Correlates of parathyroid hormone concentration in hemodialysis patients

Abstract

Background: The implications of chemical hyperparathyroidism on bone and mineral metabolism measures in maintenance hemodialysis (MHD) are not well known. We hypothesized that a higher serum intact parathyroid hormone (iPTH) level is associated with the higher likelihood of hyperphosphatemia, hyperphosphatasemia [high serum alkaline phosphatase (ALP) levels] and hypercalcemia.

Methods: Over an 8-year period (July 2001-June 2009), we identified 106 760 MHD patients with iPTH and calcium (Ca), phosphorous (P) and ALP data from a large dialysis clinic. Logistic regression models were examined to assess the association between serum iPTH increments and the likelihood of hyperphosphatemia (P ≥5.5 mg/dL), hypercalcemia (Ca ≥10.2 mg/dL) and hyperphosphatasemia (ALP ≥120 U/L).

Results: Patients were 61 ± 16 years old and included 45% women, 59% diabetics and 33% Blacks. Compared with an iPTH level of 100 to <200 pg/mL, patients with an iPTH level of 600-700, 700 to <800 and ≥800 pg/mL had 122% (OR: 2.22, 95% CI: 2.04-2.41), 153% (OR: 2.53, 95% CI: 2.29-2.80) and 243% (OR: 3.43, 95% CI: 3.22-3.66) higher risk of hyperphosphatemia, respectively, and had 109% (OR: 2.09, 95% CI: 1.93-2.26), 130% (OR: 2.30, 95% CI: 2.10-2.52) and 376% (OR: 4.76, 95% CI: 4.50-5.04) higher risk of hyperphosphatasemia, respectively. Compared with an iPTH level of 100 to <200 pg/mL, both the low iPTH (<100 pg/mL, OR: 2.45, 95% CI: 2.27-2.64) and the high iPTH (≥800 pg/mL: OR: 2.13, 95% CI: 1.95-2.33) levels were associated with hypercalcemia.

Conclusions: Higher levels of iPTH are incremental correlates of hyperphosphatemia and hyperphosphatasemia, whereas both very low and high PTH levels are linked to hypercalcemia. If these associations are causal, correction of hyperparathyroidism may have overarching implications on bone and mineral disorders in MHD patients.

Keywords: hemodialysis; serum alkaline phosphatase; serum calcium; serum intact parathyroid hormone; serum phosphorous.

FIGURE 1:

Flow chart of patient selection.

FIGURE 2:

Odds ratios for hyperphosphatemia (serum phosphorus ≥5.5 mg/dL) (A), high ALP level (≥120 U/L) (B) and high calcium level (≥10.2 mg/dL) (C) in 106 760 MHD patients in the baseline calendar quarter of the cohort for selected ranges of PTH. The case-mix model is adjusted for age, gender, race/ethnicity, categories of dialysis vintage, primary insurance, marital status, dialysis dose as indicated by K_t/V (single pool), residual renal function during the entry quarter, vascular access types, tobacco use, pre-existing of comorbidities including diabetes mellitus, AIDS, HIV-positive status, atherosclerotic heart disease, congestive heart failure, other cardiac disease, chronic obstructive pulmonary disease, cerebrovascular disease, peripheral vascular disease, history of hypertension, inability to ambulate and cancer. Malnutrition-inflammation complex syndrome (MICS)-adjusted model includes all of the case-mix covariates as well as body mass index, nPCR, serum levels of albumin, total iron-binding capacity, ferritin, creatinine, calcium, bicarbonate, white blood cell count, lymphocyte percentage and hemoglobin. Error bars represent SD.