Insulin

INSULIN

What is Insulin?


Insulin is defined as “a hormone that has extensive effects on metabolism and other body functions, such as vascular compliance. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy source.” (Wikipedia 2009)

Photo by: http://www.chemlin.net/news/2006/oct2006/human-insulin-degrading-enzyme.htm

Testing for Insulin Levels

Testing for insulin is done using a radioimmunoassay that gives a quantitative analysis of serum insulin levels.

Patient Preparation:

• Patient should fast from all foods and fluids except water for 10-12 hours prior to testing.
  

Procedure and Posttest Care:

1. Obtain 5mL of blood from a fasting person, serum is preferred. Observe standard precautions.


2. Instruct patient that he/she may resume from his/her usual activities after the test.

Interfering Factors:

1. Oral hypoglycemic agent ingestion or injection causes elevated insulin levels.


2. Oral contaceptives and other drugs cause falsely elevated values.


3. Recently administered radioisotopes affect test results.


4. In the second to third trimester of pregnancy, there is a relative insulin resistance with a progressive decrease of plasma glucose and immunoreactive insulin.


5. Agitation and stress.


6. Hemolysis due to rough handling of the sample.
   

Reference Values:

NORMAL:

Immunoreactive
Adults: 0-35 IU/mL or 0-243 pmol/L

Children: 0-10 IU/mL or 0-69 pmol/L

Free
Adults: 0-17 IU/mL or 0-118 pmol/L

Children (prepubertal): 0-13 IU/mL or 0-90 pmol/L

Clinical Implications:

1. Increased insulin levels:

• Insulinoma
  
• Type 2 diabetes mellitus, untreated


• Acromegaly


• Cushing's syndrome


• Endogenous administration of insulin (factitious hypoglycemia)


• Obesity (most common cause)


• Pancreatic islet cell hyperplasia
  

2. Decreased insulin levels:

• Type 1 diabetes mellitus (severe)
  
• hypopituitarism
  

References:

• A Manual of Laboratory and Diagnostic Tests 7th Edition By: Frances Fischbach
  
• Prof. Guide to Diagnostic Tests
  
• http://wikipedia.com