Bipolar unspecified (BP-U) is an important cause of morbidity and mortality in hospitalized patients. While BP-U has been extensively studied in the past, the contemporary data for impact of BP-U on cost of hospitalization are largely lacking.

We queried the Healthcare Cost and Utilization Project's Nationwide Inpatient Sample (HCUP-NIS) dataset between 1998–2011 using the ICD-9 codes. Severity of comorbid conditions was defined by Deyo modification of Charlson comorbidity index. Primary outcome was in-hospital mortality and secondary outcome was total charges for hospitalization. Using SAS 9.2, Chi2 test, t-test and Cochran-Armitage test were used to test significance.

A total of 711,147 patients were analyzed; 61.33% were female and 38.67% were male (P < 0.0001); 77.63% were white, 13.17% black and 9.2% of other race (P < 0.0001). Rate of hospitalization increased from 2,310.28/million to 74,908.88/million from 1998–2011. Overall mortality was 0.81% and mean cost of hospitalization was $25,152.02. The in-hospital mortality reduced from 1.24% to 0.97% (P < 0.0001) and mean cost of hospitalization increased from 11,308.05$ to 32,211.67$. Total yearly spending on BP-U related admissions have increased from $207 million/year to $19.15 billion/year.

While mortality has slightly decreased from 1998 to 2011, the cost has significantly increased from $0.21 billion/year $19.15 billion/year, which leads to an estimated $18.94 billion/year additional burden to US health care system. In the era of cost conscious care, preventing BP-U related hospitalization could save billions of dollars every year. Focused efforts are needed to establish preventive measures for BP-U related hospitalization.

The authors have not supplied their declaration of competing interest.