Suitability of recommended limits for fasting glucose tests in women with polycystic ovary syndrome.(RESEARCH)(Clinical report)

Abstract

Background: The Canadian and American Diabetes Associations recommend the use of an oral glucose tolerance test to screen for abnormal glucose tolerance among women with polycystic ovary syndrome when their fasting plasma glucose level is 5.7 mmol/L or more (Canadian guideline) and 5.6 mmol/L or more (American). Our objective was to determine the predictive value of 5.6 mmol/L as a fasting plasma glucose cutoff for detecting abnormal glucose tolerance in women with polycystic ovary syndrome, and then to define the optimal cutoff for this population.

Methods: An oral glucose tolerance test was administered to 105 consecutive women with polycystic ovary syndrome referred to an academic reproductive endocrine clinic. We calculated sensitivity, specificity and likelihood ratios.

Results: The sensitivity of a 5.6 mmol/L cutoff was 48% (95% confidence interval [CI] 30%-67%); its specificity, 98.7% (95% CI 96.1%-100%). With this cutoff, 52% of women with polycystic ovary syndrome whose glucose tolerance is abnormal would be missed. The prevalence of abnormal glucose tolerance was 28%, with a positive predictive value of 93% (95% CI 81%-100%) and a negative predictive value of 83% (95% CI 76%-91%). The likelihood ratio for a positive test was 36.7 (95% CI 5.0-267), and for a negative test, 0.5 (95% CI 0.4-0.7). The optimal fasting plasma glucose cutoff value was 5.0 mmol/L, with a 79% sensitivity (95% CI 65%-94%) and 66% specificity (95% CI 55%-77%). If this cutoff were used, 24% of women with abnormal glucose tolerance would still be missed.

Interpretation: The Canadian and American recommendations--of screening for abnormal glucose tolerance with an oral glucose tolerance test only when the results of a fasting plasma glucose test are 5.7 mmol/L (or 5.6 mmol/L) or more--are inappropriate for women with polycystic ovary syndrome. We therefore recommend that all women with polycystic ovary syndrome have an oral glucose tolerance test.

CMAJ 2007;176(7):933-8

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Polycystic ovary syndrome is a common disorder affecting some 6%-10% of women of reproductive age. (1-3) Although it is the clinical manifestations of chronic anovulation and hyperandrogenemia that usually bring these women to visit a physician, insulin resistance and hyperinsulinemia are also frequent in this population (4-10) and play an important etiologic role. (11-17) Indeed, the prevalence rates of impaired glucose tolerance and type 2 diabetes in women with this syndrome are both higher than expected for women of similar age, reaching 30%-40% and 10%, respectively. (18,19) Moreover, hypertension, an atherogenic lipid profile and obesity are more prevalent in this population than among age-matched control subjects. (20,21) This adverse metabolic profile contributes to an excess cardiovascular risk in this youthful population. (22,23)

Since abnormal glucose tolerance is a major cardiovascular risk factor, it is important that it be detected early. The progression to type 2 diabetes can be prevented by lifestyle changes in people whose glucose tolerance is impaired. (24,25)

Despite some evidence that fasting plasma glucose testing does not reliably predict abnormal glucose tolerance in women with polycystic ovary syndrome, (18,26) current Canadian and American guidelines still rely mainly upon this test for screening. Notably, guidelines from the Canadian Diabetes Association (27) recommend an oral glucose tolerance test for people at risk (including women with polycystic ovary syndrome) only when their fasting plasma glucose result reaches 5.7 mmol/L or more. The American Diabetes Association suggests that screening for abnormal glucose tolerance be considered for young patients if they are overweight and present another risk factor for diabetes, such as polycystic ovary syndrome (level of evidence E). (28) Furthermore, the US association does not recommend an oral glucose tolerance test over a fasting plasma test for screening (level B) unless the results of a fasting plasma glucose test are 5.6 mmol/L or more (level E). Because the fasting tests are, in most clinical settings, easier to perform as well as less expensive, most clinicians applying these recommendations will therefore not conduct oral glucose tolerance tests when their patient's fasting plasma glucose measurement meets or exceeds 5.7 (or 5.6) mmol/L.

Since fasting plasma glucose results have been shown to be not well correlated with abnormal glucose tolerance in women with polycystic ovary syndrome, we hypothesized that these recommendations may be inappropriate for patients with that syndrome. The aim of this study was therefore to determine the predictive value of a fasting plasma glucose cutoff of 5.6 mmol/L to identify people with abnormal glucose tolerance among those with polycystic ovary syndrome, and to define the optimal cutoff for the fasting test for this subpopulation. We performed our analyses with the American Diabetes Association's more conservative fasting plasma glucose cutoff because, if our hypothesis was true, our conclusion would also apply to the Canadian Diabetes Association's slightly higher recommendation ([greater than or equal to] 5.7 mmol/L).

Methods

This retrospective study looked at test results for 168 consecutive women with polycystic ovary syndrome referred to the Reproductive Endocrine Clinic of the Centre hospitalier universitaire de Sherbrooke from August 2003 through December 2005. All women met the…