Thyroid antoantibodies and the response to thyrotropin releasing hormone in patients with subclinical hypothyroidism.

Abstract

Aim-To evaluate the clinical usefulness of the thyrotropin releasing hormone (TRH) test and estimation of thyroid autoantibody concentrations in patients with borderline raised thyroid stimulating hormone (TSH). Methods-The records of 34 consecutive patients with persistent borderline increased TSH (4.4-9.9 mU/l) referred to the Medical Investigation Unit were reviewed. MethodsThe records of 34 (30 women and four men) consecutive patients referred over an 18 month period were reviewed. The patients were aged between 23 and 80 years (58+13-9 SEM). All of the patients had borderline raised TSH concentrations (4 4-9-9 mU/l) on at least two occasions three to six months apart.Total thyroxine was measured by radioimmunoassay (Immunodiagnostic Systems Ltd, Tyne and Wear, UK); TSH was measured using a coated tube immunoradiometric assay (Immunodiagnostic Systems Ltd). Interassay precision (coefficient of variation) for the TSH assay was 7% at 3 9 mU/l and 6% at 26-5 mU/l. Thyroglobulin antibodies and thyroid microsomal antibodies were assessed by passive haemagglutination using Serodia kits (Fujirebio Inc., Tokyo, Japan). The TRH test was performed by intravenous administration of200 ,ug TRH and blood samples were collected at zero, 20 and 60 minutes.The indices used in the diagnosis of hypothyroidism were increment of TSH >30 mU/l, 20 minute TSH >35 mU/l or a proportional rise (20 minute TSH/basal TSH >6). ResultsAdministration of TRH was well tolerated by all of the patients and no side effects were reported. The mean total thyroxine concentration in the patients was 92+ 2-7 (SEM) nmol/l (range 60-112 nmol/1). Using linear regression analysis, there was good correlation between the indices used for the diagnosis of hypothyroidism (r. 0-76; p<0 001). Basal TSH alone was poorly correlated with these indices (r<0 145; p.<046)

TRH Stimulation When Basal TSH is Within the Normal Range: Is There "Sub-Biochemical" Hypothyroidism?

“…Finally, others have suggested that a ΔTSH cutoff of 25 to 30 mU/L or a 6-fold rise in TSH at 20 minutes are the cutoffs that suggest hypothyroidism. 4,11 We used a more intuitive method to arrive at our estimated cutoff of 20 mU/L and suggest this as more optimal. We do not advocate the fold-response as it varies with the basal TSH.…”