insulin assay
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p542-543
2025-06-22
378
Type of test Blood
Normal findings
6-26 μU/mL or 43-186 pmol/L (SI units)
Newborn: 3-20 μU/mL
Possible critical values > 30 μU/mL
Test explanation and related physiology
Insulin assay is used to diagnose insulinoma (tumor of the islets of Langerhans). It is also used in the evaluation of patients with fasting hypoglycemia.
Some investigators believe that measuring the ratio of the blood sugar and insulin on the same specimen obtained during the oral glucose tolerance test is more reliable than measuring insulin levels alone. Combined with the oral GTT, the insulin assay can show characteristic curves. For example, patients with juvenile diabetes have low fasting insulin levels and display flat GTT insulin curves because of little or no increase in insulin levels. Patients who have mild cases of diabetes have normal fasting insulin levels and display GTT curves with a delayed rise.
Type 2 diabetes (adult onset) is characterized by an excess of insulin production in response to GTT. This hyperresponse of insulin may precede hyperglycemia by many years, allowing the patient time and opportunity to take action to reduce the incidence of outright diabetes through diet management and lifestyle changes.
When combined with fasting blood sugar, the insulin assay is very accurate in detecting insulinoma. After the patient fasts 12 to 14 hours, the insulin/glucose ratio should be less than 0.3. Patients with insulinoma have ratios greater than this. To increase the sensitivity and specificity of these combined tests for insulinoma, Turner and others have proposed the amended insulin/glucose ratios using variable mathematical fudge factors:
A Turner-amended ratio of more than 50 suggests insulinoma.
Interfering factors
• Antiinsulin antibodies can interfere with radioimmunoassay.
• Food intake and obesity may cause increased insulin levels.
* Drugs that may cause increased insulin levels include corticosteroids, levodopa, and oral contraceptives.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: yes
• Blood tube commonly used: red
• If the serum insulin level will be measured during the GTT, collect the blood sample before oral ingestion of the glucose load and often at designated intervals after glucose ingestion.
Abnormal findings
Increased levels
- Insulinoma
- Cushing syndrome
- Acromegaly
- Obesity
- Fructose or galactose intolerance
Decreased levels
- Diabetes mellitus
- Hypopituitarism
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