How common is bipolar disorder in general primary care attendees? A systematic review and meta-analysis investigating prevalence determined according to structured clinical assessments

There are mounting calls for bipolar disorder to be managed in primary care, yet the exact prevalence remains unclear. We conducted a meta-analysis to investigate the prevalence of bipolar disorder in general primary care attendees without other comorbid psychiatric diagnosis. We systematically searched major electronic databases from inception till 03/2015. Articles were included that reported the prevalence of bipolar disorder determined in line with structured clinical assessment in primary care settings. Two independent authors conducted searches, completed methodological appraisal and extracted data. A random effects meta-analysis and meta-regression were performed. Sixteen studies were included accounting for 425,691 participants (mean age = 41.1 years [standard deviation = 7.2 years] 33.3% males). Overall, the global prevalence of bipolar disorder was 1.9% (95% confidence interval = [0.6, 5.4]). The prevalence of bipolar disorder in studies recording a current diagnosis was 3.7% (95% confidence interval = [1.9, 6.0]) and 0.7% (95% confidence interval = [0.2, 1.5]) in studies considering a 12-month period. A diagnosis of bipolar disorder appeared higher in North America (3.7%, 95% confidence interval = [0.9, 8.1]) compared to Europe (0.8%, 95% confidence interval = [0.3, 1.5]). Meta-regression suggests that a more recent publication date (co-efficient = 0.089, 95% confidence interval = [0.0173, 0.1654], z = 2.19, p = 0.01, R(2) = 0.21) and younger age of participants (co-efficient -0.0851, 95% confidence interval = [-0.1696, 0.005], z = -1.97, p = 0.04, R(2) = 0.24) moderated a higher prevalence of bipolar disorder. The global prevalence of bipolar disorder in primary care is 1.9%, with potentially higher prevalence rates in North America compared to Europe. A more recent study publication date is a significant predictor of higher prevalence of bipolar disorder. Potential reasons/drivers of this are considered within the text.