Assessment of tubular reabsorption of phosphate as a surrogate marker for phosphate regulation in chronic kidney disease.

BACKGROUND/AIMS: Fibroblast growth factor 23 (FGF23) and soluble α-Klotho are emerging potential biomarkers of phosphorus and vitamin D metabolism which change in concentration in early chronic kidney disease (CKD) in order to maintain normal phosphorus levels. Tubular reabsorption of phosphate (TRP) has been commonly used to assess renal tubular phosphate transport. The aim of this study was to evaluate the usefulness of TRP as a surrogate marker of parameters of CKD-mineral bone disease (CKD-MBD) in CKD. METHODS: A cross-sectional study was performed in 93 stable patients with predialysis CKD stage 1-5. In all patients, TRP, estimated glomerular filtration rate (eGFR), calcium, phosphate, intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, serum FGF23 and urine soluble α-Klotho levels were measured. RESULTS: As renal function declined, TRP significantly decreased (P < 0.001; r = 0.763) and both iPTH and serum FGF23 increased (P < 0.001; r = -0.598, P < 0.001; r = -0.453, respectively). The prevalence of hyperphosphatemia, secondary hyperparathyroidism, FGF23 excess and abnormal TRP increased progressively with declining eGFR. Although TRP level changed later than FGF23, abnormal levels of both TRP and FGF23 were observed earlier than changes in iPTH and serum phosphate. Decreased TRP was found to be independently associated with decreased eGFR and increased iPTH but was not associated with urine soluble α-Klotho or serum FGF23 level in multiple linear regression analysis. CONCLUSION: TRP is a simple, useful and cost-saving surrogate marker of the assessment of altered mineral metabolism in CKD patients and can be used as an alternative to serum FGF23, especially for mild to moderate renal insufficiency.

Clinical usefulness of BK virus plasma quantitative PCR to prevent BK virus associated nephropathy.

The present study investigated the clinical usefulness of plasma real-time polymerase chain reaction (PCR) (plasma-PCR) in the prevention of BK virus-associated nephropathy (BKVAN). First, we investigated the diagnostic value of plasma BK-PCR, urine BK-PCR, and urine cytology for the prediction of BKVAN retrospectively. Then we designed a prospective study of regular plasma-PCR monitoring and pre-emptive immunosuppression (IS) reduction based on the result. In the retrospective cohort, the prevalence of BKVAN was 3.7% (14/379) and the positive rate of decoy cells, urine-PCR (>1 × 10(10) copies/ml), and plasma-PCR (>1 × 10(4) copies/ml) was 18.6%, 11.1%, and 5.5%, respectively. Plasma-PCR was superior to urine-PCR or urine cytology in specificity and positive predictive value for detection of BKVAN. In prospective study, regular monitoring of plasma-PCR detected significant BKV viremia in 8.3% (12/145) and BKVAN in 1 patient (0.6%). After IS reduction, BKV viremia was eliminated in 91.6% (11/12) within 103 days (25-254). In patients with viremia, the frequency of acute rejection did not increase and allograft function did not differ significantly compared with those in patients without viremia during the first year post-transplant (P > 0.05, in both). Plasma-PCR is useful to predict an increased risk for BKVAN, and regular monitoring is effective to prevent the development of BKVAN.