Comparison of short insulin tolerance test with HOMA

Comparison of short insulin tolerance test with HOMA

diabetes research and clinical practice 82 (2008) e9–e12 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/diabres Brief...

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diabetes research and clinical practice 82 (2008) e9–e12

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/diabres

Brief report

Comparison of short insulin tolerance test with HOMA Method for assessment of insulin sensitivity in Asian Indians in north India Rajeev Sharma a, Naval K. Vikram a, Anoop Misra a,b,* a b

Department of Internal Medicine, All India Institute of Medical Sciences, New Delhi 110029, India Department of Diabetes and Metabolic Diseases, Fortis Flt. Lt. Rajan Dhall Hospital, Vasant Kunj, New Delhi 110070, India

article info

abstract

Article history:

Background: Cost-effective method to assess insulin resistance is needed for Asian Indians.

Received 20 June 2008

Methods: We compared HOMA with SITT methods in 40 subjects.

Received in revised form

Results: Values obtained from both methods did not show any correlation.

20 June 2008

Conclusions: Both methods should be evaluated against hyperinsulinemic clamp to deter-

Accepted 1 July 2008

mine suitability in Asian Indians.

Published on line 15 August 2008

# 2008 Elsevier Ireland Ltd. All rights reserved.

Keywords: Asian Indians Metabolic syndrome Insulin resistance

1.

Introduction

Asians Indians have an abnormally high tendency to develop type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD) [1]. Insulin resistance (IR) is an important determinant of both these diseases [2,3]. Body composition of Asian Indians is favorable for the development of the metabolic syndrome; they have high percentage of body fat [4,5] and abdominal adiposity including high-subcutaneous and intra-abdominal fat [4,6]. Non-alcoholic fatty liver disease (NAFLD) is now considered to be a key component of the metabolic syndrome [7] and is present in nearly one-fourth of Asian Indians living in India [8,9]. Currently, insulin sensitivity needs to be assessed in experimental and clinical studies. It is desirable to have a

cost-effective field-based method for measurement of insulin sensitivity in developing countries. Various methods used to assess IR are; ‘‘gold standard’’ euglycemic hyperinsulinemic clamp technique [10], frequently sampled intravenous glucose tolerance test (FSIGT), homeostasis model assessment for IR (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), glucose/insulin ratio (G/I ratio) and insulin tolerance test (ITT) [11]. Homeostatic models like HOMA-IR, which require determination of serum insulin and glucose has been used in many studies [12]. SITT is another, less frequently used method of measurement of insulin sensitivity and has been validated against clamp studies [13,14]. In this study, we planned to compare SITT and HOMA-IR for measuring IR in patients with Asian Indians with NAFLD.

* Corresponding author at: Department of Diabetes and Metabolic Diseases, Fortis Flt. Lt. Rajan Dhall Hospital, Vasant Kunj, New Delhi 110070, India. Tel.: +91 11 4277 6222x5030; fax: +91 11 4277 6221. E-mail addresses: [email protected], [email protected] (A. Misra). 0168-8227/$ – see front matter # 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.diabres.2008.07.010

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2.

Methods

2.1.

Subjects

Forty male subjects were enrolled (from June 2004 to April 2006) after informed consent and institution’s ethical committee approval. Inclusion criteria were: age >18 years, normoglycemia, alcohol intake less than 20 g/day, ultrasound documented hyperechoic liver and negative tests for viral and other known liver diseases. This test sample was compared with 20 age-matched healthy controls with normal values of body mass index (BMI), waist circumference, serum aminotransferases, fasting plasma glucose and normal liver ultrasound.

2.2.

Experimental protocol

Anthropometric measurements, fasting blood glucose, serum insulin and lipids were measured as previously described [15,16]. Insulin sensitivity was calculated by the HOMA-IR [17] and ITT [13]. For ITT blood samples were taken for measurement of plasma glucose and fasting serum insulin after an overnight fast. Subsequently rapid acting insulin (Huminsulin R, Eli Lilly, Indianapolis, IN) was given at an intravenous bolus dose of 0.05 U/kg body weight and the blood samples were collected at the time of injection and at 3, 6, 9, 12 and 15 min. The test was terminated by injection of 25 ml 50% dextrose. Rate constant for ITT (KITT) was calculated using formula KITT (%/min) = 0.693/t1/2, where t1/2 was calculated from the slope of the plasma glucose concentration during the period from 3 to 15 min after insulin injection, using the least square analysis. Lower insulin-sensitivity index (KITT) scores mean higher degrees of insulin resistance. HOMA-IR was calculated as the product of fasting serum insulin (mU/L) and fasting plasma glucose (mg/dl) divided by 405. Since there are no accepted cut off values of HOMA to define IR, we used 2.29 as abnormal value in our study [18].

The metabolic syndrome was defined by the presence of three or more modified adult treatment panel III criteria out of five criteria (abnormal waist circumference, high-fasting plasma glucose, high-blood pressure, high-serum TG, and low-serum HDL) [19]. The statistical analysis was conducted by SPSS package for Windows (SPSS, Chicago, IL). Spearman’s correlation was used to explore the relationship between ITT and HOMA-IR.

3.

Results (Table 1)

The mean age of the patients was 35 years (21–54) Twenty patients (50%) had BMI 25 kg/m2. The mean ALT values in patient group were 72 IU/L (range = 19–232 IU/L). Twenty-eight percent of subjects in the study group had the metabolic syndrome according to NCEP, ATP III criteria [19]. In comparison to healthy controls, patients with NAFLD showed more insulin resistance with both the methods. Patients with NAFLD had significantly lower mean KITT value (1.91%/min [range = 0.47–5.47]) than healthy controls (2.48 [0.74–3.62]). Also, they had higher mean HOMA-IR values (2.08 [0.50–12.42]) than the healthy controls (1.47 [0.40–3.52]). There was no correlation between KITT and HOMA-IR values in the NAFLD patients (r = 0.18 and p = 0.2) (Fig. 1).

4.

Discussion

This study shows that SITT does not correlate with HOMA-IR values for determining insulin sensitivity in patients with non-diabetic Asian Indians with NAFLD. These findings are in contrast to those of Duseja et al. [20] who showed fair correlation between these two methods on 22 Asian Indian patients with NAFLD (r = 0.55 and p = 0.03). The ‘gold standard’, euglycemic hyperinsulinemic clamp technique [10], is cumbersome, expensive and requires a great

Table 1 – Demographic, anthropometric and biochemical data Parameters Age (years) Body mass index, BMI (kg/m2) Waist circumference (cm) Waist-hip ratio Body fat (%) AST (IU/L) ALT (IU/L) Fasting blood glucose (mg/dl) The metabolic syndrome (according to ATP III criteria) Fasting serum insulin (mIU/ml) HOMA-IR Kitt Total cholesterol (mg/dl) Serum triglycerides (mg/dl) HDL-C (mg/dl) LDL-C (mg/dl)

NAFLD group (40) 35.6  9.1 25.3  3.1 92.3  10.3 0.97  0.07 28.6  6.4 47.8  24.3 72.8  56.6 94.3  11.1 11 (28%) 11.8  10.1 2.08  2.49 1.9  1.3 198.7  56.8 190.9  84.2 47.1  4.2 113.0  57.4

Control group (20) 34.1  6.8 21.9  2.5 82.0  11.3 0.89  0.07 22.9  6.2 33.2  8.1 33.9  9.7 103.0  41.9 1 (5%) 2.5  0.7 1.47  0.78 88.0  9.5 6.8  3.6 176.7  42.7 138.7  59.7 46.6  3.3

All values are in mean  standard deviation. ALT: alanine aminotransferase, AST: aspartate aminotransferase; HDL-C: high-density lipoprotein-cholesterol; LDL-C: low-density lipoprotein-cholesterol; Kitt: insulin-induced glucose disposal rate calculated from the slope of the regression line of the logarithm of blood glucose against time; HOMA-IR: homeostasis model assessment-insulin resistance; ATP III: National Cholesterol Education Program, Adult Treatment Panel III.

diabetes research and clinical practice 82 (2008) e9–e12

Fig. 1 – Graph showing correlation between rate constant for insulin tolerance test (KITT) (Y-axis) and homeostasis model assessment for insulin resistance (HOMA) (X-axis) in patients with NAFLD (r = S0.18 and p = 0.2).

deal of expertise and is not an ideal method for epidemiological studies. Both HOMA and SITT methods could be useful for developing country like India. HOMA is probably the easiest method to perform although but it involves measurement of serum insulin which may not be available and is expensive in resource-constrained settings in India. SITT is a safe, inexpensive and easy-to-perform test [21]. However, the limitations of SITT are frequent sampling, possibility of hypoglycemia, and confounding due to secretion of counter-regulatory hormones like cortisol and epinephrine in response to insulin-induced hypoglycemia. However, these responses appear 15–20 min after insulin injection [22]. In our study, the test was completed at 15 min thus avoiding the counter-regulatory hormone response interfering with the rate of glucose fall. To conclude, based on this study, it is not possible to choose between two easy methods of measurement of insulin sensitivity, HOMA and SITT for Asian Indians. These methods need evaluation against hyperinsulinemic euglycemic insulin clamp method.

Conflict of interest There are no conflicts of interest.

Acknowledgement None.

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