Blood Urea and Creatinine Stability Determined for Chemistry Analyzer

Serum creatinine values of patients tend to change as a result of the use of different blanks used for creatinine determinations on some clinical chemistry analyzers.

A general quality assurance program in clinical chemistry laboratories is an essential part of monitoring the stabilities of determinations on what are commonly known as stat analytes, including sodium, potassium, chloride, bicarbonate, calcium, glucose, blood urea nitrogen (BUN), and creatinine.

Medical laboratory scientists at the New York Harbor Veteran Affairs Medical Center (Brooklyn, NY, USA) investigated the reproducibility of creatinine values, by determining the serial creatinine values in the sera of 13 patients whose initial values were either in the reference range or elevated (range 0.58 to 7.8 mg/dL). They determined BUN and creatinine values, using the glutamate dehydrogenase linked enzyme assay system and the Jaffe method, respectively.

Determination of all values was performed on the Siemens Advia 1800 chemistry analyzer (Siemens Healthcare; Tarrytown, NY, USA) using the method for creatinine, which uses the formation of a complex of creatinine with picric acid, and for BUN values urease-catalyzed release of ammonia was measured by the glutamate dehydrogenase system. The creatinine values were determined concurrently with serum blood urea nitrogen (BUN) determinations, range 6.0 to 84.4 mg/dL, as these two analytes are used together in evaluation of renal function.

The scientists found that all values for creatinine on samples stored at 4 °C were reproducible as were the corresponding BUN values, which is revealed by low values for the coefficients of variation (CV). One sample with relatively high CV of 10.6% for creatinine was found to have an initial value of 1.1 mg/dL, in the reference range; but, on repeat determinations, the obtained levels were as high as 1.5 mg/dL, above the reference range. BUN values for this sample remained in the reference range, suggesting that no renal disease was present.

The authors concluded that the precision of the serum BUN assays on the Advia 1800 analyzer is quite high over the prolonged time period of 15 days. The same conclusion applies to serum creatinine assay results on this analyzer with the caveat that borderline values can show less precision-making evaluation of renal function more difficult. The study was published on November 11, 2013, in the Journal of Clinical Laboratory Analysis.

Related Links:
New York Harbor Veteran Affairs Medical Center
Siemens Healthcare