Calcium, phosphate, and PTH levels in the hemodialysis population: a multicenter study

Hyperphosphatemia is one of the main factors in the pathogenesis of secondary hyperparathyroidism. In addition, in dialysis patients elevated levels of phosphate and calcium times phosphate (Ca x P) ion product are associated with extraskeletal calcifications, as well as an increased risk of death. Cardiovascular calcifications may possibly be related to the high cardiovascular mortality seen in dialysis patients. In the USA the prevalence of hyperphosphatemia among dialysis patients is very high, over 60% of patients having serum P levels > 5.5 mg/dl, but no data are available for the Italian population, which follows different diet and dialysis schedules.

We looked at a random sample of 638 patients enrolled in 29 outpatient dialysis units in Southern Italy (Campania and Sicily). Data were centrally analyzed after extraction from a computerized database. In each patient the average of two or more values obtained in the six-month observation period (from Jan. 99 to June 99) was calculated. Mean age was 61.2 years (95% CI 59.9-62.5) years, dialytic age 72.2 months (95% CI 67.4-77.0).

Mean +/- SD (95% CI) levels of phosphate were 5.74 +/- 1.57 (5.62-5.86) mg/dl; total calcium 9.06 +/- 0.98 (8.98-9.14) mg/dl; Ca x P 51.4 +/- 14.4 (50.3-52.5) mg2/dl2; alkaline phosphatase was 167 +/- 119 (157-177) IU/L; intact parathyroid hormone (PTH) levels, available in a subset of 239 patients, were 318 +/- 413 (265-370) pg/ml. Among these patients 51.6% had serum P > 5.5 mg/dl, 36% > 6 mg/dl; Ca x P levels were > 55 mg2/dl2 in 35.5% of the population, 24% > 60 mg2/dl2; iPTH levels were < 100 pg/ml in 43%; 25.4% had hyperparathyroidism (defined as iPTH > 400 pg/ml), and only 19.5% of patients had PTH in the desired interval of 100 to 250 pg/ml.

Compared to data reported from the USA, mean levels of phosphate, Ca x P, and PTH seem better controlled in this Italian hemodialysis population. However, in a significant number of patients these parameters were still outside the normal range. Both over-suppression of PTH levels and hyperparathyroidism are present, although surprisingly the former was more frequent. Treatment of hyperphosphatemia should be more aggressive in hemodialysis patients; PTH levels are difficult to maintain in the desired range of 100-250 pg/ml.