Calcium and phosphorus metabolism in stable renal transplant recipients

This study sought to elucidate the status of calcium, phosphorus, and parathyroid hormone in patients following kidney transplant.

In this cross-sectional study, 20 renal transplant recipients were evaluated. For each patient, age, sex, time since transplant, and body weight were recorded. Inclusion criteria were age > 14 years and good allograft function defined as a serum creatinine level < 132.6 micromol/L for at least 6 months after transplant. Exclusion criteria were immunosuppressive therapy other than the standard triple regimen (cyclosporine, prednisolone, and mycophenolate mofetil or azathioprine) and use of any drug known to alter calcium hemostasis. Levels of 24-hour urine calcium, phosphorus, creatinine, and uric acid, as well as concentrations of hemoglobin, serum creatinine, calcium, and phosphorus were measured. To obtain a mean value of serum intact parathyroid hormone in transplant recipients at our center, serum intact parathyroid hormone levels were additionally quantitated in another group of 30 renal transplant recipients.

The mean hemoglobin level was 135.6 +/- 17.7 g/L, the mean serum creatinine level was 105.0 +/- 15.3 micromol/L, and the mean serum calcium and phosphorus levels were 2.25 +/- 0.17 mmol/L (normal range, 2.02-2.60 mmol/L) and 1.28 +/- 0.24 mmol/L (normal range, 0.81-1.61 mmol/L), respectively. The mean serum intact parathyroid hormone level was 33.17 +/- 14.67 ng/L (normal range, 10-60 ng/L). Mean 24-hour urine calcium and phosphorus values were 2.32 +/- 1.68 mmol/day (normal, 2.49-6.24 mmol/day) and 19.77 +/- 8.31 mmol/day (normal, 12.91-41.98 mmol/day), respectively. A positive correlation was found between serum calcium and alkaline phosphatase levels (r = +0.71, P = .006). Hemoglobin level was negatively correlated with serum phosphorus level (r = -0.65, P = .003) and sex (r = -0.57, P = .003) and positively correlated with urine creatinine levels (r = +0.69, P = .001).

Renal transplant recipients with stable allograft function may have normal serum calcium, phosphorus, and intact parathyroid hormone levels. However, presence of hypocalciuria and elevated serum alkaline phosphatase levels might imply impaired calcium metabolism in these patients.