PTH and hyperinsulinemic hypoglycemia, familial, 4: Proposed mechanisms include impairment of parathyroid hormone by pro-inflammatory cytokines, catecholamine excess in ICU patients, end organ resistance to parathyroid hormone, inhibition of parathyroid hormone secretion and cellular redistribution of iCa.[24], [25] A recent study conducted by Nair P and colleagues [26] showed that vitamin D insufficiency or deficiency were prevalent among ICU patients (78%) and the level did not recover during treatment.