Insulin

Insulin may be used, often along with glucose and C-peptide levels, to help diagnose insulinomas and to help determine the cause of hypoglycaemia (low blood glucose). Insulin and C-peptide levels also may be used to monitor the amount of insulin produced by the body (called 'endogenous' insulin), to check if the body is not responding to insulin properly (called 'insulin resistance'), and to help determine when a type 2 diabetic might need to start taking insulin injections to supplement oral medications.

Insulin levels are sometimes used in conjunction with the glucose tolerance test (GTT). Blood glucose and, sometimes, insulin levels are measured to evaluate insulin resistance, particularly in obese individuals.

Insulin levels are most frequently requested following an abnormal glucose test and/or when a patient has short- or long-term symptoms of hypoglycaemia, such as sweating, palpitations, hunger, confusion, visual problems, and seizures (although these can be caused by other conditions). 

Insulin and C-peptide are produced by the body at the same rate. Both may be requested to evaluate how much insulin in the blood is due to endogenous production (what your body is making) and how much is from exogenous (produced outside the body, e.g. injected) sources. Insulin tests will reflect the total, while C-peptide will reflect only the endogenous insulin.

Your doctor also may request both tests to check that an insulinoma has been successfully removed. If you are one of the few people who have received a pancreas cell transplant to restore your ability to produce insulin, your insulin level may be monitored to determine whether or not this procedure is successful over time.

Insulin levels must be evaluated in context. If fasting insulin and glucose levels are normal, most likely the body's glucose regulation system is functioning normally. If insulin is raised and glucose is normal and/or moderately raised, then there may be some insulin resistance. If the insulin is low and the glucose is high, then most likely there is insufficient insulin being produced by the body. If insulin levels are normal or raised and glucose levels are low, then the patient is hypoglycaemic due to excess insulin.

Raised insulin levels may be seen with:

1. Acromegaly
2. Cushing's syndrome
3. Drugs such as corticosteroids, levodopa, oral contraceptives
4. Fructose or galactose intolerance
5. Insulinomas
6. Obesity
7. Insulin resistance, such as appears in early type 2 diabetes

Decreased insulin levels are seen with:

1. Diabetes
2. Hypopituitarism

Insulin for injection used to come strictly from animal sources (cow and pig pancreas cells). Now, most insulin is made by biochemical synthesis to identically match the insulin produced by human beta cells.

There are different pharmaceutical preparations of insulin with different properties.  Some are quick-acting with a short duration and others are time-release preparations that take longer and last longer. Diabetics may take mixtures and/or different types of insulin throughout the day.

Different insulin tests are not identical in the way that they measure insulin.  There are differences in how well they can detect the different kinds of insulin.  If your insulin result is not what your doctor was expecting, he or she may want to talk to the laboratory that performed your test about the types of insulin you are taking.  If you are going to have several insulin tests done, they should be performed by the same laboratory to ensure consistency.

If you have developed anti-insulin antibodies, they will interfere with your test and need to be removed before an accurate insulin level can be measured.  If you have these antibodies against insulin, your doctor may want to measure them whenever you have an insulin test done and whenever they contemplate changing your type of insulin medication.