From the Guidelines
To test for IGF-1, a blood test measuring serum IGF-1 levels in relation to age-adjusted, sex-adjusted, and Tanner stage-matched normal ranges is the recommended approach 1.
Key Considerations for Testing
- The test should be interpreted with caution, especially in adolescents during the peak growth spurt, as marginal or mild elevations may not accurately indicate GH excess 1.
- Factors such as severe hypothyroidism, malnutrition, severe infection, poorly controlled diabetes mellitus, hepatic and/or renal failure, and oral oestrogens can confound IGF-1 test results 1.
Procedure and Interpretation
- A blood sample is taken after fasting for a specified period, and the serum IGF-1 level is measured and compared to established reference ranges for age, sex, and Tanner stage 1.
- Elevated IGF-1 levels can indicate GH excess, but additional tests such as an oral glucose load to assess GH suppression may be necessary for a definitive diagnosis 1.
Clinical Context
- The diagnosis of GH excess should consider clinical assessments of phenotype, including height velocity, pubertal stage, and bone age, alongside biochemical results 1.
- Monitoring both GH and IGF-1 levels at baseline and during follow-up is crucial for managing GH excess in children and adolescents 1.
From the Research
Testing for IGF-1
To test for Insulin-like Growth Factor 1 (IGF-1), several methods are available, including:
- Immunoassays: These rely on antibody specificity towards IGF-1 and differential cross-reactivity towards IGF binding proteins (IGFBPs) 2.
- Mass spectrometry (MS): This includes techniques such as liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography high-resolution accurate-mass mass spectrometry (LC-HRAMS) 2.
- Radioimmunoassay (RIA): This method has been used to measure IGF-1 in various studies 3, 4.
- Enzyme-linked immunosorbent assay (ELISA): This method has been validated for measuring IGF-1 in serum and plasma samples 4.
Considerations for IGF-1 Testing
When testing for IGF-1, it is essential to consider the following:
- IGF-1 circulates as a ternary complex bound to its principal carrier/binding protein, IGFBP3, and acid-labile subunit (ALS), which can interfere with immunoassays 2.
- Different assay kits can give varying results for a given sample, highlighting the need for standardization and harmonization of immunoassay parameters 5, 3.
- The choice of assay method may depend on the specific application, such as screening for hypersomatotropism in diabetic cats 4 or measuring IGF-1 in relation to prostate cancer and benign prostatic hyperplasia 6.
Available Assays
Several commercial IGF-1 assay kits are available, including:
- iSYS
- LIAISON XL
- IMMULITE
- IGFI RIACT
- Mediagnost ELISA
- Mediagnost RIA 5. Each kit has its own characteristics, and the choice of kit may depend on the specific requirements of the study or clinical application.