Page 162 - Exploring the Potential of Self-Monitoring Kidney Function After Transplantation - Céline van Lint

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Chapter 7
The safety of self-monitoring
The accuracy of the creatinine device
One of the most important prerequisites for safe self-monitoring is the use of reliable measurement devices. When evaluating the performance of a measurement device, it is important to take the purpose of the measurement into consideration [43]. For measuring kidney function, one can distinguish diagnostic and monitoring purposes. A diagnostic purpose of measurement refers to the necessity to give an accurate indication of the current kidney function directly, for example before administering iodinated contrast media. In people with a decreased kidney function, iodinated contrast media can lead to contrast-induced nephropathy, one of the major causes of hospital- acquired acute kidney injury[44]. The accuracy of a single measurement is less important for a monitoring purpose, as one is interested in how kidney function develops over time. As the suitability of the StatSensor® for kidney transplant follow up had never been studied, we investigated whether the StatSensor® can be used both for detecting current renal function with a single creatinine measurement and for kidney function monitoring purposes. In chapter 4, we first evaluated the suitability of the StatSensor® to detect current renal function with a single measurement. Therefore, the traceability and exchangeability of StatSensor® results was compared to an isotope-dilution mass spectrometry (IDMS) traceable laboratory method, which is the gold standard for creatinine assays[45]. Our results showed that the StatSensor® creatinine device does not fulfil desirable nor minimum analytical performance criteria, which suggests that the StatSensor® is not suitable for detecting current renal function of kidney transplant patients with a single creatinine measurement. These findings are in agreement with previous studies that showed insufficient analytical validity of the StatSensor® in other populations [46, 47] compared to an IDMS traceable laboratory method. Improving the analytical performance of the StatSensor® would improve the potential for using the StatSensor® for diagnostic purposes.
As detection of rejection episodes after kidney transplantation mainly reflects a monitoring purpose, it is important to investigate whether a device is able to detect trends in sequential measurements. The reliability of a single test results is less critical for monitoring over time. For recently transplanted patients, clinicians are especially interested in sudden increases in serum creatinine of >10% as this requires further analysis or intensified follow-up. We investigated whether a >10% change in serum creatinine (as measured by the central IDMS-traceable laboratory method) can also be detected when using StatSensor® for trend monitoring. A reasonable correlation (R = 0.77) between changes detected by the central laboratory and the StatSensor® was found. The StatSensor® correctly identified an