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Stability of creatinine and cystatin C in whole blood
E M Spithoven1, S J L Bakker, J E Kootstra-Ros
1Division of Nephrology, Department of Internal Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Insights
Creatinine and cystatin C, key kidney function markers, are stable in whole blood for up to 48 hours at room temperature. Delayed separation does not impact their variability or estimated glomerular filtration rate (eGFR).
Area of Science:
- Clinical Chemistry
- Biomarker Stability
- Renal Function Assessment
Background:
- Limited data exists on the impact of delayed whole blood separation on creatinine and cystatin C stability.
- Understanding this stability is crucial for accurate kidney function assessment, especially in remote or delayed sample processing scenarios.
Purpose of the Study:
- To evaluate the stability of creatinine and cystatin C in whole blood stored at room temperature for up to 72 hours.
- To determine the effect of delayed plasma separation on the measured concentrations of these kidney function markers.
- To assess the impact of delayed separation on estimated glomerular filtration rate (eGFR) calculations.
Main Methods:
- Plasma samples from 45 patients were analyzed for creatinine and cystatin C concentrations.
- Whole blood samples were separated at different time points (0, 24, 48, 72 hours) to simulate delayed processing.
- Analyte stability was assessed by measuring concentration differences and calculating total change limits; eGFR was calculated using CKD-EPI equations.
Main Results:
- Creatinine and cystatin C remained stable in whole blood for up to 48 hours at room temperature (total change limits 3.3% and 3.9%, respectively).
- Delayed separation up to 48 hours did not increase variability in measured concentrations for either analyte.
- eGFR calculations using creatinine or cystatin C showed minimal differences (<3 mL/min/1.73 m²) even with delayed separation up to 48 hours; the combined CKD-EPI equation showed minimal difference even at 72 hours.
Conclusions:
- Creatinine and cystatin C are stable in whole blood stored at room temperature for up to 48 hours prior to plasma separation.
- Delayed blood processing within this timeframe does not significantly affect analyte variability or influence eGFR results.
- These findings support the reliability of using creatinine and cystatin C for kidney function assessment even with sample transport delays.
Background:
As yet little is known about the effect of delayed separation of whole blood stored at room temperature on the stability of the kidney function markers creatinine and cystatin C.
Methods:
We used plasma samples of 45 patients with a wide range of creatinine and cystatin C concentration. Samples were sent by post as whole blood, and differences in creatinine and cystatin C concentrations when measured (by enzymatic assay and PETIA, respectively) in plasma separated shortly after blood withdrawal or in plasma obtained after delayed separation at 24, 48 and 72 h. Intra- and inter-assay variability was assessed and total change limit was calculated to assess analyte stability.
Results:
Total change limit was 3.3% for creatinine and 3.9% for cystatin C. In whole blood creatinine and cystatin C remained stable up to 48 h. Delayed separation of whole blood did not induce more variability in measured concentrations of both analytes. Glomerular filtration rate estimated with the CKD-EPI equations showed less than 3 mL/min/1.73 m² difference when using creatinine or cystatin C concentration measured in plasma separated up to 48 h after blood withdrawal compared to plasma separated shortly after blood withdrawal. The new CKD-EPI equation that uses creatinine as well as cystatin C to estimate GFR showed even at 72 h less than 3 mL/min/1.73 m² difference.
Conclusions:
Creatinine and cystatin C remain stable in whole blood stored at room temperature up to 48 h before separation, and changes in these analytes during this time period do not affect variability and eGFR.
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