Insulin levels in normal fasting dogs are less than 29 μU/mL. (note new reference range) To investigate hypoglycaemia, samples for insulin assay should be taken during a period when the blood sugar is known to be low. If the insulin levels are greater than 29 μU/mL this is considered to be excessive secretion. Guidelines for the interpretation of fasting insulin are given below.

Insulin greater than 29 μU/mL
Insulin 16 – 29 μU/mL
Insulin 8.3 – 16 0μU/mL
Insulin less than 8.3 μU/mL

High insulin, insulinoma very likely
High/normal insulin, insulinoma likely
Low/normal insulin, insulinoma possible if glucose very low
Undetectable/low insulin – insulinoma very unlikely

Repeat estimation of borderline results may be required to confirm the diagnosis of insulinoma. Elevated insulin in combination with normal or elevated glucose is consistent with insulin resistance rather than insulinoma.

Insulin/Glucose Ratio (IGR)

The IGR is useful when absolute hyperinsulinaemia (insulin >29 μU/mL) is not present and the insulin levels alone are not diagnostic. Glucose and insulin are measured on the same sample.

IGR of >7.0 U/mol (note new reference range) is consistent with insulinoma when glucose is low or low-normal. An elevated ratio in an animal with high normal or high glucose indicates insulin insensitivity.

Amended Insulin/Glucose Ratio (AIGR)

The AIGR is reported to be more helpful in some cases and is calculated on the assumption that insulin levels should be undetectable if the blood glucose falls below 30 mg/dL (1.7 mmol/L).

Note: If glucose is <30mg/dL then the divisor becomes 1.0. Interpretation
AIGR of >50 is consistent with insulinoma when blood glucose is subnormal.

Equine Insulin

Horses with PIA and “peripheral hyperadrenocorticism” often have very high serum insulin levels due to peripheral insulin resistance.