STIMULATED IODIDE UPTAKE IN FRTL-5 CELLS PREINCUBATED WITH GRAVES IMMUNOGLOBULINS IN NACL-FREE MEDIUM - A SENSITIVE ASSAY FOR THYROID-STIMULATING ANTIBODIES

The present study was designed to increase the sensitivity of iodide u ptake assay for detecting thyroid-stimulating antibodies (TSAb). Based on the previous observations that TSAb are more active to increase cA MP levels in the NaCl-free condition, we improved the assay procedure and defined the optimum conditions: FRTL-5 cells were incubated with i mmunoglobulin (IgG) in NaCl-free medium for 3 days, and then I-125 upt ake in the cells was determined after 60 min. The sensitivity of iodid e uptake assay for TSAb increased 3-fold by the modification, when ass essed by the IgG concentration required to elicit the same response. T he described assay is as sensitive as that using cAMP measurement in N aCl-free buffer. Thus, it could detect TSAb in all 21 patients with ac tive Graves' disease and in 7 of 8 with ophthalmic Graves' disease but not in 29 of 30 control subjects. Thyroid stimulating activities asse ssed by these two assays correlated with each other (it = 29, r = 0.70 7, p < 0.001). False positive results obtained in 4 hypothyroid patien ts with Hashimoto's thyroiditis (serum TSH concentrations, 11-171 mU/L ) could be prevented using anti-TSH antibodies. In summary, the descri bed assay allows evaluation of stimulated thyroid function directly wi thout affecting the detection of TSAb.