Unexplained transient hyperphosphatemia is more common in acute psychiatric disorders than in acute medical-surgical conditions

Increased serum inorganic phosphorus associated with elevated serum calcium has been demonstrated to coincide with the onset of agitation and mania in periodic psychoses and bipolar disorders. We tested the hypothesis that unexplained transient hyperphosphatemia (UTHP) is more common in patients with psychiatric disorders than in controls with medical or surgical conditions. We studied 100 patients admitted to a psychiatric ward and 100 controls admitted to a medical-surgical ward. All subjects (patients and controls) underwent acute admission to the same general hospital. The serum phosphorus was measured upon admission and, if elevated, followed during the hospital course. Twenty patients (20%) with psychiatric disorders had unexplained hyperphosphatemia compared with four medical-surgical controls (4%). UTHP occurred in six patients with psychiatric disorders and no controls. Hypophosphatemia did not occur in subjects with psychiatric disorders. This study shows an increased incidence of UTHP in acutely ill, hospitalized patients with psychiatric disorders relative to acutely ill, hospitalized controls with medical-surgical conditions. These data extend previous findings by linking UTHP to acute psychiatric disturbances across varied psychiatric diagnoses independent of hypercalcemia. Potential explanations include trazodone administration and transient hypocalcemia.