Certification of creatinine in a human serum reference material by GC-MS and LC-MS.
BACKGROUND
To meet recommendations given by the Laboratory Working Group of the National Kidney Disease Education Program for improving serum creatinine measurements, NIST developed standard reference material (SRM) 967 Creatinine in Frozen Human Serum. SRM 967 is intended for use by laboratories and in vitro diagnostic equipment manufacturers for the calibration and evaluation of routine clinical methods.


METHODS
The SRM was produced from 2 serum pools with different creatinine concentrations. The concentrations were certified using a higher-order isotope-dilution GC-MS method and an isotope-dilution LC-MS method. The LC-MS method is a potential higher-order reference measurement procedure.


RESULTS
The GC-MS mean (CV) concentrations were 67.0 (0.9%) mumol/L for serum pool 1 and 346.1 (0.45%) mumol/L for serum pool 2. The LC-MS results were 66.1 (0.2%) mumol/L and 346.3 (0.2%) mumol/L, respectively. For serum pool 1, there was a 1.4% difference between the mean GC-MS and LC-MS measurements, and a 0.10% difference for serum pool 2. The results from the 2 methods were combined to give the certified concentrations and expanded uncertainties.


CONCLUSIONS
The certified concentration (expanded uncertainty) of SRM 967 was 66.5 (1.8) mumol/L for serum pool 1 (a value close to the diagnostically important concentration of 88.4 mumol/L) and 346.2 (7.4) mumol/L for serum pool 2 (a concentration corresponding to that expected in a patient with chronic kidney disease).
Analytical Chemistry Division and Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, USA. nathan.dodder@nist.gov
Nathan G
NG
Dodder
Susan S-C
SS
Tai
Lorna T
LT
Sniegoski
Nien F
NF
Zhang
Michael J
MJ
Welch
D001800:Blood Specimen Collection; D002138:Calibration; D002853:Chromatography, Liquid; D002908:Chronic Disease; D003404:Creatinine / Q000097:blood / Q000592:standards*; D005260:Female; D005615:Freezing; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007201:Indicator Dilution Techniques; D013058:Mass Spectrometry; D008875:Middle Aged; D011786:Quality Control; D012015:Reference Standards; D051437:Renal Insufficiency / Q000175:diagnosis; D044967:Serum
D003404:Creatinine