Table 1.

Characteristics of the tested IGF-I assays as provided by the manufacturers. The limit of quantification (LOQ) is the lowest amount of IGF-I that can be accurately quantified with an allowable error of ≤20%. The limit of detection (LOD) is the IGF-I concentration corresponding to the 95th percentile value from a number of determinations of IGF-I concentration in free serum samples.

Name of the assay	Manufacturer	Automated	Tracer	International standard against which the assay is calibrated	Intra-assay CV	Inter-assay CV	LOQ or LOD in ng/mL	Highest measurable value without dilution (ng/mL)	Reference adult population recruited by the manufacturer
Elecsys® IGF-1	Roche Diagnostics	Yes	Ruthenium	WHO international standard 02/254	Human samples between 1.4 and 3.5%	Human samples between 2.5 and 4.6%	LoQ 15 ng/mL LoD 7 ng/mL	1600 ng/mL	3652 men between 3 months and 80 years 3046 women between 3 months and 80 years
IMMULITE® 20000 IGF-I	Siemens	Yes	Phosphatase alcaline	WHO international standard 02/254	Human samples between 2.4 and 6.3%	Human samples between 3 and 7.6%	LoQ 24.9 ng/mL LoD 13.3 ng/mL	90,000 ng/mL	701 pediatric and 1104 adult samples