Comment to: Martin S, Schneider B, Heinemann L et al (2006) Self-monitoring of blood glucose in type 2 diabetes and long-term outcome: an epidemiological cohort study. Diabetologia 49:271–278

Abstract

If causally interpreted, self-monitoring of blood glucose (SMBG) in type 2 diabetes reduces mortality by about 50% [1]. The benefit emerges swiftly, as suggested by the Kaplan–Meier survival curves. We wonder whether pricking fingers might be the most effective intervention ever reported in type 2 diabetes. Unfortunately, the study in question is an example of observational research fallacies. The study lacks internal validity. The design is uncontrolled. Patients were not examined personally. Instead, routine medical records of a self-selected group of primary care physicians without experience in performing clinical research were used to extract patient data for analysis. Important bias and confounders are likely. Differences in the nature and severity of diabetes have not been ruled out. Heterogeneity among groups is likely. Assessments of variables such as blood pressure measurements have not been standardised. In particular, social class and indicators of social support were not documented. Socioeconomic status is a most important prognostic factor for morbidity and mortality in diabetes [2, 3]. This is of particular importance for the present analysis, since for most patients with type 2 diabetes in Germany SMBG is not reimbursed. Therefore, the study could be seen as measuring the hidden effect of social class and social capital among individuals with type 2 diabetes rather than the effect of SMBG. Even the few characteristics available from the medical records indicate some important differences between patients using SMBG and those who do not. The SMBG group is younger and has lower systolic blood pressure. Other unknown differences are conceivable. The huge number of missing