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Insulin and Insulin/Glucose Ratio



DEFINITION


Insulin is a hormone produced and secreted by the β cells of the pancreatic islets of Langerhans. It promotes cellular uptake of glucose, notably by fat, skeletal muscle, and liver, but not neurons, red blood cells (RBCs), renal tubular epithelial cells, enterocytes, or ocular lens. It promotes anabolic metabolism of carbohydrates, proteins, lipids, and nucleic acids.


The amended insulin/glucose ratio is calculated according to the following formula: serum insulin (μU/mL) × 100/ serum glucose (mg/dL) − 30; if the denominator is negative, substitute 1.


This formula compares the insulin concentration in relationship with serum glucose concentration; however, it is generally considered inaccurate and should not be used. Rather, the absolute serum insulin concentration during hypoglycemic episodes should be evaluated along with history, physical examination findings, and laboratory test results.



TYPICAL NORMAL RANGE


Serum insulin reference interval varies with laboratory and should be established for each laboratory. Insulin/glucose ratio <30 is considered normal, ratio >30 is suggestive of hyperinsulinism but is nonspecific for neoplasia (other causes of hypoglycemia also elevate this ratio in dogs).



PHYSIOLOGY


Under normal conditions, high blood glucose levels trigger insulin release, and high insulin levels decrease blood glucose levels. This feedback mechanism ensures glucose homeostasis and is the reason the insulin/glucose ratio is low (<30) in health. Persistent and/or excessive (e.g., paraneoplastic) hyperinsulinism may cause rapid, excessive cellular uptake of glucose, which results in hypoglycemia and associated clinical signs. Decreased concentrations of insulin are absolute with type I diabetes mellitus and often relative with type II and type III diabetes mellitus.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Pancreatic β-cell neoplasia (insulinoma), leiomyosarcoma, insulin therapy, artifact (see below)


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Measure serum glucose concentration simultaneously. Assess pancreas and small intestine by ultrasonographic examination.


CAUSES OF ABNORMALLY LOW LEVELS: Diabetes mellitus, although serum insulin levels are not usually measured as part of diagnosis or management of diabetic patients


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: Check serum glucose concentration, urine glucose, and urine ketones. In diabetes mellitus, the serum glucose is increased; if untreated, there is often glucosuria ± ketonuria.



SPECIMEN AND PROCESSING CONSIDERATIONS


LAB ARTIFACTS THAT MAY INTERFERE: Antiinsulin antibodies (contributors to diabetes mellitus) interfere with insulin assays and cause false, markedly increased insulin concentration results.


SPECIMEN: Serum (red-top tube)


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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on I

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