Bipolar II (B-II) is an important cause of morbidity and mortality in hospitalized patients. While B-II has been extensively studied in the past, the contemporary data for impact of B-II 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 107,152 patients were analyzed; 62.61% were female and 31.39% were male (P < 0.0001); 78.19% were white, 11.44% black and 10.37% of other race (P < 0.0001). Rate of hospitalization increased from 866.87/million to 8156.03/million from 1998–2011. Overall mortality was 0.32% and mean cost of hospitalization was 19,447.89$. The in-hospital mortality increased from 0.00% to 0.07% (P < 0.0001) and mean cost of hospitalization increased from 7565.20$ to 26,511.95$. Total yearly spending on B-II related admissions have increased from $52.24 million/year to $1.6 billion/year.

While mortality has slightly increased from 1998 to 2011, the cost has significantly increased from $52.24 million/year to $1.6 billion/year, which leads to an estimated $1.55 billion/year additional burden to US health care system. In the era of cost conscious care, preventing B-II related hospitalization could save billions of dollars every year. Focused efforts are needed to establish preventive measures for B-II related hospitalization.

The authors have not supplied their declaration of competing interest.