Spontaneously occurring anti-PTH autoantibodies must be considered in the differential diagnosis of patients with elevated serum PTH levels

We investigated the cause of elevated immunoreactive circulating parathyroi d hormone (PTH) levels in two females of 41 (case 1) and 39 (case 2) years of age with low/normal serum calcium levels and hypocalcemia, respectively, and, in the latter case, hyperprolactinemia. Serum samples from both patie nts were fractionated by Sephadex G-100 Superfine chromatography. Fractions were assayed for PTH and prolactin (PRL) by immunoradiometric assays (IRMA ) and for immunoglobulin G (IgG) by radial immunodiffusion. Sera from both patients were incubated with protein A and protein G Sepharose, centrifugat ed and the supernatant was assayed for PTH by IRMA. Sera were also subjecte d to affinity chromatography with an anti-human-IgG-agarose column. IgG and PTH or PRL were measured in the fractions by radial immunodiffusion and IR MA, respectively. In both cases the majority of serum PTH immunoreactivity eluted in the same fractions of IgG after gel filtration and was precipitat ed by protein A (89% in patient 1 and 96% in patient 2) and protein G (83% in patient 1 and 100% in patient 2), thus, behaving as IgG. In case 1, 79% of PTH was also retained by an anti-hIgG agarose column. High PRL severs in patient 2 were due to macroprolactinemia since most of PRL eluted as big,b ig (40%) and big-PRL (45%) after gel filtration. Forty-eight percent of PRL from patient 2 was retained by the anti-hIgG column indicating the presenc e of an anti-PRL autoantibody. These data suggest that spontaneously occurr ing anti-PTH autoantibodies must be considered in the differential diagnosi s of patients with elevated serum PTH levels. (J. Endocrinol. Invest. 22: 8 29-834, 1999) (C) 1999, Editrice Kurtis.