Chronic kidney disease (CKD) is frequently accompanied by vascular injury and microcirculatory abnormalities. Skin microcirculation, including the finger nailfold, is considered a window onto systemic microvascular structure and function. Prior capillaroscopy research has emphasized rheumatic and dialysis populations; efficient, noninvasive measures of microcirculatory change in non-dialysis CKD remain limited. This study evaluated whether nailfold capillaroscopy indexes associate with renal function parameters in non-dialysis CKD patients.
This was a retrospectively registered observational study conducted at Xuzhou Medical University Affiliated Hospital. The trial was registered at ClinicalTrials.gov (NCT03682952) and approved by the local ethics committee (XYFY2018-KL034–01). All participants provided written informed consent. Data were accessed for research between 01/10/2018 and 31/12/2020 as reported in the source.
The study enrolled 68 non-dialysis CKD patients and 41 healthy controls. After exclusions (five CKD patients excluded for uncontrolled blood pressure, nailfold skin injury, or excessive nailfold cuticle thickness), 63 CKD patients remained in the CKD group and 41 individuals formed the control group. CKD inclusion required non-dialysis status and blood pressure control (systolic ≤140 mmHg, diastolic ≤90 mmHg). Exclusion criteria removed participants with comorbid conditions likely to affect systemic circulation or vascular function (including cardiovascular, cerebrovascular, respiratory, endocrine, rheumatic immune diseases, infection, shock, dehydration, need for urgent dialysis, and similar emergencies).
Nailfold capillaroscopy was performed after participants rested for 15–20 minutes in a warm room. Pine and cypress oil were applied to the fourth finger nailfold to enhance visualization. Images were captured and 20 parameterized indexes were evaluated, including: clarity integral, capillary number integral, input and output branch diameter integrals, capillary top diameter integral, capillary length integral, crossed and abnormal capillary numbers, velocity of blood flow integral, erythrocyte aggregation integral, white microthrombus and white blood cell integrals, color of blood integral, perivascular exudation integral, capillary hemorrhage integral, subpapillary venular plexus integral, and others. The authors reported clear, wavy capillaries with normal shape and good flow in controls; CKD progression associated with blurred images, reduced capillary number, poorer flow, and in severe cases flattened papillae and abnormal capillary morphology.
The study used the Niu Tian integral method to produce a weighted composite integral and a five-degree grading of nailfold microcirculation. Thresholds for mild, moderate, and severe abnormality were defined by combinations of parameter changes or total integral scores (for example, total integral ≥8 or marked capillary loss or heavy erythrocyte accumulation defined severe abnormality). The source includes full criteria for the grading scheme and the 20-index scoring system.
SPSS 22.0 was used. Continuous variables fitting a normal distribution were reported as mean ± SD and compared by independent-samples t tests; non-normally distributed variables were described as median (quartiles) and compared by Mann–Whitney U tests. Sex differences were assessed by chi-square. Spearman correlation analyzed relationships between renal function markers (Scr, BUN, cystatin C, eGFR, CKD stage, hemoglobin) and meaningful nailfold indexes. Multiple linear regression models adjusted for age, blood pressure, hemoglobin, and CKD etiology evaluated independent associations, with separate models using capillary number integral and subpapillary venular plexus integral as dependent variables. P < 0.05 denoted statistical significance.
Sex, age, systolic blood pressure, and diastolic blood pressure did not differ significantly between CKD patients and controls. Hematological and renal function markers differed: serum creatinine (Scr), blood urea nitrogen (BUN), and cystatin C were higher in the CKD group, while estimated glomerular filtration rate (eGFR) and hemoglobin (Hb) were higher in controls (all P < 0.001 as reported).
Among the 20 capillaroscopic indexes, the CKD group exhibited increases in capillary number integral, output branch diameter integral, capillary top diameter integral, crossed capillary number integral, velocity of blood flow integral, erythrocyte aggregation integral, perivascular exudation integral, and capillary hemorrhage integral relative to controls. Conversely, capillary length integral, color of blood integral, and subpapillary venular plexus integral were decreased in CKD patients (P < 0.05 for all comparisons noted in the source). The authors designate the set above as the meaningful indexes.
Within the CKD group, Spearman correlation analyses showed that Scr, BUN, cystatin C, and CKD stage correlated positively with capillary number integral, while eGFR correlated negatively with capillary number integral. For the subpapillary venular plexus integral, Scr, cystatin C, and CKD stage correlated negatively, and eGFR correlated positively. These relationships were reported with statistical significance (P < 0.05) in the source.
Adjusted multiple linear regression models identified independent associations: Scr, cystatin C, and CKD stage were independently and positively associated with the capillary number integral; eGFR and hemoglobin were independently and negatively associated with the capillary number integral. For the subpapillary venular plexus integral, Scr, cystatin C, and CKD stage were independently and negatively associated, while eGFR was independently and positively associated. Age, blood pressure, hemoglobin level, and CKD etiology were included as covariates in these models as reported.
The reported data suggest that worsening renal function in non-dialysis CKD associates with increased capillaroscopic scores reflecting reduced capillary number and alterations consistent with impaired subpapillary venous plexus relaxation. The authors propose that nailfold capillaroscopy may provide a noninvasive, quantitative window into peripheral microcirculatory changes that correlate with renal dysfunction.
The source states the study is observational and retrospective in registration; details such as causal inference are limited by study design. The authors report that all relevant data are within the paper. Funding sources and ethical approvals are described in the source. No competing interests were declared by the authors in the report.