IGF-I ELISA

A non-extraction assay with
high specificity

The measurement of insulin-like growth factor-I (IGF-I) in serum is of especially high utility in the diagnostic work-up of growth disturbances, particularly with regard to human growth hormone (hGH) deficiency or acromegaly. The most important advantage of measuring IGF-I over hGH are its stable circadian levels, i.e. even a single measurement is of conclusive significance.

In view of the above, measurement of IGF-I should be put on the front burner in laboratory diagnostic work-up.

The advantages of our ELISAs are:

• non-extraction assay;
• high specificity for IGF-I;
• no interference from IGF-binding proteins (IGFBP);
• only a sample volume of 10 µL required;
• one sample dilution suffices (usually 1:21);
• calibrated against the international standard of WHO NIBSC 02/254;
• very high sensitivity (0.09 ng/mL);
• outstanding accuracy -- 98.7% recovery;
• remarkable precision: inter-assay variance of 6.8% and intra-assay variance of 6.7%.

IBL International´s IGF-I enzyme linked immunosorbent assay (ELISA) by IBL International is used for measuring IGF-I in human serum/plasma, cerebrospinal fluid and other body fluids as well as in conditioned cell culture media of many human cell lines.

What is more, the assay can also be used for the measurement of IGF-I in other mammals such as primates, cattle, pig, sheep, horse, donkey, goat, dog, cat, rabbit and guinea pig. However, the kit is not suited for rat, mouse and chicken samples

Insulin-like growth factors I and II (IGF-I, IGF-II) play a key role in proliferation, differentiation and specific functions of many cell types. IGF-I is identical to somatomedin C (Sm-C) and is regulated by the growth hormone (hGH/GH) and nutrition. Unlike many other peptide hormones, IGFs are bound to specific binding proteins (IGFBP) with a high affinity. A substantial problem in the measurement of IGF-I levels is the interference by IGFBPs. When measured in untreated serum samples, inaccurate results are obtained due to the extremely slow dissociation of the IGF-I/IGFBP-3 complex during assay incubation. For this reason, only a fraction of IGF-I is available for measurement. Interferences are determined by the IGF-I to IGFBP ratio in the sample.

In order to circumvent this problem, a simple assay was developed in which samples are acidified and diluted using a buffer of a special composition prior to performing ELISA.

Clinical Significance

Apart from hGH, a number of other factors affect serum IGF-I levels. Low values are found in malnutrition/malabsorption, hypothyroidism, liver disease, untreated diabetes mellitus, chronic inflammatory diseases, malignancies and multiple trauma. Elevated levels, on the other hand, are found in precocious puberty and obesity.

In order to be able to correctly interpret IGF measurements, it is of utmost importance to consider the age-dependent pattern of IGF-1 levels, which you can find in the Instruction for Use.

Percentiles
Pubertäts stadium	0.1th	5th	50th	95th	Pubertal Stage
1	61	105	186	330	1
2	85	156	298	568	2
3	113	196	352	631	3
4	171	268	431	693	4
5	165	263	431	706	5