Changes in circulating thyroid hormone levels and systolic time intervals in acute hypothyroidism

Acute changes in clinical parameters and thyroid function peripheral markers following L-T4 withdrawal in patients totally thyroidectomized for thyroid cancer

After total thyroidectomy, differentiated thyroid cancer (DTC) patients have to undergo L-T4 withdrawal for measuring serum thyroglobulin and 131I whole-body scan (131I WBS) to evaluate residual/recurrent malignant disease. The aim of the present work was to study in these patients the effects of acute thyroid hormone deficiency on various target organs and tissues. Clinical parameters and thyroid function peripheral markers were evaluated in 20 DTC patients, both before and after L-T4 withdrawal. A 24-h urine collection, a fasting blood sample for laboratory examinations, a clinical score for hypothyroidism and cardiovascular, neurological and neuropsychological evaluations were carried out. After L-T4 withdrawal, the clinical score significantly increased, as well as total cholesterol, triglycerides, creatine kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase, whereas SHBG, osteocalcin and urine hydroxyproline levels significantly decreased. The acute thyroid hormone deficiency caused a systolic dysfunction of the left ventricle associated with an increase in systemic vascular resistance without cardiac contractility alterations. A significant increase in the left ventricular mass and thickness was also observed. Carpal tunnel syndrome appeared in 30% of patients and a significant reduction in the immediate auditive memorization and in attentive performance was also detected. These observations indicate that acute hypothyroidism causes significant clinical alterations of peripheral tissue function. In the follow-up of DTC patients, therefore, L-T4 withdrawal procedure should be restricted to cases where the cost/benefit ratio is favorable. Alternative procedures, such as the use of recombinant human TSH, should be used whenever possible.

Thyroid stimulating hormone measurement using a third generation immunometric assay

After an initial evaluation of the standard procedure for performance of a third generation TSH (thyroid stimulating hormone) assay (Amerlite TSH-30) modifications were made to standardize the timing of measurement of light emission following signal reagent addition. By adopting this optimized procedure, a significant improvement in assay sensitivity was achieved when compared to a second generation TSH assay (DAKO). Using the optimized assay the sensitivity was 0.003 mU/L (20 replicates of zero) or 0.009 mU/L [22% CV (coefficient of variation) from the precision profile]. Recovery of added TSH and parallelism of the assay were good. A significant negative bias was detected for the Amerlite TSH-30 assay when compared to the DAKO assay (log y = 0.92 log x-0.33, n = 210). Excellent discrimination was achieved between euthyroid, hypothyroid and thyrotoxic subjects. A high percentage of thyrotoxic patients had undetectable TSH and the spread of values between thyrotoxic and euthyroid was greater with the third generation assay. In patients receiving thyroxine therapy a higher percentage had detectable TSH values. The optimized Amerlite TSH 30 assay offers improved assay performance when compared to a second generation assay.