Does additional confounder information alter the estimated risk of bleeding associated with phenprocoumon use--results of a two-phase study.

摘要

Claims databases are an important source for pharmacoepidemiological studies although they often lack information on some confounders. Two-phase methodology was used to estimate the bleeding risk in patients treated with phenprocoumon from claims data combined with additional information on body mass index (BMI) and smoking.We conducted a nested case-control study using claims data from 2004 to 2007 (phase 1). Additional information was obtained from interviews in a subset of 505 insurants (phase 2). Adjusted bleeding OR were calculated using logistic regression using data from the complete case-control dataset. Furthermore, a two-phase analysis was conducted, taking into consideration phase 2 data on BMI and smoking.The phase 1 sample included 1248 cases and 24,960 controls. In phase 1, we observed an adjusted bleeding ORs of 3.93 (95%CI: 2.75-5.61) for male subjects aged 55 years taking phenprocoumon. The bleeding risk associated with phenprocoumon use decreased with increasing age. The two-phase analysis revealed smoking and a high BMI as risk factors for bleeding. The OR for phenprocoumon obtained from the two-phase analysis was of similar size as the phase 1 estimate.Phase 2 data added valuable information on smoking and BMI. However, phase 1 results did not change dramatically after accounting for phase 2 information, which is reassuring for the validity of database studies.