Comparison of acid ethanol extraction and acid gel filtration prior to IGF-I and IGF-II radioimmunoassays: improvement of determinations in acid ethanol extracts by the use of truncated IGF-I as radioligand.
Insulin-like growth factor binding proteins interfere in the IGF-I and -II radioimmunoassays. In an attempt to overcome this problem, we have compared the use of truncated IGF-I, with reduced IGFBP affinity, and IGF-I as radioligands for IGF-I RIA measurements in serum separated by acid gel filtration or acid ethanol extraction followed by cryo-precipitation. With truncated IGF-I as radioligand the IGF-I measurements in acid gel filtrates and acid ethanol extracts were significantly correlated in healthy subjects (N = 42, r = 0.91, p less than 0.001) and in patients with acromegaly (N = 10, r = 0.85, p less than 0.01), GH deficiency (N = 10, r = 0.88, p less than 0.001) or Type I diabetes mellitus (N = 10, r = 0.90, p less than 0.001). In contrast, the IGF-I concentrations in acid ethanol extracts determined with IGF-I as radioligand did not correlate with those in acid gel filtrates using truncated IGF-I radioligand in patients with acromegaly (r = 0.61, NS) or GH deficiency (r = 0.46, NS). In the latter group the mean IGF-I concentrations measured in acid ethanol extracts were erroneously elevated by 112%. Low-affinity antibodies used for IGF-II RIA determinations failed to give reliable results in acid ethanol extracts from patients with Type I diabetes mellitus or GH deficiency. In conclusion, erroneously high IGF-I concentrations owing to binding of the radioligand to IGFBPs not completely removed by acid ethanol extraction can be avoided by the use of truncated IGF-I as radioligand.
Bang
P
P
Department of Endocrinology, Karolinska Institute, Stockholm, Sweden.
Eriksson
U
U
Sara
V
V
Wivall
I L
IL
Hall
K
K
D000172:Acromegaly / Q000097:blood; D000328:Adult; D002850:Chromatography, Gel; D003922:Diabetes Mellitus, Type 1 / Q000097:blood; D000431:Ethanol; D005260:Female; D013006:Growth Hormone / Q000172:deficiency; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000032:analysis* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000378:metabolism; D011863:Radioimmunoassay; D011994:Recombinant Proteins
D010446:Peptide Fragments; D011994:Recombinant Proteins; D000431:Ethanol; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone