Point-of-care creatinine vs. central laboratory creatinine in the critically ill

Objective: Frequent measurement of creatinine by point-of-care testing (POCT) may facilitate the earlier detection of acute kidney injury (AKI) in critically ill patients. However, no robust data exist to confirm its equivalence to central laboratory testing. We aimed to conduct a multicenter study to compare POCT with central laboratory creatinine (CrC) measurement.

Design: Retrospective observational study, using hospital electronic medical records. Obtained paired point-of-care creatinine (CrP) from arterial blood gas machines and CrC.

Setting: Four intensive care units in Queensland, Australia.

Participants: Critically ill patients, where greater than 50% of POCT contained creatinine.

Main outcome measures: Mean difference, bias, and limits of agreement between two methods, and biochemical confounders.

Results: We studied 79,767 paired measurements in 19,118 patients, with a median Acute Physiology and Chronic Health Evaluation 3 score of 51. The mean CrC was 115.5 μmol/L (standard deviation: 100.2) compared to a CrP mean of 115 μmol/L (standard deviation: 100.7) (Pearson coefficient of 0.99). The mean difference between CrP and CrC was 0.49 μmol/L with 95% limits of agreement of -27 μmol/L and +28 μmol/L. Several biochemical variables were independently associated with the difference between tests (e.g., pH, potassium, lactate, glucose, and bilirubin), but their impact was small.

Conclusion: In critically ill patients, measurement of creatinine by POCT yields clinically equivalent values to those obtained by central laboratory measurement and can be easily used for more frequent monitoring of kidney function in such patients. These findings open the door to the use of POCT for the earlier detection of acute kidney injury in critically ill patients.