Kidney Function

Background: Determination of parathyroid hormone (PTH) level is the most commonly used surrogate marker for bone turnover in patients with stage 5 chronic kidney disease on dialysis therapy (CKD-5D). The objective of this study is to evaluate the predictive value of various PTH measurements for identifying low or high bone turnover rate.Study Design: Diagnostic test study.Settings & Participants: 141 patients with CKD-5D from 15 US hemodialysis centers.Index Tests: Intact PTH, PTH 1-84, and PTH ratio (ratio of level of PTH 1-84 to level of large carboxy-terminal PTH fragments).Reference Test or Outcome: Bone turnover determined using bone histomorphometry.Other Measurements: Demographic and treatment-related factors, serum calcium and phosphorus.Results: Patients presented histologically with a broad range of bone turnover abnormalities. In white patients with CKD-5D (n = 70), PTH ratio <1.0 added to intact PTH level <420 pg/mL increased the positive predictive value for low bone turnover from 74% to 90%. In black patients (n = 71), adding PTH ratio <1.2 to intact PTH level <340 pg/mL increased the positive predictive value for low bone turnover from 48% to 90%. Adding PTH ratio >1.6 to intact PTH level of 340-790 pg/mL increased the positive predictive value for high bone turnover from 56% to 71%.Limitations: Because the research protocol called for carefully controlled blood specimen handling, blood drawing and routine specimen handling might be less stringent in clinical practice. By limiting study participation to black and white patients with CKD-5D, we cannot comment on the roles of intact PTH, PTH 1-84, and PTH ratio in other racial/ethnic groups.Conclusion: In black patients with CKD-5D, the addition of PTH ratio to intact PTH measurements is helpful for diagnosing low and high bone turnover. In white patients with CKD-5D, it aids in the diagnosis of low bone turnover.

Background: Blood type AB kidney transplant candidates have the shortest waiting times, yet the current allocation system allows allocation of type A donor kidneys to type AB recipients.Study Design: United Network for Organ Sharing/Organ Procurement and Transplantation Network data between 1995 and 2004, retrospective observational study.Setting & Participants: 189,773 candidates listed for kidney-only transplant; 93,604 kidneys transplanted, 15,580 kidneys discarded.Predictor: Blood type and demographic/clinical variables.Outcomes & Measurements: The extent of disparities in waiting times and concurrent differences in recovery, discard, live donor, and deceased donor transplant rates.Results: Blood type O, A, B, and AB candidates constituted 48%, 34%, 14%, and 4% of the list, respectively. Live donor transplant rates were lowest for type AB candidates (13.4% vs 15.5%, 16.8%, and 15.2%; P < 0.001). On multivariate analysis, type AB candidates had a 1.5-fold greater chance of receiving deceased donor kidney transplants than blood group A candidates (95% CI, 1.45-1.55). Recovery rates of type AB kidneys were similar to those for other blood types, whereas discard rates of type AB kidneys were significantly higher (adjusted OR [aOR], 1.71; 95% CI, 1.56-1.89) for both expanded criteria (aOR, 1.78; 95% CI, 1.52-2.09) and standard criteria donors (aOR, 1.67; 95% CI, 1.48-1.89).Limitations: Observational data. Potential confounding from unmeasured covariates.Conclusion: Allocation of type A kidneys to type AB recipients not only increases disparities in waiting times between these 2 groups; but concurrent with the shorter waiting times for type AB candidates, there is suboptimal use of type AB deceased donor and living donor kidneys.

Background: Vascular calcification contributes to cardiovascular disease in patients with chronic kidney disease (CKD). Few studies have addressed interventions to decrease vascular calcification; however, experimental studies report benefits of bisphosphonates. Recent studies of hemodialysis patients also suggest benefits of bisphosphonates on vascular calcification; however, no study exists in nondialysis patients with CKD.Study Design: We conducted a randomized controlled trial to determine the effect of bisphosphonates on vascular calcification in patients with CKD.Setting & Participants: 51 patients with CKD stages 3-4 were recruited from a hospital outpatient setting; 50 were treated with study medication.Interventions: Patients were randomly assigned to either alendronate, 70 mg (n = 25), or matching placebo (n = 25), administered weekly.Outcomes: The primary outcome was change in aortic vascular calcification after 18 months. Secondary outcomes included superficial femoral artery vascular calcification, arterial compliance, bone mineral density (BMD), renal function, and serum markers of mineral metabolism.Measurements: At baseline and 12 and 18 months, computed tomography, pulse wave velocity using SphygmoCor (AtCor Medical, PWV Inc, www.atcormedical.com), and dual-energy x-ray absorptiometry were performed to measure vascular calcification, arterial compliance, and BMD, respectively. Analysis was by intention to treat, with a random-effect linear regression model to assess differences.Results: 46 patients completed the study (24 alendronate, 22 placebo); baseline mean age was 63.1 ± 1.8 years, estimated glomerular filtration rate was 34.5 ± 1.4 mL/min/1.73 m2, 59% had diabetes, and 65% were men. 91% had aortic vascular calcification at the start and 78% showed progression. At 18 months, there was no difference in vascular calcification progression with alendronate compared with placebo (adjusted difference, −24.2 Hounsfield units [95% CI, −77.0 to 28.6]; P = 0.4). There was an increase in lumbar spine BMD (T score difference, +0.3 [95% CI, 0.03-0.6]; P = 0.04) and a trend toward better pulse wave velocity (−1 m/s [95% CI, −2.1 to 0.1]; P = 0.07) with alendronate. Femoral BMD was similar between groups. There was a nonsignificant decrease in kidney function in patients on alendronate therapy compared with placebo (−1.2 mL/min/1.73 m2 [95% CI, −4.0 to 1.7]).Limitations: Small sample size and baseline differences, especially with aortic vascular calcification, may have diminished any potential difference between groups.Conclusions: Unlike previous studies of hemodialysis patients, alendronate did not decrease the progression of vascular calcification compared with placebo in patients with CKD during 18 months.