[Using nested case-control study to appraise the effectiveness of Chinese medicines in the treatment of diabetic nephropathy].

Objective: A nested case-control study was carried out to assess the effectiveness of Chinese medicines in the treatment of diabetic nephropathy, so as to explore the feasibility of using nested case-control study on effect assessment of Chinese medicine.

Methods: Nested case-control study was applied and the participants were enrolled from the subjects recruited in a cohort study. The cases and the controls were matched by 1 to 4 in age, gender, nationality and the stage of diabetic nephropathy when recruited in the cohort study. The EpiData 3.1 software was used for inputting data and SAS system was used for data analysis. Conditional logistic regress was applied to analyze the relationship between treatment and the progression of diabetic nephropathy. The study power was estimated and the sample sizes for case-control study and cohort study were recalculated based on the data from the cohort study.

Results: Eight cases and 32 controls were recruited in this study. The education level, ratio of drug withdrawal, change of therapy, syndrome differentiation and treatment were not significantly different in case and control groups. The progression of diabetic nephropathy was not significantly related with the treatment and the odds ratio (OR) value was 0.725 with a 95% confidence interval from 0.174 to 3.030. The statistical power of the study was 5%. To achieve the statistical power of 80%, 1 350 (270:1 080) participants were needed for 1:4 matched case-control study, 880 (440:440) for 1:1 paired case-control study, and 1 020 (510:510) for 1:1 control study.

Conclusion: The treatment method is not significantly related with the progress of diabetic nephropathy. The nested case-control study is applicable in the therapeutic effect evaluation of Chinese medicine. Basic studies such as cross-sectional studies should be carried out to supply fundamental information for other types of studies including case-control study, cohort study and randomized clinical trials. Large sample size studies were needed to appraise the effect of Chinese medicine.