Nailfold Capillary Density and Kidney Injury in CKD

Background Microvascular dysfunction plays a key role in the development and progression of chronic kidney disease (CKD). Evaluation of capillaries by microscopy of the nailfolds may provide non-invasive insight into systemic microvascular health, but its relationship with kidney function, proteinuria, and kidney histopathology in individuals with CKD remains unknown. Methods We conducted a cross-sectional analysis of adults with CKD stages 2–5 (eGFR <90 mL/min/1.73 m 2 ) recruited from nephrology outpatient clinics at a single academic medical center between January 2023 and December 2025. Participants underwent assessment of 3 rd and 4 th finger nailfold microvascular structure and function using high-resolution video capillaroscopy at 100× magnification. The density of erythrocyte-perfused capillaries (capillaries/mm 2 ) was quantified at baseline, following release of arterial occlusion (hyperemic response), and during venous congestion using a deep learning–based image analysis pipeline. Associations between capillary density measures and kidney function (eGFR) and urine protein-to-creatinine ratio (uPCR) were evaluated using multivariable regression models. In a subset of participants Who underwent clinically indicated kidney biopsy, capillary density measures Were associated with histopathologic findings, including glomerulosclerosis (GS) and interstitial fibrosis and tubular atrophy (IFTA), using similar multivariable models . Results Among 189 CKD participants, mean (SD) age was 63 (16) years, 49% were female, 42% had diabetes, and 87% had hypertension. Mean (SD) baseline capillary density was 54 (15) capillaries/mm 2 . The mean eGFR was 41 (22) mL/min/1.73 m 2 and median (interquartile range [IQR]) uPCR was 0.31 [IQR 0.11 to 1.8] g/g. In adjusted models, higher capillary density was associated with higher GFR (β 0.33, 95% CI 0.25, 0.41) and lower uPCR (β -1.2, 95% CI -2.3, -0.6) independent of CKD risk factors. Results were similar evaluating capillary count at HA and OA. Among the subset of 36 participants with kidney biopsy data, lower capillary density was associated with greater GS and IFTA severity, which remained significant after adjustment for demographic factors, eGFR, and proteinuria. Conclusion Finger nailfold capillary density is associated with kidney function, proteinuria, and biopsy markers of chronic kidney injury among adults with CKD. Capillaroscopy may provide a non-invasive tool to identify vascular and interstitial damage above and beyond eGFR and proteinuria in CKD patients