Cutaneous Microvascular Functional Reserve is Associated with Kidney Function and Histopathologic Injury in CKD: The MAP-CKD Study

Background: Microvascular dysfunction is a key contributor to the development and progression of chronic kidney disease (CKD), yet direct and reproducible assessment of microvascular function in clinical CKD populations remains limited. Laser Doppler flowmetry (LDF) provides a noninvasive, dynamic assessment of skin microvascular blood flow and may serve as a surrogate measure of systemic microvascular health. However, the extent to which LDF-derived measures relate to kidney function, proteinuria, and kidney histopathology in CKD remains unclear. Methods: We assessed cutaneous microvascular function in 150 participants with CKD (estimated glomerular filtration rate [eGFR] <90 mL/min/1.73 m²) using a standardized forearm LDF protocol. Baseline perfusion was recorded at ∼30°C, followed by local heating to 44 °C to induce hyperemia. The percentage change in perfusion unit (PU) was calculated and used to define microvascular functional reserve. Associations between LDF-derived measures with eGFR and urine protein-to-creatinine ratio (uPCR) were assessed using multivariable linear regression adjusted for demographic and clinical covariates. Unsupervised k-means clustering was performed to identify microvascular phenotypes based on resting PU and microvascular function reserve. Associations of LDF measures with glomerulosclerosis (GS) and interstitial fibrosis and tubular atrophy (IFTA) were evaluated in a subset of participants (n = 20) who underwent clinically indicated kidney biopsies. Results: Among 150 CKD participants, the mean (SD) age was 64 (14) years, 46% were female, 38% had diabetes, and 83% had hypertension. The mean eGFR was 42 (21) mL/min/1.73 m² and median uPCR was 0.21 (interquartile range (IQR) 0.11 to 1.20) mg/mg. Higher baseline PU (β = -12; 95% CI, -24 to -1) and reduced percentage change in PU (β = 7; 95% CI, 2 to 13) was associated with lower eGFR, independent of covariates. Baseline PU or percentage change in PU were not associated with uPCR. Unsupervised clustering identified four distinct microvascular phenotypes characterized by graded differences in resting perfusion and microvascular function reserve. Among participants with biopsy data, higher baseline PU and lower percentage change in PU were associated with greater severity of GS and IFTA. Conclusion: In persons with CKD, elevated resting perfusion and impaired microvascular functional reserve were associated with lower eGFR. These findings suggest that LDF-derived measures capture clinically relevant alterations in systemic microvascular function and may serve as a noninvasive biomarker of kidney function and underlying histopathologic injury in CKD.