Insulin test explained

Insulin is a hormone produced by the beta cells of the pancreas. Its main function is to help cells take up glucose from the blood and use it for energy or store it as reserves, which lowers the amount of sugar in the blood after a meal. When the pancreas produces too little insulin, or the body's cells respond to it weakly (insulin resistance), the amount of glucose in the blood rises and type 2 diabetes may develop over time. The blood insulin test is most often done together with a glucose test, so that it is possible to compare how the body responds to insulin and to calculate insulin resistance indices, for example the HOMA-IR index. According to MedlinePlus, the test is useful for finding the cause of low blood sugar (hypoglycaemia), diagnosing insulin resistance, making decisions about type 2 diabetes treatment, and monitoring the results of pancreatic islet cell transplants. Because the amount of insulin in the blood varies considerably depending on when the last meal was, the result must be assessed together with glucose measured at the same time.

• When episodes of low blood sugar (hypoglycaemia) keep recurring and the cause is being looked for
• When insulin resistance is suspected — where there is obesity, high blood pressure or other signs of metabolic syndrome
• When decisions are being made about how to treat type 2 diabetes
• To monitor the results of a pancreatic islet cell transplant
• When an insulinoma is suspected (a pancreatic tumour that produces too much insulin)

Insulin reference ranges depend on the assay method the laboratory uses, so the exact interval has to be read from your own result report, next to the result. MedlinePlus notes that the result should always be assessed together with glucose measured at the same time, because an insulin number on its own, without that context, says very little.

A raised insulin result

Raised insulin may be linked to insulin resistance, where the body's cells respond more weakly to insulin and the pancreas compensates by producing more of it. Other causes are a pancreatic tumour (insulinoma), Cushing's syndrome, or too large a dose of the insulin preparations used to treat diabetes. Glucose assessed at the same time helps establish the exact cause.

Causes of a raised result

• Insulin resistance — cells respond more weakly to insulin
• A pancreatic tumour (insulinoma) producing too much insulin
• Cushing's syndrome
• Too large a dose of the insulin preparations used to treat diabetes

What to discuss with a doctor

• Glucose assessed at the same time — whether the result fits insulin resistance or low blood sugar
• The HOMA-IR index, to assess insulin resistance
• Body mass index, blood pressure and other signs of metabolic syndrome
• Whether the fasting requirement was met at the time of the test

If insulin is low and glucose is high, this may indicate that the pancreas is not producing enough insulin. Possible causes are type 1 diabetes and pancreatitis (inflammation of the pancreas); there are other causes too. The result has to be assessed together with the amount of glucose in the blood.

Causes of a low result

• Type 1 diabetes — the pancreas does not produce enough insulin
• Pancreatitis (inflammation of the pancreas)

What to discuss with a doctor

• The amount of glucose in the blood at the same time
• A C-peptide test — it helps assess how much insulin the pancreas itself is producing
• Symptoms: thirst, frequent urination, tiredness — worth discussing with your doctor
• Further diabetes investigation, if the result together with glucose points that way

How the insulin test differs from a glucose test

A glucose test shows the amount of sugar in the blood, while an insulin test shows how much of the hormone the pancreas released to regulate that sugar. Together, the two tests help assess whether the body responds to insulin effectively, and allow insulin resistance indices such as HOMA-IR to be calculated.

Related pages

• Glucose
• HbA1c
• HOMA-IR index
• C-peptide
• Triglycerides
• Glucose tolerance test