26858 Insulin-Like Growth Factor 1, Serum (IGF1S)

IGF (Insulin-L​ike Growth Factor)

IGF-1

IGF1

Insulin Like Growth Factor I

Somatomedin-C​

First-tier test for evaluation of growth disorders

Evaluation of growth hormone deficiency or excess in children and adults

Monitoring of recombinant human growth hormone treatment

Follow-up of individuals with acromegaly and gigantism

​Necessary Information: Indicate patient's age and sex. ​

For 12 hours before specimen collection, patient should not take multivitamins or dietary supplements (eg, hair, skin, and nail supplements) containing biotin (vitamin B7).

Centrifuge and aliquot serum into a plastic vial. ​

Gross hemolysis

Gross icterus

Insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 3 (IGFBP3) reference ranges are highly age dependent, and results must always be interpreted within the context of the patient's age.

Increased concentrations of IGF1 are normal during pregnancy, however reference intervals on this population have not been formally established.

Discrepant IGF1 and IGFBP3 results can sometimes occur due to liver and kidney disease; however, this is uncommon and such results should alert laboratories and physicians to the possible occurrence of a preanalytical or analytical error.

The use of biotin-containing supplements may lead to inaccurately reduced IGF1 measurements.

Currently, IGF1 or IGFBP3 cannot be reliably used as risk indicators or prognostic markers in breast, colon, prostate, or lung cancer.

Insulin-like growth factor 1 and IGFBP3 assays exhibit  variability among platforms and manufacturers. Results obtained with different assay methods or kits should not be used interchangeably.

​All immunometric assays can, on rare occasions, be subject to a hooking effect at extremely high analyte concentrations (falsely low results) or heterophilic antibody interference (most often falsely high results).  If the laboratory result does not fit the clinical picture, these possibilities should be considered.

Both insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 3 (IGFBP3) measurements can be used to assess growth hormone (GH) excess or deficiency. However, for all applications, IGF1 measurement has generally been shown to have superior diagnostic sensitivity and specificity and should be used as the primary test. In particular, in the diagnosis and follow-up of acromegaly and gigantism, IGFBP3 measurement adds little if anything to IGF1 testing. The combination of IGF1 and IGFBP3 measurements appears superior to determining either analyte alone in the diagnosis of GH deficiency and resistance, and in the monitoring of recombinant human GH (rhGH) therapy.

Insulin-like growth factor 1 and IGFBP3 levels below the 2.5th percentile for age are consistent with GH deficiency or severe GH resistance, but patients with incomplete GH deficiency or mild-to-moderate GH resistance may have levels within the reference range. In GH deficiency, GH levels may also be low and can show suboptimal responses in stimulation tests (eg, exercise, clonidine, arginine, ghrelin, growth hormone-releasing hormone [GHRH], insulin-induced hypoglycemia), while in severe GH resistance, GH levels are substantially elevated. However, dynamic GH testing is not always necessary for diagnosis. If it is undertaken, it should be performed and interpreted in endocrine testing centers under the supervision of a pediatric or adult endocrinologist.

The aim of both pediatric and adult GH replacement therapy is to achieve IGF1 and IGFBP3 levels within the reference range, ideally within the middle-to-upper third. Higher levels are rarely associated with any further therapeutic gains but could potentially lead to long-term problems of GH excess.

Elevated IGF1 and IGFBP3 levels support the diagnosis of acromegaly or gigantism in individuals with appropriate symptoms or signs. In successfully treated patients, both levels should be within the normal range. In both diagnosis and follow-up, IGF1 levels correlate better with clinical disease activity than IGFBP3 levels.

After transsphenoidal removal of pituitary tumors in patients with acromegaly, IGF1 concentration starts to decrease and returns to normal levels in most patients postoperatively by the fourth day.(1)

Individuals with anorexia or malnutrition have low values of IGF1. IGF1 is a more sensitive indicator than prealbumin, retinol-binding protein, or transferrin for monitoring nutritional repletion.