Practical methodological strategies for individual patient data systematic reviews

Diabetes-related leg amputations are associated with substantial morbidity and mortality and are usually preceded by foot ulceration. Annual assessment procedures are recommended to identify people with diabetes who are at risk of foot ulceration. Some evidence suggests the use of specific diagnostic tests, symptoms, signs, and elements from the patients' history, but the role of other contributory factors is unclear. Clinical guidelines for foot screening are largely based on consensus and on the findings from individual studies rather than on any systematic integration of all available data. Systematic reviews to integrate evidence of predictive factors exist, but are compromised because both adjusted and unadjusted estimates are present in the primary studies. Because adjusted meta-analyses of aggregate data can be challenging, the best way to standardise the analytical approach is to use individual patient data (IPD). There are many challenges associated with this type of systematic review including its time-consuming and costly nature. We will share the key methodological strategies that underpin our IPD systematic review of prognostic factors for foot ulceration in diabetes. We have three aims: (1) to systematically review individual patient data from cohort studies in a meta-analysis to estimate the predictive value of clinical characteristics and diagnostic tests for diabetic foot ulceration; (2) to develop a prognostic model of the risk factors for diabetic foot ulceration on the basis of data obtained worldwide; and (3) to test the robustness of the model in different demographic profiles (eg, age, duration of diabetes, control of diabetes [insulin, diet, or oral medication], and type of diabetes [type I or II]).