#5228 ASSESSING ACCURACY OF POINT-OF-CARE CREATININE AND POTASSIUM TESTING IN A MULTI-ETHNIC SOUTH LONDON POPULATION
Authors: Brenner Ciaran Twomey , Bramham Kate , Mangahis Emmanuel , Mireku Vera , Oliveros Sheyenne , Villarhermosa Rachelle , Gama Rouvick 
Published: June 2023

Abstract

Background and Aims
Point-of-care (POC) testing allows rapid analysis of blood samples without delay of laboratory testing. For patients with chronic kidney disease (CKD), this allows for instant identification of changes in kidney function, such as acute kidney injury or hyperkalaemia, and assists in timely decision-making in outpatient or community settings (e.g. commencing or up-titrating medications dependent on renal function). It also provides an opportunity for early recognition of CKD in high-risk populations by providing screening in more convenient and trusted settings. To achieve these aims, it essential to confirm that POC systems can produce accurate results in real world settings with diverse patient populations. This pilot validation study assessed accuracy of the Siemens Epoc Blood Analysis System venous creatinine and potassium compared with laboratory assays in a diverse UK renal patient population.

Method
Venous blood samples from 57 patients, aged ≥ 18 years old and receiving care at a London teaching hospital, were analysed using the Siemens Epoc Blood Analysis System. POC-Creatinine (POC-Cr) and Potassium (POC-K) measurements were compared with laboratory (IDMS-traceable Siemens enzymatic and Roche) assays. Demographics (age, ethnicity and sex) were recorded for each patient. Passing-Bablock regression analysis were used to compare the results using both methods. Comparison between testing methods was assessed using a Bland-Altman plot. Limits of agreement were compared with CLIA criteria for acceptable performance for creatinine and potassium.

Results
The mean age was 55.6 ± 15.3 years old and 64.9% were male (n = 37). The majority of patients were of White (N = 23; 40.4%), Black (N = 21; 36.8%) or South Asian (N = 9; 15.8%) ethnicity respectively. Median POC-Cr was 216 μmol/L (interquartile range (IQR) 111, 396 μmol/L) versus median venous creatinine 212 μmol/L (IQR 114, 380 μmol/L). The median bias for creatinine was +1.0 (IQR -3.0, +8.0). Limits of agreement on Bland-Altman plot were +36.5μmol/L and – 34.4μmol/L (Figure 1). Overall, there remained a strong positive correlation between POC-Cr and IDMS-traceable enzymatic creatinine assays (R = 0.997; P&lt;0.0001) (Figure 2). Median POC-K was 4.3 mmol/L, IQR 4.0, 4.8 mmol/L versus median venous potassium 5.0, IQR 4.3, 5.3 mmol/L. The median bias for potassium was +0.4 (IQR +0.2, +0.5). Limits of agreement on Bland-Altman plot were +0.16mmol/L and – 0.91mmol/L (Figure 3). A strong positive correlation between POC-K and laboratory potassium assays was also confimed (R = 0.937; P&lt;0.0001) (Figure 4).

Conclusion
There was strong positive correlation between POC and laboratory analysis of venous creatinine, comparable to product literature (R = 0.997 vs 0.998). Limits of agreement were outside the CLIA criteria for acceptable performance (+/- 27μmol/L). POC and laboratory potassium levels were also strongly correlated and comparable to product literature (R = 0.937 vs 0.997). Limits of agreement were outside the CLIA criteria for acceptable performance (+/- 0.5mmol/L). This discrepancy is likely due to haemolysis in some blood samples and small sample size. Overall, this pilot study demonstrated a strong correlation between POC and laboratory testing. Larger scale evaluation is still required in a multi-ethnic population, prior to assessing feasibility in community-led protocolized pathways.