The role of IGF binding protein-3 as a parameter of activity in acromegalic patients.
OBJECTIVE
The production of insulin-like growth factor binding protein-3 (IGFBP-3), the main IGF-I binding protein, is regulated by GH, and its serum levels are increased in acromegaly. We investigated its potential value as a parameter of acromegaly activity or remission in comparison with IGF-I, taking GH suppression below 2 microg/l after glucose load as the normal standard.


METHODS
Data from 40 acromegalic patients (12 males and 28 females, aged 28 to 79 years) were obtained retrospectively from stored samples. From these, 145 pairs of IGF-I/IGFBP-3 values were collected; in 67 of them, simultaneous measurement of GH after glucose loading allowed their classification as active or inactive acromegaly. Relationships between IGF-I, IGFBP-3 and GH after glucose load were assessed, as well as differences between IGF-I and IGFBP-3 levels in active and inactive acromegaly.


RESULTS
Significant positive correlation between IGF-I and IGFBP-3 in 145 samples was observed (r=0.49, P<0. 0001). As for the 67 samples in which activity or remission could be defined in terms of GH after glucose load, 50 were active and 17 inactive. Both IGF-I and IGFBP-3 significantly correlated with minimum GH (r=0.53, P<0.0001 and r=0.41, P<0.001 respectively). For both parameters, significant differences of means between active and inactive cases were observed (623+/-296 vs 300+/-108 ng/ml, P<0.0001 for IGF-I, and 4.1+/-1.3 vs 3.2+/-0.9 microg/ml, P<0.006 for IGFBP-3). Yet, when comparing in individual cases their classification as active or inactive with the finding of normal or increased IGF-I and IGFBP-3, among active cases 16% appeared as normal according to IGF-I, and 50% appeared as normal in terms of IGFBP-3. Among inactive cases, 23.5% appeared as active according to IGF-I, while 17.5% appeared as active in terms of IGFBP-3.


CONCLUSIONS
Even though IGFBP-3 reflects GH secretion, it offers no advantage over IGF-I in the assessment of acromegaly, and it may underestimate disease activity in acromegalic patients.
Halperin
I
I
Department of Endocrinology, Hospital Clinic, Barcelona University, Spain. ihalperi@medicina.ub.es
Casamitjana
R
R
Flores
L
L
Fernandez-Balsells
M
M
Vilardell
E
E
D000172:Acromegaly / Q000097:blood*; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood*; D005260:Female; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies
D015415:Biomarkers; D018972:Insulin-Like Growth Factor Binding Protein 3; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I