Pointers to earlier diagnosis of endometriosis: a nested case-control study using primary care electronic health records

Background Endometriosis is a condition with relatively non-specific symptoms and in some cases a long time from first symptom presentation to diagnosis. Aim We aimed to develop and test new composite pointers to a diagnosis of endometriosis in primary care electronic records. Design & Setting Nested case-control study using the Practice Team Information database of anonymised primary care electronic health records from Scotland. Data from 366 cases of endometriosis between 1994 and 2010 and two sets of age and GP practice matched controls (a) 1453 randomly selected women (b) 610 women whose records contained codes indicating consultation for gynaecological symptoms. Methods Composite pointers comprised patterns of symptoms, prescribing or investigations, in combination or over time. We used conditional logistic regression to examine the presence of both new and established pointers during the three years before diagnosis of endometriosis and identify when they appeared. Results Several composite pointers were strongly predictive of endometriosis: including pain and menstrual symptoms occurring within the same year (OR 6.5, 95% CI 3.9 to 10.6) and lower gastrointestinal symptoms occurring within 90 days of gynaecological pain (OR 6.1, 95% CI 3.6 to 10.6). While the association of infertility with endometriosis was only detectable in the year before diagnosis, several pain-related features were associated with endometriosis several years earlier. Conclusions We have identified useful composite pointers to a diagnosis of endometriosis in GP records. Some of these were present several years before the diagnosis and may be valuable targets for diagnostic support systems.