insulin-to-glucose ratio =
= ((insulin) / (glucose - 30)) * 100
where:
• 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).
Interpretation:
• 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
Method:
(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.
Interpretation:
• 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.
