Serum Insulin-Like Growth Factor I Reference Values for an Automated Chemiluminescence Immunoassay System: Results from a Multicenter Study

Abstract

Background: Analysis of insulin-like growth factor I in serum (S-IGF-I) is an integral component in the diagnosis of GH-related disorders and is going to be of interest in the diagnosis and follow-up of many disorders. The objective of the present study was to develop cross-sectional reference values for S-IGF-I measured by an automated chemiluminescence immunoassay (Nichols Advantage^®). Methods: The study included samples from 3,961 healthy subjects (2,201 males, 1,760 females) aged 1 month to 88 years. Six laboratories were involved in this study and the samples were analyzed by one of seven automated immunoassay systems run in these laboratories. For data analysis, polynomial age and sex-specific models were fitted after transformation of S-IGF-I values. Results: The results show the well-known age dependency of S-IGF-I levels. At ages <20, higher S-IGF-I levels were seen in girls with an estimated mean peak of 410 µg/l at age 14 and an estimated mean peak of 382 µg/l at age 16 in boys. Thereafter, a rapid decrease was seen to approximately 25 years of age, followed by a slow age-dependent decrease. In adulthood, S-IGF-I in males were slightly, but significantly higher than in females. It could be shown that the mean values of some reference sample subgroups differed significantly from the total mean. However, the multicenter approach used in this study reduces the impact of systematic population, sample handling and laboratory differences on the calculated reference mean. Conclusion: The present study establishes age- and sex-specific reference values for a fully automated immunoassay system based on a large population of healthy subjects. The established reference values may be used for this immunoassay system in different laboratories provided that the systematic difference between systems is low.

Health-related quality of life in acromegalic subjects: data from AcroBel, the Belgian Registry on acromegaly

“…This is the first study to report on the use of AcroQoL in a nationwide registry with controlled and uncontrolled patients. Median AcroQoL total and subscores are comparable with those reported earlier for acromegalic patients in remission (5,7,14,20,21), and higher than that in active acromegaly (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

“…All measurements were completed at the end of the survey period in two consecutive runs for GH and in one run for IGF-I. IGF-I values were compared with age-and gender-specific reference ranges (10) and were expressed as a z-score (normal range K2 to C2).…”

Normal values of serum IGF-1 in adults: results from a Brazilian population

“…Ten groups divided according to age [5-year intervals (7,8)] were pre-defined, with 100 subjects per group (6,17). Since the need of different reference values for men and women is not clear (6), each group was divided into two subgroups (50 men and 50 women).…”

“…The values should be assay-specific (9,10), should be reported according to age (7)(8)(9)(10)(11)(12)(13)(14)(15)(16), and should preferentially be population-specific (17). The sample from which these values are extracted should be of adequate size (7,9) and the subjects should be selected rigorously, excluding conditions known to interfere with the levels of this hormone (6). It is also important to know which variations in IGF-1 levels can be attributed to the treatment implemented or to progression of the disease and are not only due to interassay variability (18).…”

Labordiagnostik bei Wachstumshormon-assoziierten Erkrankungen/Biochemical diagnosis of growth hormone related diseases

“…Die Erstellung guter Referenzbereiche f ü r IGF-I ist jedoch sehr aufw ä ndig [42] , da es einer starken Altersabh ä ngigkeit unterliegt. Zudem m ü ssen f ü r Kinder zwischen 6 und 18 Jahren auch geschlechtsspezifi sche Referenzbereiche erstellt werden.…”