INTENDED USE

This Human TSH ELISA Kit is to be used for the in vitro quantitative determination of human thyroid stimulating hormone (TSH) concentrations in serum. This kit is intended LABORATORY FOR RESEARCH USE ONLY and is not for use in diagnostic or therapeutic procedures.

INTRODUCTION

The determination of serum or plasma levels of thyroid-stimulating hormone (TSH, or thyrotropin) is recognized as a sensitive method in the diagnosis of primary and secondary hypothyroidism. Thyroid-stimulating hormone is secreted by the anterior lobe of the pituitary gland and induces the production and release of thyroxine and triiodothyronine from the thyroid gland. It is glycoprotein with a molecular weight of approximately 28,000 Daltons, consisting of two chemically different subunits, alpha and beta.

Although the concentration of TSH in the blood is extremely low, it is essential for the maintenance of normal thyroid function. The release of TSH is regulated by a TSH-releasing hormone (TRH) produced by the hypothalamus. The levels of TSH and TRH are inversely related to the level of thyroid hormone. When there is a high level of thyroid hormone in the blood, less TRH is released by the hypothalamus, so the pituitary secretes less TSH. The opposite action will occur when there is decreased thyroid hormone in the blood. This process is known as a negative feedback mechanism and is responsible for maintaining the proper blood levels of these hormones.

TSH and the pituitary glycoproteins: luteinizing hormone (LH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) have identical alpha chains. The beta chain is distinct but does contain identical amino acid sequences, which can cause considerable cross-reactivity with some polyclonal TSH antisera. The use of monoclonal antibodies in this Human TSH ELISA Kit eliminates this interference, which could result in falsely elevated TSH values in either menopausal or pregnant females, a population whose evaluation of thyroid status is clinically significant.

PRINCIPLE OF THE ASSAY

This TSH enzyme linked immunosorbent assay (ELISA) applies a technique called a quantitative sandwich immunoassay. The microtiter plate provided in this kit has been pre-coated with a monoclonal antibody specific for TSH. Standards or samples are then added to the microtiter plate wells and TSH if present, will bind to the antibody pre-coated wells. In order to quantitatively determine the amount of TSH present in the sample, a standardized preparation of horseradish peroxidase (HRP)-conjugated monoclonal antibody, specific for TSH are added to each well to “sandwich” the TSH immobilized on the plate. The microtiter plate undergoes incubation, and then the wells are thoroughly washed to remove all unbound components. Next, a TMB (3,3",5,5" tetramethyl-benzidine) substrate solution is added to each well. The enzyme (HRP) and substrate are allowed to react over a short incubation period. Only those wells that contain TSH and enzyme-conjugated antibody will exhibit a change in colour. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the colour change is measured spectrophotometrically at a wavelength of 450 nm.

In order to measure the concentration of TSH in the sample, this Human TSH ELISA Kit includes a set of calibration standards (6 standards). The calibration standards are assayed at the same time as the samples and allow the operator to produce a standard curve of Optical Density (O.D.) versus TSH concentration (mIU/mL). The concentration of TSH in the samples is then determined by comparing the O.D. of the samples to the standard curve.

CITATIONS

1. Q Xu, X Yuan et al. Isolation of tumour stem-like cells from benign tumours. Br J Cancer. Jul 21, 2009; 101(2): 303–311.