Laboratory investigation of acromegaly: Is basal or random GH > 0.4 µg/L in the presence of normal serum IGF-1 an important result?

OBJECTIVE: To determine the frequency of indication of the GH suppression test and pituitary magnetic resonance imaging (MRI) in patients with clinical suspicion of acromegaly with GH concentrations > 0.4 µg/L despite normal serum IGF-1. SUBJECTS AND METHODS: A total of 160 patients with clinical suspicion of acromegaly with normal IGF-1 were studied. RESULTS: Basal GH > 0.4 µg/L was observed in 70/88 women (79.5%). Nadir GH > 0.4 µg/L was found in 21/70 women (30%) and these patients were submitted to MRI, which revealed a microadenoma in 2/21 women (9.5%). In these two women, IGF-1 continued to be normal in subsequent measurements and no clinical progression has been observed so far (time of follow-up until now 4 years). Basal GH > 0.4 µg/L was seen in 33/72 men (45.8%). Nadir GH was < 0.4 µg/L in all of them. CONCLUSIONS: In patients with clinical suspicion of acromegaly, concern over GH concentration in the presence of normal IGF-1 results in the unwarranted complementary investigation in many cases, and even in possible equivocal diagnoses. It is only in exceptional cases that normal IGF-1 should not rule out acromegaly.