TSH (neonatal) ELISA
The Neonatal hTSH ELISA kit is specifically designed to quantitate human thyroid stimulating hormone from neonatal blood spot samples collected on Schleicher and Schuell’s filter paper.
Clinical Physiology
Thyroid stimulating hormone (TSH) is responsible for providing the primary stimulus for the synthesis and secretion of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). This glycoprotein hormone is secreted by the anterior pituitary, under the control of thyrotropin releasing factor (TRH), produced in the hypothalamus. The thyroid hormones produced under the direction of TSH exert a negative feedback on the pituitary, which regulates secretion of TSH. (1)
Clinical Applications
As a result of the negative feedback relationship between the thyroid and pituitary glands, TSH is always elevated in primary hypothyroidism, often to very high levels. It is therefore the most sensitive test of hypothyroidism, including patients whose T4 values are still within the normal range. (1,2) Primary congenital hypothyroidism, caused by athyroidism and hypoplasia, occurs in 1 out of every 3,000 to 7,000 infants. (3) It is probably one of the most preventable causes of mental retardation. Studies have shown that the early clinical diagnosis and subsequent treatment of this disorder, usually within the first month after birth, tends to prevent irreversible mental retardation. (4,5) Recent data suggests that the most effective method of assessing the infant’s thyroid function is a combination of a T4 and TSH screening program. (4,5,6) This is due to the fact that some TSH screenings may miss hypothyroidism of the secondary type, while some T4 determinations may miss minimal hyperthyroidism. Therefore, the combination of T4 and TSH affords the clinician with the best possible overview of the infant’s thyroid state. Infants suspected of marginal or borderline hypothyroidism by virtue of the blood spot screening procedures should have confirmation test, performed by using serum T3, T4, and TSH determinations as well as other thyroid tests prior to initiating therapy. Concentrations of TSH and T4 have been shown to vary due to demographic variations, infant age, weight, and prematurity. Therefore, it is important that each laboratory determine its own normals and cutoffs with infant age taken into account.
The Neonatal TSH ELISA kit employs an enzyme-linked immunosorbent assay (ELISA) technique to quantitate Human Thyroid Stimulating Hormone in a blood spot sample. In ELISA assays, two complementary antibody configurations are generated against different portions of the same antigen. In the Neonatal TSH ELISA kit, one antibody is bound to the microwell and the other antibody is labeled with an enzyme. When an antigen is present, it simultaneously binds both antibodies in a „bridge“ or „sandwich“ fashion. This entire complex remains bound to the well. After washing out “unbound” enzyme, a specific substrate is added and converted to a colored and-product and the reaction is rapidly terminated with stopping solution. The absorbance is read for each well at 450 nm and the results plotted as concentration of TSH in IU/ml vs Abs. on graph paper. In our procedure, a disk is punched from a blood spot collected on Schleicher and Schuell’s filter paper #903. This disk is placed into the antibody well along with an eluting buffer. After overnight incubation, the eluting buffer and blood spot are aspirated out, the well washed and enzyme-labeled antibody added. After a second incubation, the well is washed and substrate is added. The enzyme reaction is rapidly terminated with stopping solution and the absorbance read. A standard curve is then constructed from which unknown concentrations of TSH can be calculated.
- Spaulding, S. W. and R. D. Utiger: The thyroid: Physiololgy, hyperthyroidism, hopothyroidism, and the painful thyroid. In Endocrinology and Metabolism. P. Felig et.al. (Ed.) McGraw Hill, 1981.
- Kapein, E.M. et.al. Thyroxine metabolism in the low thyroxine state of critical nonthyroidal illness. J. Endocrinol. Metab. 53: 764-71, 1981.
- Committe of the American Thyroid Association, Recommendations for congential Hypothyroidism. M. Pediatr. 89: 692-692, 1976.
- Fisher, D.A. Neonatal Thyroid Screening, Pediatric Clinics of North America, 25:423-430, 1978.
- Dussalt, J. H., et al.: Preliminary report on a mass screening program for neonatal hypothyroidism. J. Pediatr. 86: 670-674, 1975.
- Fisher, D.A., Pediatric Aspects. The Thyroid, 4th Edition, S.C. Werner, et.al. (Eds) Harper and Row, Hagerstown, p. 947, 1978.
- Fisher, D.A. et.al. Screening for congenital hypothyroidism: Results of screening one million North American Infants. J. Pediatr. 94: 700-705, 1979.
- Travis, J.C. et.al. Methods of Quality Control and Clinical Evaluation of a Commercial Thyroxine and Thyrotropin Assay for Use in Neonates. Clinical Chemistry 25: 735-740, 1979.
- Travis, J.C., Fundamentals of RIA and other Ligand Assays, Scientific Newsletters, Inc., Anaheim, 1979.