IGFBP-3 IS A POOR PARAMETER FOR ASSESSMENT OF CLINICAL ACTIVITY IN ACROMEGALY

OBJECTIVE Elevated serum IGF-I and IGF binding protein-3 (IGFBP-3) lev els have been found in patients with active acromegaly. We have studie d the relative diagnostic merits of measurements of IGFBP-3 compared w ith IGF-I as a parameter of disease activity in these patients. DESIGN /PATIENTS Thirty untreated patients with acromegaly were compared with 30 healthy adults. MEASUREMENTS Twenty-four-hour sampling for serum G H in patients with acromegaly, serum IGF-I and IGFBP-3. RESULTS Mean I GF-I levels were 22.0 nmol/l (range 6.5-38.4) in the healthy adults an d 118.7 nmol/l (range 67.7-206.0) in patients with acromegaly. Mean IG FBP-3 levels were 3.5 mg/l (range 2.1-4.8) in controls and 5.4 mg/l (r ange 4.2-6.6) in patients with acromegaly. Mean IGF-I/IGFBP-3 ratios w ere 6.5 nmol/mg (range 1.9-14.5) in the healthy adults and 22.0 nmol/m g (range 14.3-32.7) in patients with acromegaly. There was a considera ble overlap for IGFBP-3 levels but not for IGF-I levels, between norma ls and acromegalics. The IGF-I/IGFBP-3 ratio also showed overlap betwe en normals and acromegalics. There was a significant correlation betwe en the mean 24-hour GH and IGFBP-3 levels (P=0.036) and between the IG F-I and IGFBP-3 levels (P<0.002) in acromegaly. In patients with acrom egaly, the IGFBP-3 levels showed a decrement, but the IGF-I/IGFBP-3 ra tio did not change significantly with age. CONCLUSIONS IGFBP-3 has no additional discriminatory value over IGF-I measurements for the assess ment of clinical activity in acromegaly. In acromegaly, IGFBP-3 decrea ses with increasing age. In acromegaly, IGFBP-3 levels significantly c orrelate with mean 24-hour GH levels and IGF-I levels.