Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
IGF-1 is a 70 amino acid straight chain peptide of molecular weight 7649 Daltons. It is part of a family of growth factors which include IGF-1 and IGF-2 . IGF-1 is highly basic in nature and circulates bound to high molecular weight IGF-binding proteins (IGFBP-1 to -6), which help to modulate IGF-1 action. IGF-1 mediates the growth promoting action of growth hormone (GH), being released from a variety of body tissues (predominantly the liver) in response to GH. <br /> IGF-1 is used as an index of GH secretion in the diagnosis of GH-deficiency and excess, as well as monitoring of treatment of these disorders. The half-life of IGF-1 is approximately 15 hours and so is not affected by short-term variation in GH secretion. IGF-1 is recommended as an initial screening test for acromegaly but has limitations as a standalone diagnostic test, particularly in the diagnosis of growth hormone deficiency and dynamic function tests are often required to confirm or exclude GH deficiency/excess. Other than GH, the most important factors influencing IGF-1 concentration are age and gender. Peak levels occur during adolescence and are lowest at birth. It is therefore important to use gender and age related reference ranges.
Specimen container paediatric:
serum/lithium heparin plasma/EDTA plasma
Specimen container adult:
serum/lithium heparin plasma/EDTA plasma
Minimum volume paediatric:
1 mL blood
Minimum volume adult:
2 mL blood
Special requirements:
If samples are not to be despatched within 24 hours, suggest store at -20°C.
Sample stability:
Unseparated:
Same day (ideally separate within 2 hours)
Separated:
3 days at 20 to 25°C,
3 days at 2 to 8°C,
1 month at -20°C
Transport requirements:
Ambient
Interpretation:
The majority of patients with acromegaly have a raised serum IGF-1 concentration (when appropriate age-related reference ranges are used). However, false positives can occur particularly in pregnancy and late adolescence. Importantly IGF-1 concentrations may be affected by hepatic or renal failure, hypothyroidism, malnutrition, severe infection and poorly controlled diabetes. Confirmation of a biochemical diagnosis of growth hormone excess requires measurement of GH in response to the oral glucose tolerance test. Measurement of IGF-1 also has a role in monitoring patients treated for acromegaly with normalised IGF-1 concentrations often one of the treatment goals.
Although a low IGF-1 (in the absence of factors such as liver disease, poorly controlled diabetes) provides evidence of growth hormone deficiency, an IGF-1 concentration within the reference range cannot be used to exclude the diagnosis. GH measurement during dynamic function testing is usually required to diagnose/exclude growth hormone deficiency.
Reference ranges:
Detailed age-related reference ranges are available. Relevant ranges will be included with reports.
An IGF-1 SD-score spreadsheet is available, which can be used to calculate age/gender specific SD-scores and percentiles.
Factors affecting result:
Gross haemolysis, lipaemia or icterus may interfere.
Heterophilic antibodies can interfere with immunoassays.
Other info:
EDTA and Lithium heparin anticoagulated sampes are also acceptable.