Femoral bone mineral density reflects histologically determined cortical bone volume in hemodialysis patients

We evaluated the associations between dual energy X-ray absorptiometry (DXA) and histologically determined cancellous and cortical bone volume by controlling for vascular calcifications and demographic variables in hemodialysis (HD) patients. Femoral bone mineral density (f-BMD) was associated with cortical porosity.

INTRODUCTION

Assessment of bone mass in chronic kidney disease patients is of clinical importance because of the association between low bone volume, fractures, and vascular calcifications. DXA is used for noninvasive assessment of bone mass whereby vertebral results reflect mainly cancellous bone and femoral results reflect mainly cortical bone. Bone histology allows direct measurements of cancellous and cortical bone volume. The present study evaluates the association between DXA and histologically determined cancellous and cortical bone volumes in HD patients.

METHODS

In 38 HD patients, DXA was performed for assessment of bone mass, anterior iliac crest bone biopsies for bone volume, and multislice computed tomography for vascular calcifications.

RESULTS

While lumbar bone mineral density (l-BMD) by DXA was not associated with histologically measured cancellous bone volume, coronary Agatson score showed a borderline statistically significant association (P = 0.055). When controlled for age and dialysis duration, f-BMD by DXA was associated with cortical porosity determined by histology (P = 0.005).

CONCLUSIONS

The usefulness of l-BMD for predicting bone volume is limited most probably because of interference by soft tissue calcifications. In contrast, f-BMD shows significant association with cortical porosity.

A calcimimetic agent lowers plasma parathyroid hormone levels in patients with secondary hyperparathyroidism

BACKGROUND

The calcimimetic agent R-568 lowers plasma parathyroid hormone (PTH) levels in hemodialysis patients with mild secondary hyperparathyroidism, but its efficacy in those with more severe secondary hyperparathyroidism has not been studied.

METHODS

Twenty-one patients undergoing hemodialysis three times per week with plasma PTH levels between 300 and 1200 pg/mL were randomly assigned to 15 days of treatment with either 100 mg of R-568 (N = 16) or placebo (N = 5). Plasma PTH and blood ionized calcium levels were measured at intervals of up to 24 hours after oral doses on days 1, 2, 3, 5, 8, 11, 12, and 15.

RESULTS

Pretreatment PTH levels were 599 +/- 105 (mean +/- SE) and 600 +/- 90 pg/mL in subjects given R-568 or placebo, respectively, and values on the first day of treatment did not change in those given placebo. In contrast, PTH levels fell by 66 +/- 5%, 78 +/- 3%, and 70 +/- 3% at one, two, and four hours, respectively, after initial doses of R-568, remaining below pretreatment values for 24 hours. Blood ionized calcium levels also decreased after the first dose of R-568 but did not change in patients given placebo. Despite lower ionized calcium concentrations on both the second and third days of treatment, predose PTH levels were 422 +/- 70 and 443 +/- 105 pg/mL, respectively, in patients given R-568, and values fell each day by more than 50% two hours after drug administration. Predose PTH levels declined progressively over the first nine days of treatment with R-568 and remained below pretreatment levels for the duration of study. Serum total and blood ionized calcium concentrations decreased from pretreatment levels in patients given R-568, whereas values were unchanged in those given placebo. Blood ionized calcium levels fell below 1.0 mmol/L in 7 of 16 patients receiving R-568; five patients withdrew from study after developing symptoms of hypocalcemia, whereas three completed treatment after the dose of R-568 was reduced.

CONCLUSIONS

The calcimimetic R-568 rapidly and markedly lowers plasma PTH levels in patients with secondary hyperparathyroidism caused by end-stage renal disease.

Intermittent oral 1alpha-hydroxyvitamin D2 is effective and safe for the suppression of secondary hyperparathyroidism in haemodialysis patients. 1alphaD2 Study Group

Calcitriol and alfacalcidol are useful in suppressing parathyroid hormone (PTH) in haemodialysis patients, but hypercalcaemia and hyperphosphataemia are frequent. The vitamin D analogue, 1alpha-hydroxyvitamin D2 (1alphaD2), has a higher therapeutic index in animal models. Previously, 1alphaD2, 4 microg/day or 4 microg/haemodialysis, lowered iPTH to the target range in 87.5% of 24 haemodialysis patients with moderate to severe secondary hyperparathyroidism (plasma iPTH, 359-1521 pg/ml). The incidences of hypercalcaemia (serum Ca>2.8 mM) or hyperphosphataemia (serum P>2.23 mM) were low. Later, 10 of these patients were re-treated with 1alphaD2, initial dose, 10 microg, thrice weekly with haemodialysis. The iPTH was suppressed as readily, and there was no greater incidence of hypercalcaemia and hyperphosphataemia. Based on these data, a large, multicentre study is ongoing in California and Tennessee/Mississippi, using 1alphaD2 in haemodialysis patients with iPTH >400 pg/ml. In this and the earlier studies, only calcium-based phosphate binders were used to control serum phosphorus. The initial dose, 10 microg thrice weekly with haemodialysis, is adjusted to maintain a target iPTH within the range of 150-300 microg/ml; the final dose range is 2.5-20 microg per haemodialysis. The protocol includes 8 weeks of wash-out with no vitamin D, 16 weeks of open label treatment period with 1alphaD2, and finally 8 weeks of randomized double blinded treatment with either continued 1alphaD2 or placebo. Forty two patients from California and 38 from Tennessee/Mississippi have completed 16 weeks of open label treatment. In California, iPTH declined from 832+/-95 pg/ml at baseline to 222+/-71 pg/ml at the nadir and to 477+/-117 pg/ml at week 16 of the treatment. In Tennessee/Mississippi, the iPTH declined from 977+/-65 pg/ml to 286+/-42 pg/ml at the lowest point and to 493+/-79 at the end of the treatment. Plasma iPTH reached or fell below the target range in 84% of the 80 patients completing open treatment. Asymptomatic hypercalcaemia (serum Ca>2.8 mM) increased from 0.3 episodes/100 weeks during wash-out to 3.6 episodes/100 treated weeks in California and from 0 to 3.7 episodes in Tennessee/Mississippi. In California and Tennessee, the episodes of hyperphosphataemia (serum P>2.2 mM) increased from 5.0 and 5.0 episodes per 100 patient/week during wash-out to 10.1 and 10.9 episodes/100 treatment weeks, respectively, with 1alphaD2 treatment. There were no adverse events in association with 1alphaD2 treatment. Thus, oral 1alphaD2 is safe and highly effective for the treatment of secondary hyperparathyroidism.

Carbamylated hemoglobin in prerenal azotemia

Carbamylated hemoglobin (Carb Hb) levels were measured in 16 patients with a documented transient rise in BUN due to prerenal azotemia, in whom BUN levels before and after the episode were normal. They were compared with 13 controls. Carb Hb was expressed as carbamyl valine concentrations, which were significantly higher in the patients (166 micrograms/g Hb) than in controls (95.3 micrograms/g Hb, p < 0.01). The mean maximum BUN level in the patients was 51.8 +/- 23.9 mg/dl. There was a significant correlation between the product of mean BUN level times the number of days of BUN elevation, and the Carb Hb level (r = 0.5197; p < 0.05). There was no correlation between Carb Hb and either mean BUN level or maximum BUN level. Elevated Carb Hb was seen after a minimum of 4 days' BUN elevation. Four patients had no elevation of Carb Hb despite elevated BUN levels.

CONCLUSION

Carb Hb may be elevated after a minimum of 4 days' transient BUN elevation; Carb Hb is not useful in differentiating between mild acute renal failure and prerenal azotemia.

Persistence of antibodies to hepatitis C virus in a chronic hemodialysis population

In order to evaluate the persistence of antibodies against hepatitis C virus (HCV) in a chronic hemodialysis population, we studied 151 HBsAg-negative patients. Anti-HCV titers were evaluated every 3 months over 1 year, and the serum alanine aminotransferase/serum aspartate aminotransferase ratio monthly from the start of hemodialysis. The anti-HCV titers (ELISA C100-3) remained stable in 127 patients and fluctuated in 24, without an evident correlation with hepatic function. Using our criteria, we found 85 patients with non-A, non-B hepatitis, 57 of them with biochemical criteria of chronic hepatic disease. There was a strong correlation between antibodies to HCV and non-A, non-B hepatitis (chi 2; p < 0.05) which was more marked in those patients with biochemical criteria of chronic hepatic disease (chi 2; p < 0.001). We concluded that the anti-HCV titer is reliable as a long-term marker of hepatitis C virus infection.