Hypocalcemia and parathyroid hormone secretion in critically ill patients

Objective: To investigate possible causes of hypocalcemia and to assess par athyroid hormone (PTH) secretion in intensive care unit (ICU) patients. Design: Combined cross-sectional and prospective study. Setting: ICU in a university hospital. Patients: Thirteen patients with sepsis and 13 patients who underwent major surgery, interventions: None. Measurements and Main Results: Calcium metabolic indices were investigated during the first 24 hrs in the ICU and after 2 days. Eight of the surgical patients and five of the septic patients were subjected to a citrate/calciu m infusion on day 1 in the ICU, to study the dynamics of PTH secretion. The blood ionized calcium (Ca2+) concentration was generally low in the septic patients (mean +/- SD, 1.03 +/- 0.08 mmol/L; reference value, 1.10-1.30) a nd increased, hut not normalized, after 2 days. Hypocalcemia was only occas ionally seen in the surgical patients. In the septic patients, urinary excr etion of calcium was low; and, in both patient groups, elevated concentrati ons of two markers of bone resorption, deoxypyridinoline and ICTP (serum ca rboxy-terminal cross-linked telopeptide of type I collagen), were found. In cases of sepsis, the concentrations of proinflammatory cytokines were high (394 +/- 536 pg/mL for tumor necrosis factor-alpha and 5676 +/- 5190 pg/mL for interleukin-6, both normally <10-20), The Ca2+ concentration was inver sely related to tumor necrosis factor-alpha and interleukin-6 (r(2) = .35 - .42; p < .01), as well as to procalcitonin (r(2) = .71; p < .01), Despite normocalcemia in the surgical patients, serum PTH concentrations we re elevated in both patient groups (97 and 109 ng/L) (reference value, <55 ng/L), both on day 1 and day 3 in the ICU, The citrate/calcium infusion rev ealed an increased secretory response of PTH to lowered Ca2+ concentrations in both groups of patients (p < .05), when compared with matched healthy c ontrols. Conclusion: Hypocalcemia was common in septic ICU patients and was not the result of an increased urinary excretion of calcium or of an attenuated bon e resorption, but seemed related to the inflammatory response. An increased PTH secretion was found in both patient groups.