Belfiore F, Iannello S, Camuto M, Fagone S, Cavaleri A
Institute of "Medicina Interna e Specialità Internistiche," Chair of Internal Medicine, University of Catania Medical School, Catania, Italy.
Metabolism. 2001 May;50(5):573-82. doi: 10.1053/meta.2001.22518.
We calculated insulin sensitivity indices (ISI) concerning the insulin effect on both glycemia and blood free fatty acids (FFA), named ISI(gly) and ISI(ffa), respectively, in 34 normal, 27 obese, and 11 obese-diabetic subjects by using the following formulas: ISI(gly)= 2/[(INSp x GLYp) +1], and ISI(ffa)= 2/[(INSp x FFAp)+1], in which INSp, GLYp, and FFAp = insulinemic, glycemic, and FFA areas during oral glucose tolerance test (OGTT) (75 g glucose, suggested sampling time: 0, 1, and 2 hours) of the person studied. A slight modification of these formulas allows the calculation of insulin resistance indices (IRI), ie, IRI(gly) and IRI(ffa). ISI and IRI are complementary, as their sum is always equal to 2, so that IRI can be deduced from ISI and vice versa. By using basal levels instead of areas, insulin sensitivity (or resistance) in the basal state can also be measured. Basal levels and areas are expressed by taking the mean normal value as 1, so that in normal subjects ISI(gly) and ISI(ffa), as well as IRI(gly) and IRI(ffa), are always around 1, with maximal variations comprised between 0 and 2. ISI(ffa) was markedly reduced in both the obese (mean, 0.47 +/- 0.04) and the obese-diabetic (mean, 0.41 +/- 0.06) subjects, whereas ISI(gly) was less reduced in the obese (mean, 0.57 +/- 0.04) than in the obese-diabetic (mean, 0.40 +/- 0.03) subjects. ISI(gly)-basal was less affected than ISI(ffa)-basal in both groups. Multiple regression showed that ISI(gly) and ISI(ffa) were significantly inversely correlated with age, body mass index (BMI), and diastolic (but not systolic) blood pressure. Meta-analysis of data from the literature showed that ISI(gly) was significantly correlated with the hyperinsulinemic-euglycemic clamp data. However, the "clamp" is performed under artificial, persistent hyperinsulinemia (which entails FFA suppression) as never occurs in the life of patients, whereas our indices are performed under physiologic conditions, and represent simple tools suitable for clinical or epidemiologic studies, allowing assessment of whole-body insulin sensitivity with regard to both glycemia and blood FFA.
我们通过以下公式，分别计算了34名正常受试者、27名肥胖受试者和11名肥胖糖尿病受试者中与胰岛素对血糖及血游离脂肪酸（FFA）作用相关的胰岛素敏感性指数（ISI），分别命名为ISI（gly）和ISI（ffa）：ISI（gly）=2/[（胰岛素水平×血糖水平）+1]，ISI（ffa）=2/[（胰岛素水平×FFA水平）+1]，其中胰岛素水平、血糖水平和FFA水平分别为所研究对象口服葡萄糖耐量试验（OGTT，75g葡萄糖，建议采样时间：0、1和2小时）期间的胰岛素血症、血糖血症和FFA面积。对这些公式稍作修改即可计算胰岛素抵抗指数（IRI），即IRI（gly）和IRI（ffa）。ISI和IRI是互补的，因为它们的总和始终等于2，所以IRI可由ISI推导得出，反之亦然。通过使用基础水平而非面积，也可测量基础状态下的胰岛素敏感性（或抵抗）。基础水平和面积以正常平均值为1来表示，因此在正常受试者中，ISI（gly）和ISI（ffa）以及IRI（gly）和IRI（ffa）通常在1左右，最大变化范围在0至2之间。肥胖受试者（平均值为0.47±0.04）和肥胖糖尿病受试者（平均值为0.41±0.06）的ISI（ffa）均显著降低，而肥胖受试者（平均值为0.57±0.04）的ISI（gly）降低程度低于肥胖糖尿病受试者（平均值为0.40±0.03）。两组中，基础状态下的ISI（gly）受影响程度均小于ISI（ffa）。多元回归分析显示，ISI（gly）和ISI（ffa）与年龄、体重指数（BMI）及舒张压（而非收缩压）呈显著负相关。对文献数据的荟萃分析表明，ISI（gly）与高胰岛素正常血糖钳夹试验数据显著相关。然而，“钳夹”是在人工持续高胰岛素血症（这会导致FFA受抑制）条件下进行的，而这在患者实际生活中从未发生过，而我们的指数是在生理条件下进行的，是适用于临床或流行病学研究的简单工具，能够评估全身对血糖及血FFA的胰岛素敏感性。
