Creatinine measurement from finger stick dried blood spots with a routine chemistry analyzer for estimation of GFR

Objectives: Measuring creatinine levels is essential for assessing kidney function. However, traditional venous sampling poses challenges in terms of sample collection, storage, and transportation. Recently, dried blood spot (DBS) analysis has emerged as a potential alternative for measuring creatinine levels, although its clinical application remains limited. Creatinine measurements from DBS could facilitate chronic kidney disease screening, medication management, and at-home patient monitoring. Methods: Precision and hematocrit effect were assessed according to Clinical and Laboratory Standards Institute protocols to validate creatinine measurements in DBS. Subsequently, the protocol was applied in a method comparison involving 115 patients. Lastly, robustness was assessed by investigating creatinine stability over time and the influence of spotting effects. Results: Creatinine measurements in DBS resulted in low bias and correcting for hematocrit further improved accuracy. A comparison of creatinine and estimated glomerular filtration rate (eGFR) between venous plasma and finger stick DBS showed an R² of 0.97 and 0.86, respectively. Moreover, sensitivity and specificity for detecting decreased eGFR (<60mL/min/1.73m²) were 91 and 96%, respectively. Creatinine remained stable in DBS for up to a month at -20°C and 4°C, up to six days at 20°C, and one day at 37°C. Finally, spotting effects such as double spotting had negligible effects. Conclusions: In conclusion, creatinine from DBS can be analyzed using an automated high-throughput chemistry analyzer, enabling accurate eGFR classification. This method may support blood sampling at home for screening programs, patient follow-up, and medication management.