Influence of dialysate calcium concentration and vitamin D on serum parathyroid hormone during repetitive dialysis

Effects of Lowering Dialysate Calcium Concentration on Mineral Metabolism and Parathyroid Hormone Secretion: A Multicentric Study

This prospective study was conducted with the aim of examining the efficacy of lowering dialysate calcium (dCa) in order to: (i) stimulate bone turnover in hemodialysis patients with biochemical signs of adynamic bone disease (ABD) (hypercalcemia, normal alkaline phosphatase and intact parathyroid hormone (iPTH) <150 pg/mL); and (ii) diminish hypercalcemia in patients with secondary hyperparathyroidism (sHPT) (hypercalcemia, high alkaline phosphatase and iPTH > 400 pg/mL), thus permitting the use of calcium-containing phosphorus binders and vitamin D metabolites. Patients were divided into: an ABD-treated group (24 patients), a sHPT-treated group (18 patients), an ABD-control group (12 patients) and a sHPT-control group (11 patients). For the ABD- and sHPT-treated patients, hemodialysis was conducted with dCa 1.5 mmol/L for three months and then with dCa 1.25 mmol/L for an additional three months, while in the control groups hemodialysis was conducted with dCa 1.75 mmol/L during the entire study. Reduction of dCa in patients with ABD caused a slight but insignificant decrease of Ca, but a significant and permanent increase of bone-specific alkaline phosphatase and intact parathyroid hormone level serum levels. Reduction of dCa in patients with sHPT slightly but insignificantly decreased Ca and intact parathyroid hormone level values. Nevertheless, this enabled the calcium-based phosphate binder dose to be raised and vitamin D3 metabolites to be introduced. Logistic regression analysis indicated that milder bone disease (both ABD and sHPT) was associated with more the favorable effect of dCa reduction. Thus, low dCa stimulated parathyroid glands and increased bone turnover in ABD patients, and enabled better control of mineral metabolism in sHPT patients.

Nocturnal but not short hours quotidian hemodialysis requires an elevated dialysate calcium concentration

Interest in quotidian (daily) hemodialysis (HD) is growing. Some advocate short-hours high-efficiency daily HD (SDH) and others long-hours slow-flow nocturnal HD (NH) while the patient is asleep, both being used 5 to 7 d/week. The London Daily/Nocturnal Hemodialysis Study was the first attempt to obtain data of SDH and NH that may be compared with conventional thrice weekly HD (CH). This was a 4-yr observational study designed to enter and follow 40 patients: 10 receiving SDH, 10 receiving NH, and 20 receiving CH. The CH patients were cohort control subjects matched for each SDH and NH patient by age, gender, comorbidity, and original dialysis modality (in-center, home, self-care, or satellite HD). All SDH and NH treatments were at home. Data collection to December 2001 was analyzed. Then enrollment had been completed and all patients had been followed for 15 mo, eight SDH plus six NH for 18 mo, seven SDH plus six NH for 21 mo, and seven SDH and five NH for 24 mo. This report gives data on calcium and phosphorus metabolism in these patients. All patients were initially dialyzed against a 1.25-mmol/L calcium bath. Predialysis serum calcium levels became lower in NH versus SDH patients by the first month and at 9 mo were 2.67 +/- 0.25 mmol/L (M +/- SD) in SDH, 2.40 +/- 0.16 mmol/L in NH, and 2.52 +/- 0.21 mmol/L in CH (SDH versus NH, P = 0.038; SDH versus CH versus NH, NS). Predialysis phosphorus levels were better controlled by NH than by SDH or CH, and with NH, all phosphate binders were discontinued. By 12 mo, a rise in bone alkaline phosphatase was seen in NH patients (but not in SDH or CH patients), which peaked at 15 to 18 mo (NH 191 IU/L +/- 70; SDH 82 +/- 34; CH 80 +/- 36; P < 0.002) and similarly with intact parathyroid hormone (iPTH) levels (NH 159 pmol/L +/- 75; SDH 13.1 +/- 10; CH 18 +/- 18; P < 0.00001). Because of these changes, the dialysate calcium concentration was increased to 1.75 mmol/L for the NH patients. Postdialysis calcium then rose to 2.57 +/- 0.21, and alkaline phosphatase and iPTH normalized completely by 21 mo. These observations prompted mass balance studies that showed that a 1.25-mmol/L calcium dialysate was associated with a mean net calcium loss of 2.1 mmol/h of dialysis time, whereas 1.75-mmol/L calcium dialysate provides a net gain of 3.7 mmol/h. In addition, the mass balance studies showed that phosphate removal by NH (43.5 +/- 20.7 mmol) was significantly (P < 0.05) higher than by SHD (24.2 +/- 13.9 mmol) but not by CH (34.0 +/- 8.7 mmol) on a per-treatment basis. With the increased frequency of treatments provided by quotidian dialysis, the weekly phosphorus removal (261.2 +/- 124.2 mmol) by NH was significantly higher than by SDH (P = 0.014) and CH (P = 0.03). This allowed the discontinuation of P binders in the NH group, which in turn eliminated approximately 8 g elemental Ca/wk oral intake. This, together with a 4 g elemental Ca/wk dialysate loss induced by a 1.25-mmol/L Ca bath, explains the changes in Ca, alkaline phosphatase, and iPTH seen in the NH patients. The SDH patients have weekly dialysis times similar to CH and still require P binders and do not become Ca deficient using 1.25-mmol/L Ca dialysate. With NH but not SDH, an elevated dialysate Ca concentration is required.

Biochemical effects of high dialysate calcium in hemodialysis patients with hyperparathyroidism: a 10 month study

In the past 15 years, there has been a trend to decrease dialysate calcium concentrations to prevent hypercalcemia. However, low dialysate calcium can provoke hyperparathyroidism. The time course of the effect of increasing dialysate calcium is not well characterized, and the effect on calcium-phosphate product is unclear. Therefore, we studied the effect of increasing dialysate calcium from 1.5 to 1.75 mM in 21 stable patients on hemodialysis who had serum phosphate of less than 2 mM and serum calcium of less than 2.4 mM. Over 10 months, parathyroid hormone levels fell from 39.6 to 16.6 pM (p < 0.0001), whereas serum calcium increased from 2.27 to 2.41 mM. There were no significant changes in serum phosphate or the calcium-phosphate product. Three patients became hypercalcemic when their parathyroid hormone levels were suppressed to less than 10 pM. We conclude that in carefully selected patients, increasing dialysate calcium can safely treat hyperparathyroidism with minimal risk of complications. This treatment has the advantage over the use of vitamin D therapy of being less expensive, independent of patient compliance, and less likely to cause increases in serum phosphate or calcium-phosphate product.

Low dialysate calcium in continuous ambulatory peritoneal dialysis: a randomized controlled multicenter trial. The Peritoneal Dialysis Multicenter Study Group

Hypercalcemia is a common complication in continuous ambulatory peritoneal dialysis (CAPD) patients treated with calcium-containing phosphate binders and using the standard dialysate calcium concentration of 3.5 mEq/L (SCa). Lowering the dialysate calcium was proposed to overcome this problem. The current randomized controlled multicenter study was designed to investigate efficiency and safety of a low calcium dialysate (2.00 mEq/L; LCa) compared with SCa (3.5 mEq/L) in CAPD patients. After an 8-week run-in period, 103 stable CAPD patients, 68 men, 35 women, aged 54.5 years (range, 20 to 77)) were randomly allotted to treatment with either LCa or SCa. All patients received calcium carbonate as oral phosphate binder to achieve serum phosphate levels < 6.2 mg/dL. If persistent hypercalcemia arose, CaCO3 was replaced by Al(OH)3 until normocalcemia was achieved. All patients received 0.25 microgram calcitriol/d. Parameters monitored included total and ionized serum calcium, serum phosphate, phosphate binder intake, incidence of hypercalcemia, serum aluminium, intact parathyroid hormone (1,84PTH), osteocalcin, alkaline phosphatase, bone mineral density and hand skeletal x-ray. Primary end points were (a) number of hypercalcemic episodes, (b) tolerated doses of calcium-containing phosphate binders, and (c) 1,84PTH. After 6 months of therapy, total and ionized calcium were lower in LCa patients (total Ca:9.6 v 10.08 mEq/L, P = 0.005; iCa: 4.76 v 5.15 mg/dL; P = 0.013). In the LCa group, significantly fewer episodes of hypercalcemia were recorded (total S-calcium > 10.8 mg/dL: LCa 24 v SCa 86 episodes; P < 0.005). Use of LCa permitted the administration of more CaCO3 (mean daily tablet number: LCa, 5.9 v SCa, 4.2; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

iPTH values during hemodialysis: role of ionized Ca, dialysis membranes and iPTH assays

The evolution of serum iPTH concentration during hemodialysis was studied in eight patients who were dialyzed with cuprophane (Cu) and polyacrylonitrile membranes (PAN) during two four-hour sessions. Ca+(+) concentration in the dialysate was 1.37 mM/liter. iPTH was measured with an intact hormone immunoradiometric assay (I), with two late (L1, L2) and one mid (M) carboxylterminal immunoassays at the beginning and end of hemodialysis, from the arterial and venous sides of the extracorporeal unit. Results are means +/- SD. Serum Ca+(+) increased during dialysis with Cu (1.26 +/- 0.08 vs. 1.33 +/- 0.03 mmol/liter, P less than 0.05, without any change in the concentration of iPTH measured with L1, L2 or M, but with a 50% decrease in iPTH measured with I (21.8 +/- 19.2 vs. 10.3 +/- 9.0 pmol/liter, P less than 0.05). Serum Ca+(+) increased similarly with PAN (1.25 +/- 0.10 vs. 1.34 +/- 0.04 mmol/liter, P less than 0.01), but there was a greater than 50% decrease in iPTH concentration measurements for all four assays (I: 17.2 +/- 17 vs. 7.6 +/- 8.3 pmol/liter, P less than 0.05; L1: 92 +/- 75 vs. 36 +/- 32 pmol/liter, P less than 0.05; L2: 312 +/- 289 vs. 126 +/- 128 pmol/liter, P less than 0.01; M: 926 +/- 1074 vs. 373 +/- 422 pmol/liter, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal osteodystrophy

Over the past decade important advances in our understanding of the pathophysiology and treatment of renal osteodystrophy have been made. In particular, the role of calcitriol deficiency in the genesis of hyperparathyroidism in early renal failure is now better understood. So too are the effects of aluminium on bone, and whereas the more florid aluminium related disease is now unusual the more subtle effects of aluminium are now being appreciated. There is still a major problem in the long-term treatment of hyperparathyroid bone disease. The reasons why parathyroid gland proliferation continues to occur on dialysis therapy require a better understanding of cellular events regulating hormone production and parathyroid cell replication. The case for early intervention with vitamin D is now strong but whether such an approach materially influences the long-term outcome is not yet established. Changes in the approach to treatment and in the modalities used for renal replacement therapy will continue to modify the nature of the bone disease.

Magnesium administration reverses the hypocalcaemia secondary to hypomagnesaemia despite low circulating levels of 25-hydroxyvitamin D and 1,25-dihydroxy vitamin D

The effect of parenteral administration of magnesium was studied in five patients with hypomagnesaemic hypocalcaemia. The initial metabolic state was characterized by a normal level of serum immunoreactive parathyroid hormone (iPTH), and by low or undetectable serum 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25 (OH)2D). A parathyroid response was elicited by the acute intravenous injection of magnesium chloride. In contrast, 1,25(OH)2D did not change up to 24 h after the injection. Intramuscular magnesium sulphate restored serum magnesium and calcium to normal, whereas iPTH was transiently increased. 25OHD remained low and unchanged. 1,25(OH)2D rose very slowly, but the correction of hypocalcemia began before any change in 1,25(OH)2D levels could be demonstrated. Thus, the early correction of hypocalcemia mainly depended on the restoration of an adequate parathyroid function independently of the secretion of 1,25(OH)2D.

[Hyperparathyroidism in hemodialysis patients: studies on parathyroid regulation and classification problems (author's transl)]

In a series of 22 patients undergoing chronic intermittent hemodialysis the response in secretion of parathyroid hormone (PTH) to an acute increase in serum calcium (Ca) concentration was studied. All patients had raised levels of predialysis PTH. Ca concentrations were measured by means of atomic absorption spectrophotometry and PTH concentrations were determined by radioimmunoassay. A close, significant, linear, negative correlation was demonstrated by regression analysis when Ca concentrations were correlated to changes in PTH, expressed as a percentage of the initial predialysis PTH value (100%). This finding supports the assumption that the function of the parathyroid gland at cellular level is similar in all patients, irrespective of very different predialysis PTH concentrations in peripheral blood. The results together with findings in literature were used to describe secondary hyperparathyroidism as a disease which shows typical phases during progression. Some still obscure phenomena of secondary hyperparathyroidism can be explained by discriminating between parathyroid function at a cellular and an organ level. The classification of hyperparathyroidism in regulative and autonomous forms only seems to be applicable when referred to the cellular level.

[Influence of vitamin D therapy on renal osteodystrophy in children (author's transl)]

Growth arrest and renal osteodystrophy is a major problem in renal insufficiency of children. The present report describes our experiences in managing renal osteodystrophy by using vitamin D3 for 24 months. Values in plasma of Ca, Mg, alkaline phosphatase, iPTH, 25-OH-D were determined regularly. Skeletal X-rays and analysis of iliac crest bone biopsies were obtained in each child. In treatment with vitamin D3 no hypercalcemia was seen despite high serum levels of 25-OH-D. Plasma-Ca, alkaline phosphatase, and iPTH normalized nearly. Radiographic abnormalities improved. Bone biopsies showed improvement in signs of secondary hyperparathyroidism and ostitis fibrosa, whereas osteomalacia remained unchanged. Osteoblast population showed a small reduction. No real increment in body growth was seen.

Secondary hyperparathyroidism in chronic renal failure. Pathophysiology and treatment

The secondary hyperparathyroidism of chronic renal failure is a result of many factors which result in chronic stimulation of parathyroid hormone secretion and secondary hyperplasia of the parathyroid glands. The secretion and metabolism of parathyroid hormone and its fragments in chronic renal failure are complex and only partially understood. Constant elevated levels of PTH contribute to bone disease and other clinical features of chronic renal failure. Calcium supplementation, high calcium dialysis, control of plasma phosphate and judicious use of the vitamin D metabolites can, to a large extent, prevent or control the development of secondary hyperparathyroidism. Subtotal parathyroidectomy or total parathyroidectomy with autotransplantation is indicated in certain cases, sometimes on an emergency basis. Prevention of postoperative hypocalcemia requires careful management. Successful renal transplantation is usually associated with gradual healing of the bone disease and slow, but sometimes incomplete involution of the parathyroid hyperplasia.

A possible role for propranolol in the treatment of renal osteodystrophy

The effect of propranolol upon parathyroid hormone (P.T.H) concentrations was investigated in patients undergoing chronic haemodialysis. 9 patients receiving propranolol for the treatment of hypertension or angina pectoris were compared with 25 similar patients not taking the drug. P.T.H. and alkaline phosphatase concentrations were lower in patients receiving propranolol and there was less radiological evidence of renal osteodystrophy in these patients. Prospective studies are needed to determine whether propranolol may be helpful as an adjunct to other therapy in reversing or preventing renal osteodystrophy.

The effect of dialysate calcium concentration on 1alpha-hydroxyvitamin D3 on skeletal calcium loss and hyperparathyroidism in haemodialysis patients

The response of hyperparathyroidism and skeletal calcium loss in haemodialysis patients to treatment with 1alpha-hydroxyvitamin D3 and a dialysate calcium concentration of 1.375 mmol/l was compared with the response to treatment with a dialysate calcium concentration of 1.375 or 1.75 mmol/l alone over a 6 month period. In patients treated with 1alpha-hydroxyvitamin D3 there was a significant rise in plasma calcium associated with a significant fall in plasma alkaline phosphatase and plasma parathyroid hormone as well as resolution of sub-periosteal erosions. In these patients there was a significant rise in the calcium content of the forearm assessed by neutron activation analysis in comparison to patients treated with a dialysate calcium concentration of 1.75 or 1.375 mmol/l alone. In patients treated with a dialysate calcium concentration of 1.375 or 1.75 mmol/l alone there was no significant change in the plasma calcium, alkaline phosphatase or parathyroid hormone after 6 months and in these patients subperiosteal erosions either did not change or became worse. No significant difference in the response in these two groups was observed. This study indicates that treatment of haemodialysis patients with 1alpha-hydroxyvitamin D3 is significantly more effective than treatment with a dialysate calcium concentration of 1.375 or 1.75 mmol/l alone in preventing progression of hyperparathyroidism and skeletal calcium loss.

Effects of high dialysate calcium concentration on bone remodelling, serum biochemistry, and parathyroid hormone in patients with renal osteodystrophy

The influence of a dialysate calcium concentration of 8.0 mg/100 ml (treatment period 2) vs. 7.0 mg/100 ml (treatment period 1) on plasma calcium, phosphorus, serum immunoreactive parathyroid hormone (iPTH), bone histology, intestinal calcium absorption, and calcium transfer across the dialysis membrane was investigated in six patients with renal osteodystrophy undergoing intermittent hemodialysis. During the periods 1 and 2, the plasma calcium changes before and after dialysis were not significantly different. A significant increase in mean postdialysis plasma calcium level was observed during both periods when compared to mean predialysis level. A significant, inverse relation was found between predialysis plasma calcium and the increase in plasma calcium during hemodialysis runs. Calcium transfer across the dialysis membrane and fractional intestinal absorption of calcium in the postdialysis state were determined in four out of the six patients. During period 2, calcium transfer was higher in all four patients but intestinal calcium absorption was moderately higher only in one and strikingly lower in the remaining three patients when compared to period 1. Although brought up to 8.0 mg/100 ml, this higher dialysate calcium significantly decreased the level of serum iPTH only in one out of the six patients; in this patient, osteoclast count, active resorption surface, and periosteocytic osteolysis decreased. In a second patient, although the level of serum iPTH seemed to decrease markedly osteoclastic and osteocytic resorption did not change. In the remaining four patients, the level of serum iPTH was unchanged and bone resorption parameters were found unchanged or aggravated. It is concluded that providing additional calcium (using a dialysate calcium concentration of 8.0 mg/100 ml), the goal of which was to decrease secondary hyperparathyroidism, proved to be successful only in one patient and failed to do so in the five others. Secondary hyperparathyroidism was even found aggravated in three of them. Thus, the use of a dialysate calcium concentration of 8.0 mg/100 ml did not result in any advantage over that of 7.0 mg/100 ml in five out of six patients studied.

The management of renal osteodystrophy

Hyperparathyroidism is the main cause of renal bone disease. At the moment its progress can be retarded by controlling plasma calcium and phosphate. But the prevention and cure of hyperparathyroidism without surgery eludes us. There is a suggestion that the administration of some metabolite of Vitamin D may be more successful. Osteomalacia on the other hand does not appear to be an important problem and is easily prevented and cured.

Effects of 25-hydroxycholecalciferol on bone lesions of children with terminal renal failure

Quantitative histology was performed on serial iliac crest biopsies obtained from 14 children with terminal renal failure. A long-term study on the comparative effects of vitamin D2 and 25-hydroxycholecalciferol [25-(OH)D3], in five patients with severe lesions of osteomalacia and/or osteitis fibrosa, demonstrated the efficiency of 25 to 200 mug/day of 25-(OH)D3 and the lack of therapeutic action of 345 to 685 mug/day of vitamin D2. In nine subjects with normal roentgenograms or minimal skeletal alterations, the first biopsy taken at the beginning of intermittent hemodialysis showed evidence of defective mineralization and/or lesions of resorption. Four of these children were treated with 25-(OH)D3 (25 to 50 mug/day) and calcium supplementation orally (0.5 to 1.5 g/day); five children received calcium orally (0.5 to 0.75 g/day) alone. Aggravation of bone lesions during intermittent hemodialysis was observed in patients treated with calcium supplements alone. In subjects who were given 25-(OH)D3, mineralization improved and marrow fibrosis disappeared. However, as the two groups of patients were different in composition and in the manner in which they were treated, it is difficult to state whether the beneficial effects observed were solely attributable to 25-(OH)D3 administration. 25-(OH)D3 therapy induced severe intoxication in two patients. A rise in plasma calcium concentration to 11.0 to 11.5 mg/100 ml was observed in two other patients. It is concluded that: a) pharmacologic doses of 25-(OH)D3 are highly effective in healing bone lesions of children with terminal renal failure; b) such treatment requires strict clinical surveillance as 25-(OH)D3 intoxication may occur even in anephric patients.