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 supression below 2 mu g/l after glucose load as the normal standa rd. Methods: Data from 40 acromegalic patients (12 males and 28 females, aged 2 8 to 79 years) were obtained retrospectively from stored samples. From thes e, 145 pairs of IGF-I/IGFBP-3 values were collected: in 67 of them, simulta neous 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 a nd 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 act ivity or remission could be defined in terms of GH after glucose load, 50 w ere 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 b oth parameters, significant differences of means between active and inactiv e cases were observed (623+/-296 vs 300+/-108 ng/ml, P<0.0001 for IGF-I, an d 4.1+/-1.3 vs 3.2+/-0.9 mu g/ml, P<0.006 for IGFBP-3). Yet, when comparing in individual cases their classification as active or inactive with the fi nding of normal or increased IGF-I and IGFBP-3, among active cases 16%; app eared 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. Conclusion: Even though IGFBP-3 reflects GH secretion, it offers no advanta ge over IGF-I in the assessment of acromegaly, and it mag underestimate dis ease activity in acromegalic patients.