Association between prolactin and disease activity in systemic lupus erythematosus.: Influence of statistical power

Objective. To analyze the statistical power of studies in the medical literature on the relationship between prolactin (PRL) and systemic lupus erythematosus (SLE) activity. Methods. Published studies that were identified through MEDLINE search, as well as references from these articles, were reviewed. Results, We identified 5 articles that sought to establish a relationship between PRL and SLE activity. In 4 of them, the frequency of hyperprolactinemia in SLE (> 20 ng/ml) was 2.2-47.2%, and in one article, there was a relationship between PRL and SLE activity. A power analysis of individual studies could be carried out in only 2 of the 5; there were no significant effects; the 2 articles cited differences in the frequency of hyperprolactinemia in patients with and without lupus activity (1.6 and 12.3%, respectively), but because of a low power of the studies (greater than or equal to 30.8%), it could not be determined whether the differences in the frequency of hyperprolactinemia were significant. On the other hand, joint analysis of 3 articles showed a significant association between hyperprolactinemia and lupus activity. Conclusion. Published clinical results concerning the relationship between PRL and lupus activity an contradictory, due in part to the statistical power of the studies. Our analysis of these studies showed that PRL is related to lupus activity, without establishing a formal causal relationship.