Treatment with hormone analogues can challenge the precise measurement by interference with the routinely used immunoassays systems, related to the presence of autoantibodies in the serum, interference with associated therapy or the presence of altered forms of the hormone, with modified biological activity and/or immunoreactivity.
In patients with acromegaly treated with the hGH antagonist Pegvisomant (PEG; Somavert), most of the assays are deeply influenced. The current recommendation for assessing secretion status in this setting is by basal IGF1 assays.
In our study, we performed hGH measurement during OGTT or in a four-points day curve. Six acromegalic patients, four of them treated with 1030 mg PEG s.c. daily, and two without PEG were evaluated using the following methods:
i) 125I-IRMA HGH MAIA Clone (ADALTIS Italy), a liquid phase reaction immunoassay with magnetic separation of antibodyantigen125I antibody complex, not corrected for B2036-PEG cross-reactivity (n=33 samples).
ii) 125I-IRMA HGH CT (ADALTIS Italy), a two-site immunoassay, with a solid phase reaction on tubes coated with antibodyantigen125I antibody complex (n=50 samples).
In patients without PEG treatment, the correlation between GH values with the two assays was 0.91 and 0.99. In patients treated with PEG, all values obtained with the first method were under the detection limit (<0.5 ng/ml). GH levels obtained with the second method were related with the tumor status of each patient, in four out of seven set of data being in a similar range to GH levels before PEG treatment, in two lower and in one higher (P<0.05). It seems that the second assay does not interfere with B2036-PEG, possibly due to the fact that in this method serum GH, but not PEG, binds directly to the anti-GH antibody that is coated on the tube.
In conclusion, hGH assays in acromegalic patients treated with Pegvisomant must be carefully checked for being appropriate for this specific clinical setting.