Serum insulin-like growth factor-I measurement in the follow-up of treated acromegaly: Comparison of four immunoassays

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

“…The maximum difference in the upper limit (97.5th percentile) was 7 µg/L (20 to 30 years) and the maximum difference in the lower limit (2.5th percentile) was 10 µg/L (21 to 25 years). Therefore, similar to previous studies (7)(8)(9)(10)(11)(12)(13)(14), the IGF-1 reference values are reported according to age group, without distinction between genders ( Table 2). The curves representing the 97.5th, 50th (median) and 2.5th percentiles of IGF-1 as a function of age are shown in figure 1.…”

“…Because IGF-1 values were not normally distributed in the study population, the reference range was defined as follows : 1) 2) logarithmic transformation of the values obtained, calculation of the mean ± 2 SD of these values, and exponentiation to obtain the limits corresponding to the original scale (7)(8)(9)(10)12). The Student t-test and Kruskal-Wallis test were used to determine differences between groups according to gender (10)(11)(12)14).…”

“…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).…”

Classification of Patients With GH Disorders May Vary According to the IGF-I Assay

“…However, even when using kits that are calibrated against the same international standard, and the same method to remove IGF-I binding proteins, patient classification in terms of IGF-I categories remains variable (7)(8)(9)(10). We suspected that a potential reason for these discrepancies was the use of different reference values.…”

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

“…Verschiedene Studien konnten jedoch zeigen, dass die Qualit ä t der Referenzbereiche entscheidend von der Gr ö ß e des zugrundeliegenden Referenzkollektivs abh ä ngt. Die Verwendung von Referenzbereichen, die entweder nicht methodenspezifi sch oder aber an zu kleinen Kollektiven erstellt wurden, f ü hrt daher immer wieder zu klinischen Fehlinterpretationen [43] . Die Laboratorien sollten daher von den Herstellern der IGF-I-Assays Auskunft ü ber Gr ö ß e und genaue Charakterisierung der den methodenspezifi schen Referenzbereichen zugrundeliegenden Referenzkollektive verlangen.…”