Does gender bias exist in the use of specialist health care?

To investigate the evidence for the existence of gender bias (defined as care provided independently of clinical need) in the use of specialist services by critically appraising the literature. A computer-assisted search of the bibliographic databases PubMed, Medline, EMBASE, Healthstar and Social Science Citation Index for English language papers published from 1966 until May 1999. In addition, four journals were handsearched and the reference lists of identified papers were explored. Retrospective studies were only used when there were insufficient prospective studies. One hundred and thirty-eight studies were identified covering five major topics: coronary artery disease; renal transplantation; human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS); mental illness; and other (mainly invasive) procedures. The majority (94) examined coronary artery disease. It appears that men are more likely to undergo non-invasive investigations than women, but that subsequent investigation and treatment shows no clear evidence of gender differences. Men are more likely to undergo renal transplantation and, for those with HIV and AIDS, to receive azidothymidine (zidovudine, AZT) than women. There are some indications that disparities in favour of men also occur for those suffering from cardiac arrhythmias and cerebrovascular disease, and for those undergoing vascular surgery, hip replacement and heart transplantation. In contrast, women are more likely to undergo liver transplantation and cataract surgery. Mental health services may be provided differently for men and women. All these findings are limited by a lack of accurate denominator information and insufficient ability to adjust for prognostic factors. Differences in health care use can be due to demand factors (e.g. differences in the prevalence and severity of disease or in patient preferences), supply factors (particularly clinical judgement), or both. There is a need to examine these explanations thoroughly for gender inequalities in order to ensure that equity (lack of bias) is achieved. There is also a need for higher quality studies if differences are to be attributed conclusively to bias or not