Measurement of serum PDN-21 (Katacalcin) levels by radioimmunoassay in patients with various thyroid diseases.

We established a radioimmunoassay (RIA) using anti-PDN-21 antiserum, which was obtained by immunizing rabbits with synthesized PDN-21, and the basic results are described in this report, with discussion of the significance of PDN-21 determination in various thyroid diseases. In this RIA, the double antibody technique was used for B/F separation. This assay yielded excellent standard curves, specificity, recovery and reproducibility showing that the assay is satisfactory from the clinical standpoint. The upper limit of the normal PDN-21 level was 67 pg/ml in 98 healthy persons. Only patients with medullary carcinoma of the thyroid among patients with various thyroid diseases showed specifically positive assay results. The level was 110 to 18,300 pg/ml (mean, 5,940 pg/ml) in 7 patients whose levels were determined preoperatively, and 64 to 140,000 pg/ml (mean, 10,900 pg/ml) in 18 patients whose levels were determined postoperatively. Thus, PDN-21 levels increased very sharply in the settings of recurrence and tumor residue. These results suggest that PDN-21 has the potential to be an extremely sensitive, highly specific marker for medullary carcinoma of the thyroid.