The insulin-glucose ratio corrects for technical problems in the insulin assay. Because insulin secretion in healthy beta-cells is reduced to basal levels with hypoglycemia, insulin would not be detectable at glucose levels of about 30 mg/dL. It is used in the diagnosis of insulinoma, where secretion of insulin is independent of glucose levels. The change in the ratio during more prolonged fasting gives a better diagnostic separation between patients with inappropriate islet cell secretion from normal subjects.


insulin-to-glucose ratio =

= ((insulin) / (glucose - 30)) * 100



• Insulin is given in microunits/mL

• Glucose is given in mg/dL.

• The ratio is expressed in microunits/mg (the "100" corrects for the mL and dL).



• normal: up to 100 microunits/mg (another study used 50 as the upper limit)

• insulinoma: 180 microunits/mg, although some patients may have normal ratios


Insulin-to-Glucose Ratio After Overnight or Prolonged Fasting



(1) If pancreatic islet cell is strongly suspected, the patient is observed as an inpatient while fasting. If the suspicion is not strong, the patient can be tested as an outpatient.

(2) The patient is instructed to have an evening meal at 17:00-18:00 but to fast thereafter.

(3) Starting at 08:00 the next morning, serum is collected for insulin and glucose levels every 1-2 hours through mid-afternoon, and then the insulin-to-glucose ratio is calculated.

(4) If severe hypoglycemia develops then the test is terminated.



• If a patient shows normal insulin to glucose ratios while fasting for 18-22 hours, then the diagnosis of pancreatic islet cell disease with hyperinsulinemia is ruled out for practical purposes.


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