values above 60 mL/min/1.73 m2 simply as ">60 mL/min/1.73 m2," not as an exact number. Because measurement bias and imprecision have a larger impact on eGFR variability as serum creatinine values get lower (GFR gets higher)
- For values 60 mL/min/1.73 m2 and below, the report should give the numerical estimate rounded to a whole number (e.g., "32 mL/min/1.73 m2").Because, at eGFR <60 mL/min/1.73 m2 (higher serum creatinine) the bias and imprecision have less impact on the variability and thus less impact on the clinical reliability of eGFR.
Any queries should be directed to Dr Malcolm Mohr (Chemical Pathologist) at Malcolm.Mohr@mh.org.au | 
