Posted November 1, 2011
Angela N. Bartley, MD
Creatinine, a waste product of muscle catabolism, is used to assess renal function, monitor the course of renal disease, and adjust renal function dependent drug dosages. Traditionally, renal function was measured using the glomerular filtration rate (GFR). A simpler alternative is using an estimated GFR (eGFR) by measuring endogenous plasma creatinine.1,2 The classic central laboratory method for measuring creatinine is based on its reaction with picric acid in the Jaffe reaction. There are other substances present in plasma including ketones, glucose, and bilirubin, collectively called pseudo-chromogens, that react with picric acid and thus interfere with this method. Newer enzymatic methods can eliminate the problems associated with pseudo-chromagens, and have made it possible to perform creatinine measurements on small or single-use devices at the point of care.
Point-of-care testing (POCT) methods have been shown in the past to be less precise than laboratory-based methods,4 but more recently developed tests have shown improvement. Depending on the POCT method, some devices show higher or lower values or biases in comparison to central laboratory methods and initial central laboratory validation is required to define these.5 The laboratory should perform correlation studies between POCT and central laboratory creatinine methods to compare results and adjust reporting appropriately. It is important that clinicians are aware that different devices and methodologies may give different results and that they work with laboratory personnel to adjust for those differences.
There are several situations that may justify rapid testing for creatinine using POCT. For example, in an imaging center, creatinine POCT may eliminate delays and improve patient throughput, satisfaction, and safety when there is potential exposure to nephrotoxic contrast agents.6 POCT can also be used to expedite chemotherapy dosage in oncology centers to avoid nephrotoxic affects. If physicians interpreting these test values are aware of creatinine method biases and limitations, they can use POCT to more efficiently and safely diagnose or treat patients. For physicians using creatinine POCT, the following additional practices are recommended:
- Develop and maintain a comprehensive quality assurance program, including operator training and competency assessment, quality control, proper equipment maintenance, reagent storage, periodic correlation of results with the central laboratory, and troubleshooting of significant discrepancies or errors.
- Work with the laboratory director and POCT coordinator to monitor testing and investigate any deviations, complaints, or incidents.
- Stay informed of recent innovations and limitations in POCT devices and creatinine testing.
- Consider concurrent central laboratory creatinine testing when results reach critical or predetermined levels.
- Require that patients with specific clinical risks or conditions have central laboratory creatinine testing.
POCT for creatinine is a relatively recent innovation, and physicians and testing centers should carefully weigh its advantages and drawbacks in certain applications. Direct doctor-to-doctor communication between pathologists and fellow clinicians could improve its effective use. Just as important, physicians performing POCT should know how their central laboratory and POCT creatinine methods compare to each other. This should be clearly communicated to the POCT sites and in protocols jointly developed to indicate when a central laboratory result should be used instead of POCT. It should also be considered that reporting both the eGFR calculation along with the POCT creatinine result may improve clinical decisionmaking.
- Levey AS, Stevens LA, Schmid CH, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604–612.
- Myers GL, Miller WG, Coresh J, et al. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clin Chem. 2006;52(1):5–18.
- Panteghini M. Enzymatic assays for creatinine: time for action. Clin Chem Lab Med. 2008;46(4):567–572.
- Skurup A, Kristensen T, Wennecke G; National Kidney Disease Education Program Laboratory Working Group. New creatinine sensor for point-of-care testing of creatinine meets the National Kidney Disease Education Program guidelines. Clin Chem Lab Med. 2008; 46(1):3–8.
- Shephard M, Peake M, Corso O, et al. Assessment of the Nova StatSensor whole blood point-of-care creatinine analyzer for the measurement of kidney function in screening for chronic kidney disease. Clin Chem Lab Med. 2010; 48(8):1113–1119.
- Korpi-Steiner NL, Williamson EE, Karon BS. Comparison of three whole blood creatinine methods for estimation of glomerular filtration rate before radiographic contrast administration. Am J Clin Pathol. 2009;132(6):920–926.
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NewsPath® Editor: C. Leilani Valdes, MD, FCAP
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