title: Comparison of surrogate and direct measurement of insulin resistance in chronic hepatitis C virus infection: impact of obesity and ethnicity.
abstract: Studies using surrogate estimates show high prevalence of insulin resistance in hepatitis C infection. This study prospectively evaluated the correlation between surrogate and directly measured estimates of insulin resistance and the impact of obesity and ethnicity on this relationship. Eighty-six nondiabetic, noncirrhotic patients with hepatitis C virus (age = 48 +/- 7 years, 74% male, 44% white, 22% African American, 26% Latino, 70% genotype 1) were categorized into normal-weight (body mass index [BMI] < 25, n = 30), overweight (BMI = 25-29.9, n = 38), and obese (BMI > or = 30, n = 18). Insulin-mediated glucose uptake was measured by steady-state plasma glucose (SSPG) concentration during a 240-minute insulin suppression test. Surrogate estimates included: fasting glucose and insulin, glucose/insulin, homeostasis model assessment (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), insulin (I-AUC) and glucose (G-AUC) area under the curve during oral glucose tolerance test, and the Belfiore and Stumvoll indexes. All surrogate estimates correlated with SSPG, but the magnitude of correlation varied (r = 0.30-0.64). The correlation coefficients were highest in the obese. I-AUC had the highest correlation among all ethnic and weight groups (r = 0.57-0.77). HOMA-IR accounted for only 15% of variability in SSPG in the normal weight group. The common HOMA-IR cutoff of < or =3 to define insulin resistance had high misclassification rates especially in the overweight group independent of ethnicity. HOMA-IR > 4 had the lowest misclassification rate (75% sensitivity, 88% specificity). Repeat HOMA-IR measurements had higher within-person variation in the obese (standard deviation = 0.77 higher than normal-weight, 95% confidence interval = 0.25-1.30, P = 0.005).
  
  
  CONCLUSIONS
  Because of limitations of surrogate estimates, caution should be used in interpreting data evaluating insulin resistance especially in nonobese, nondiabetic patients with HCV.
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, CA, USA.
authors.forename: Khoa D
authors.initials: KD
authors.lastname: Lam
authors.forename: Peter
authors.initials: P
authors.lastname: Bacchetti
authors.forename: Fahim
authors.initials: F
authors.lastname: Abbasi
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Ayala
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Loeb
authors.forename: Vidhi
authors.initials: V
authors.lastname: Shah
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wen
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Reaven
authors.forename: Jacquelyn J
authors.initials: JJ
authors.lastname: Maher
authors.forename: Mandana
authors.initials: M
authors.lastname: Khalili
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose; D002140:California / Q000453:epidemiology; D005260:Female; D019698:Hepatitis C, Chronic / Q000453:epidemiology* / Q000208:ethnology*; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000208:ethnology*; D015995:Prevalence; D055815:Young Adult
chemical_list: D001786:Blood Glucose