Elevated blood urea nitrogen and medical outcome of psychiatric inpatients

Elevated blood urea nitrogen (BUN) is associated with increased severity of illness and mortality, but its predictive value has not been studied in patients admitted to free-standing psychiatric hospitals. To determine the clinical outcome of psychiatric inpatients with elevated BUN on admission and to create a quantitative method of using BUN for predicting deteriorations requiring transfers of psychiatric inpatients to a general hospital we conducted a retrospective cohort study of 939 adults consecutively admitted to a free-standing psychiatric hospital in 2010. Transfer to a general hospital was used as a proxy marker for poor medical outcome. The score Age (years) plus BUN (mg/dL) was used in sensitivity analyses to identify patients with medical deterioration in derivation (N = 523) and validation (N = 414) samples. Fifty-two (5.5%) patients had admission azotemia (BUN >25 mg/dL). Medical deteriorations requiring emergency transfer to a general hospital occurred in 24 (46.2%; 95% confidence interval = 32.6-49.8%) of azotemic patients and 112 (12.6%; 95% confidence interval = 10.4-14.8%) of those with normal BUN (p < 0.0001). Age + BUN ≥ 90 identified 51 transferred patients and had positive and negative predictive values of 39.8 and 89.5%, respectively, in the entire sample. We conclude that psychiatric inpatients with BUN >25 mg/dL or Age + BUN ≥ 90 are at risk for medical deterioration. Free-standing psychiatric hospitals should develop models of care requiring frequent, scheduled medical follow-up and enhanced monitoring for this vulnerable populations.