The use of point of care testing for the diagnosis of chronic kidney disease

Currin, Sean
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Article 1 Introduction: The prevalence of chronic kidney disease is rising rapidly in low- and middle-income countries. Serum creatinine and estimation of glomerular filtration rate (GFR) are critical diagnostic tools, yet access to centralised laboratory services remains limited in primary care resource-limited settings. The aim of this study was to evaluate point-of-care (POC) technologies for serum creatinine measurement and to compare their performance to a gold standard measurement using iohexol mGFR. Methods: POC creatinine was measured using iSTAT® and StatSensor® devices in capillary and venous whole blood, and laboratory creatinine was measured using the compensated kinetic Jaffe method in 670 participants from a rural area in South Africa. GFR estimating equations (CKD-EPI and MDRD) for POC and laboratory creatinine were compared to iohexol mGFR. Results: Calculated GFR for laboratory and POC creatinine measurements overestimated GFR (positive bias of 1.9 - 34.1ml/min/1.73m2). However, all POC devices had less positive bias than the laboratory Jaffe method (1.9 - 14.7 vs 34.1 for MDRD, and 8.4 – 19.9 vs 28.6 for CKD-EPI). Accuracy within 30% of mGFR ranged from 0.56 – 0.72 for POC devices and from 0.36 – 0.43 for the laboratory Jaffe method. POC devices showed wider imprecision with coefficients of variation ranging from 4.6 - 10.2% compared to 3.5% for the laboratory Jaffe method. Conclusion: POC eGFR showed improved performance over laboratory Jaffe eGFR, however POC devices suffered from imprecision and large bias. The laboratory Jaffe method performed poorly, highlighting the need for laboratories to move to enzymatic methods to measure creatinine. Article 2 Background: the prevalence of chronic kidney disease (CKD) is predicted to rise over the next few decades. In resource-limited settings access to central laboratory services is limited. Point-of-care (POC) urine dipstick testing offers the potential to detect markers of kidney damage (albuminuria) as well as markers of other disease processes. We evaluated the diagnostic accuracy of the semiquantitative albumin-creatinine ratio (ACR) Sysmex UC-1000 POC urine dipstick system as well as the extent of other abnormal dipstick findings in urine. Methods: 700 participants from a rural area in South Africa were screened for albuminuria. A spot urine sample was used to measure POC and central laboratory ACR. We determined the sensitivity, specificity, positive predictive value and negative predictive value of the POC ACR, and recorded dipstick parameters. Results: the prevalence of albuminuria was 11.6% (95%CI; 9.3 – 14.2). Those with albuminuria had higher mean diastolic (82 vs 79mmHg, p=0.019) and systolic (133 vs 128mmHg, p=0.002) blood pressures and a higher proportion of diabetes mellitus (17.6 vs 4.9%, p<0.001). The sensitivity of the POC ACR system was 0.79, specificity 0.84, positive predictive value 0.39 and negative predictive value 0.97. The sensitivity improved to 0.80, 0.85, 0.85 and 0.89 in those with elevated blood pressure, diabetes mellitus, HIV positive status, and those 65 years and older, respectively. Abnormalities other than albuminuria were detected in 240 (34.3%) of the samples; 88 (12.6%) were positive for haematuria, 113 (16.1%) for leucocytes, 66 (9.4%) for nitrites and 27 (3.9%) for glycosuria. Conclusion: our study shows that POC ACR has good negative predictive value and could be used to rule out albuminuria when screening for CKD. Additionally, a high proportion of participants had other urine abnormalities detected with dipsticks which may reflect kidney disease or co-morbid untreated genitourinary pathology such as urinary tract infections or endemic schistosomiasis with important implications for CKD.
A research report submitted in fulfilment of the requirements for the degree of Master of Medicine in Chemical Pathology to the Faculty of Health Sciences, School of Pathology, University of the Witwatersrand, Johannesburg, 2021