How is insulin sensitivity assessed in the workup of insulin resistance?

Updated: Aug 07, 2019
  • Author: Samuel T Olatunbosun, MD, FACP, FACE; Chief Editor: George T Griffing, MD  more...
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Answer

In theory, insulin sensitivity can be assessed through the following methods:

  • Fasting insulin level - This provides an indirect assessment of insulin sensitivity. The limitation of this study is inaccuracy in a patient with mutant insulin in which the hormone measured by radioimmunoassay is not fully bioactive.

  • Measurement of response to direct intravenous infusion of insulin - The limitations of this measurement are a confounding factor in data interpretation and a variation in secretion of antagonist hormones in response to hypoglycemia.

  • Euglycemic insulin clamp technique - Plasma glucose levels are held constant, with variable glucose infusion. Biochemical responses that are surrogate estimates of insulin resistance, such as glucose disposal and antilipolysis, are determined. This method is considered the criterion standard.

  • The latter two tests are more accurate, but they are research tools and are not routinely used in clinical practice.

  • Homeostatic model assessment for insulin resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI) - These are the most widely used simple indices for assessing insulin resistance in clinical research and practice. Both indices are based on fasting glucose and insulin measurements; they differ mainly in the log transformation of these variables in QUICKI. [53, 54, 55]

  • HOMA-IR is derived from the product of the insulin and glucose values divided by a constant--that is, calculated by using the following formula: fasting glucose (mg/dL) X fasting insulin (µU/mL) / 405 (for SI units: fasting glucose (mmol/L) X fasting insulin (µU/L) / 22.5). A value greater than 2 indicates insulin resistance.

  • QUICKI is derived by calculating the inverse of the sum of the logarithmically expressed values of fasting insulin and glucose: 1/[log(fasting glucose) + log(fasting insulin)] . It measures insulin sensitivity, which is the inverse of insulin resistance. A value of less than 0.339 indicates insulin resistance.

  • They both compensate for fasting hyperglycemia, and the results for the indices correlate reasonably well with the euglycemic clamp technique. Some investigators believe that QUICKI is superior to HOMA-IR (for instance, in reproducibility), but the two indices correlate very well. [56, 57, 58]

  • One study suggests fasting insulin sensitivities are not better than routine clinical variables in predicting insulin sensitivity in black Africans. [59]


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