Endocrine Abstracts

Backgroud: Though insulin resistance (IR) is common in polycystic ovary syndrome (PCOS), there is no agreement as to what surrogate method of assessment of IR is most reliable.

Aim: We compared methods based on measurements of fasting insulin and either fasting glucose (HOMA-IR and QUICKI), or triglycerides (TAG) (McAuley index) with insulin resistance (Belfiore) index (IRI) derived from glucose and insulin during a 75-g oral glucose tolerance test (OGTT).

Subjects and methods: Glucose (G) and insulin (I) were measured during OGTT in 478 patients with PCOS (Rotterdam criteria). IR indices were calculated according to the formulae: HOMA-IR=[G] (mmol/l) × [I] (μU/ml)/22.5, QUICKI =1/[log(I) + log(G)]; while IRI =2/[(INSp x GLYp) +1], where INSp, GLYp = insulinaemic and glycaemic areas during OGTT. McAuley index was calculated as Mffm/I=e [2.63–0.28 ln (I) – 031 ln (TAG)].

Results: There was a significant (P<0.001), but modest correlation between IRI and HOMA (R=0.582), IRI and QUICKI (r=−0.580), and IRI and McAuley index (r=−0.614). In contrast, there was an excellent correlation between HOMA-IR and QUICKI (r=−0.999, P<0.001), and HOMA & McAuley index (r=−0.849, P<0.01). Concordance between HOMA-IR and IRI was poor for subjects with HOMA-IR or IRI above 75^th and 90^th percentile i.e. those most insulin resistant. In particular, only 53% (70/132) women with HOMA-IR>75^th percentile had IRI value also above 75^th percentile, while only 44% (24/54) of women with HOMA above 90^th percentile, also had IRI value above 90^th percentile. This discrepancy was even more striking for comparison between IRI and McAuley index, where 121/126 (96%), and 52/53 (98%) women with IRI above 75^th, and 90^th percentile had the value of McAuley index below 75^th and 90^th percentiles, respectively.

Conclusions: Significant number of women with PCOS can be classified as being either insulin sensitive, or insulin resistant depending on the method applied, with the greatest discrepancies existing for comparison of between IRI (Belfiore) and McAuley indices. Clinical application of surrogate indices for assessment of IR in PCOS must be therefore viewed with an extreme caution.