Hormonal immunoassay studies of thyroid function in healthy adults and pregnant subjects in Dar-es-Salaam, Tanzania.

Abstract

Public health problem in many parts of the world, including Tanzania. The consequences of iodine deficiency include thyroid dysfunction abnormalities, endemic goitre and cretinism, endemic mental retardation, decreased fertility rate, increased perinatal death and infant mortality. Assays of

thyroid hormones and thyrotropin are essential for the diagnosis and treatment of 100. Until now, the Department of Clinical Biochemistry at the Muhimbili Medical Centre, Dar-es-Salaam has no thyroidology service. # This study was undertaken to evaluate thyroid function in healthy pregnant and non- pregnant Tanzanian subjects from iodine replete areas in order to establish baseline information for projected studies on effects of 100 on human reproduction. Furthermore the analytical performance of Serozyme immunoassays for the measurement of T4' T3' TSH and T3Uptake as a possible basis for a future thyroidology service were evaluated. This system was proposed on the basis of pilot studies comparing the results of Serozyme assays and the methods routinely used in the Laboratory for Endocrinology and Reproduction, Academic Hospital Nijmegen, St Radboud, The Netherlands. Moreover Serozyme assays are relatively easy to perform and require inexpensive instrumentation which is easy to operate. Serum was obtained from clinically euthyroid pregnant and non- pregnant adult subjects living in Dar-es-Salaam, Tanzania. Results from the analysis of these samples using routine assays confirmed to a large extent that levels of thyroid hormones and thyrotropin were comparable to those published for other euthyroid populations, except that Tanzanian males had higher T31evels than females and Tanzanian adults had higher T4 and T31evels than Dutch ~ ------- ---~----- ------- - - -~-

-- - ---~-- --- ii adults. Thyroid function in clinically euthyroid pregnant Tanzanian women was also found to be in accordance with findings from similar studies. Assessed by free T4 and TSH levels almost all (99%) of pregnant Tanzanian women were found to maintain euthyroidism. Serozyme assays for T4' T3 and TSH generally showed a reasonable agreement with routine assays. Yet, the precision of the Serozyme T4 assay was not satisfactory. Moreover it was noted that in a relatively large proportion of the Tanzanian samples (about 20%) the Serozyme T3 assay failed to detect T3 whereas it was detectable by Amersham T3 RIA. Also, levels assessed using the Serozyme TSH assay were spuriously elevated in about 20% of the samples. It is suggested that heterophilic antibodies present in the serum of Tanzanian subjects may cause this interference. In this study, several approaches were investigated to circumvent this interference. Serozyme T3 Uptake did not distinguish between pregnant and non- pregnant groups, so that Serozyme free T4 index did not reflect - the euthyroid status of normal pregnancy: about half of the subjects had their free thyroxine index falling within the non-pregnant range. It is concluded that, although initially Serozyme assays seemed to have many advantages, they are not the preferential choice for the introduction of diagnostic services in Tanzania unless measures can be taken to prevent interference. It is recommended that further studies should be done to conclusively identify the interferant in the T3 and TSH assays. Taking into account the costs and poor analytical perfonnance-ofthe Serozyme kits, the possibilities of developing in-house immunoassays which can be run on the Serozyme 1 analyzer should be explored.