Accuracy of Point-of-Care Transdermal GFR Methodology

Chronic kidney disease (CKD) is typically staged using population-derived empirical equations to estimate glomerular filtration rate (GFR) based on serum creatinine and/or cystatin C. However, these estimated GFR (eGFR) equations can be inaccurate for an individual patient. Although plasma-derived GFR using an exogenous agent is the preferred methodology, the requirement for multiple blood samples and laboratory analysis limits its practical clinical utility. We have shown that the fluorescent molecule, relmapirazin, is an exogenous GFR tracer agent and its transdermal fluorescence detection at the point-of-care can assess a clinically relevant range of GFR across all human skin colors. In the current study, transdermal GFR (tGFR) was compared with the plasma-derived indexed GFR (nGFR) in a multicenter pivotal clinical study.

We evaluated 182 participants with normal eGFR to CKD stage 4 across all 6 Fitzpatrick Skin Scale (FSS) types. A sensor attached to the chest contained a light emitting diode and photodetector for transdermal fluorescence detection following i.v. administration of relmapirazin. The primary end point was percentage of tGFR values within 30% of nGFR (P₃₀).

P₃₀ of 94% (95% confidence interval [CI]: 89%-97%) was obtained for the entire cohort. P₃₀ was 96% and 92% for participants with GFR > or < 60 ml/min per 1.73 m², respectively. P₃₀ of 96% was for participants with FSS I to III and 90% with IV to VI.

The tGFR yielded a higher P₃₀ value than creatinine-based eGFR equations reported in the current literature. For the cohort subsets of CKD strata and FSS, all P₃₀ values observed were in the optimal range as established by the 2024 Kidney Disease: Improving Global Outcomes guideline.