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Background Endothelial dysfunction is the primary step for the development of CKD-related cardiovascular disease. Early prediction and management can influence patient survival. Serum testing of FGF 23 hormone and urinary phosphate excretion were studied as predictors of all-cause cardiovascular morbidity in CKD patients; however, their relation to endothelial dysfunction is controversial. A combination of both in one index is hypothesized to increase their sensitivity in detecting endothelial dysfunction, especially in the early stages of CKD before the dominance of hyperphosphatemia, the original risk. Methods A cross-sectional comparative analysis between thirty CKD stage 3 patients and sixty stage 4–5 CKD patients was conducted. All patients were tested for markers of mineral bone disorders including serum FGF 23 and 24-h urinary phosphate excretion. A combination of both in one index (nephron index) is calculated and hypothesized to correlate with nephron number. Endothelial dysfunction was assessed by measuring the post-occlusion brachial flow-mediated dilatation (FMD). Results In univariate and multivariate regression analyses, the nephron index was the only predictor of endothelial dysfunction in individuals with stage 3 CKD (r = 0.74, P 0.01). This was not applied to stage 4–5 CKD patients where serum phosphorus (r = − 0.53, P 0.001), intact PTH (r = − 0.53, P 0.001), uric acid (r = − 0.5, P 0.001), and measured GFR (r = 0.59, P 0.001) were the highest correlates to FMD; the Nephron index had the weakest correlation (r = 0.28, P = 0.02) and is not predictive of endothelial dysfunction. Conclusion Nephron index calculation showed better correlation with endothelial dysfunction than using any of its determinants alone in early stages of CKD when FGF 23 levels are just beginning to rise. In advanced CKD patients, hyperphosphatemia, hyperparathyroidism, hyperuricemia, and measured GFR are more reliable than nephron index.

Solid-organ transplant is the treatment of choice for all patients with end-stage diseases. Long-term graft function and survival rely on suitable immunosup-pressive treatment to prevent rejection. Besides this desired effect, a reduced immunocompetence in the transplant recipient increases the risk of developing infectious diseases and malignancies. An ideal biomarker should be sensitive, allow early visibility, be accessible in peripheral blood, and be associated with a known mechanism. Torque teno virus or transfusion transmitted virus is a virus that has gained attention as a possible marker of immune function. This virus rarely causes disease in healthy individuals, but torque teno viral load in immunosuppressed patients is shown to be higher than in healthy controls. Replication of torque teno virus is inversely correlated with number and especially functions of T lymphocytes. Torque teno virus could join the current list of predictive biomarkers in transplantation to detect whether the patient is over- or under-immunosuppressed. More studies are needed to confirm or disprove this possibility.