Insulin-like growth factor 1 (IGF-1), a polypeptide hormone produced by the liver and other tissues, mediates GH activity and glucose metabolism. It is carried in the blood and is bound to a protein carrier that prolongs its half-life.

This test is used to monitor the growth of children as well as to diagnose acromegaly and hypopituitarism. Normal IGF-1 results rule out a deficiency of GH. Testing of IGF-1 is preferable to GH tests because its levels are more constant. IGF-1 is also a reliable nutrition index, having a low value for anorexia or malnutrition.

See Table 6.8.

1. Preferably, the patient should be fasting. Obtain a 5-mL plasma venous blood sample using EDTA anticoagulant. Serum may also be used. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

2. Chill blood-drawing tubes before and place on ice immediately after obtaining the specimen. Spin the sample in a refrigerated centrifuge. Freeze if not analyzing immediately.

1. Increased IGF-1 levels are associated with the following conditions:

   1. Acromegaly (some cases), gigantism

   2. Hypoglycemia associated with non–islet cell tumors

   3. Hepatoma

   4. Wilms tumor (a rare kidney cancer that most commonly occurs in children)

   5. Precocious puberty

2. Decreased IGF-1 levels are associated with the following conditions:

   1. Dwarfism (short stature)

   2. Hypopituitarism

   3. Hypothyroidism

   4. Puberty delay

   5. Laron dwarfism (autosomal recessive disorder, not responsive to GH)

   6. Cirrhosis of liver and other hepatocellular diseases

   7. Malnutrition and anorexia

   8. Diabetes (diabetic retinopathy)

   9. Emotional deprivation syndrome (maternal deprivation)

Pretest Patient Care

1. Explain test purpose and procedure. Fasting is not required.

2. Do not administer radioisotopes within 1 week of testing.

3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.