Page 87 - Exploring the Potential of Self-Monitoring Kidney Function After Transplantation - Céline van Lint

Application of a creatinine device for trend monitoring 85
(RCVs) were calculated as 2.8 * (CVa +CVb ), where CVa means desirable analytical CV, and CVb means intra-individual biological CV (CVa =2.2%; CVb =4.3%; TEa =6.9%) [22].
For the evaluation of StatSensor®’s performance for determining creatinine trends in kidney transplant patients, a >10% increase in serum creatinine was considered to be clinically relevant. A general guideline is that an abrupt increase in the serum creatinine of greater than 50 percent should be promptly evaluated [23]. However, from professional experience, we know that an increase of 10% may indicate early symptoms of graft failure warranting further analysis or intensified follow-up of recently transplanted kidney patients. To calculate the degree of creatinine change, linear regression analysis was applied to analyze creatinine results generated during every 2-day interval with a maximum of five consecutive StatSensor® capillary creatinine measurements. The percentage creatinine change per day was obtained by dividing the slope by the average value (Figure 1). This calculation was also performed for the serum creatinine values determined by the central laboratory within the same time intervals. Only intervals which had at least four capillary creatinine values and three serum creatinine values available were selected. Agreement in levels of change as measured by the two methods was investigated by calculating the correlation between the percentage change in capillary creatinine and percentage change in venous serum creatinine for all selected 2-day intervals.
RESULTS
StatSensor®’s performance for detecting kidney function in kidney transplant patients
A total of 133 kidney transplant patients were included and 138 StatSensor® measurements were performed in duplicate (some patients visited the outpatient clinic twice during the period of inclusion). A mean difference of 20.21 μmol/L was found between the StatSensor® whole blood creatinine and the Roche Modular P800 serum creatinine (n=138) across the measuring range, with limits of agreement (defined as mean ±1.96 SD) varying between –58.8 and +34.1 μmol/L (see Sup- plemental Data, Figure 1).
To investigate equivalence of test results produced by StatSensor® and the central laboratory, 30 patients with StatSensor® creatinine results fitting into one of three categories (50–100, 100–200, >200 μmol/L) were selected. In addition, eight patients with the most marked differences between the duplicate capillary measurements (mean difference 42.5 ± 9.93, range 29 μmol/L) were selected. For each patient, a StatSensor® capillary whole blood creatinine result, a StatSensor® venous lithium heparin whole blood creatinine result, a venous lithium heparin plasma creatinine result as measured with the central laboratory method and a serum creatinine result as measured with the central
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