Endocrine function tests

Hormones

Definition: Hormones are chemical signals produced by specialized cells, secreted into the blood stream, And carried to a target tissue.

Chemical Nature:

♦ Steroids

- Steroids hormones are lipid molecules that have cholesterol as a common precursor .

- Steroids are produced by four organs: adrenal glands, ovaries, testes, and placenta.

♦ Protein - Protein hormones may be either peptides or

glycoproteins .- The peptides include insulin, glucagon, parathyroid

hormone (PTH), growth hormone (GH), and prolactin (PRL).

- The glycoprotein hormones, follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG).

♦ Amines The amines are derived from amino acids and include

epinephrine, norepinephrine, thyroxine, and triiodothyronine.

Hormone tests methodology• Bioassays

Before the development of modern assay methods, the detection and quantitation of hormones were based on expensive assays that depended on a biologic response from a live animal or tissue / organ culture.

• Competitive Protein Binding Competitive protein-binding (CPB) assays are based on competition for a limited number of protein-binding sites between a known added amount of labeled

hormone and the unlabeled hormone present in the patients sample .

• Radioimmunoassay - RIA is a CPB technique that uses radio-labeled hormone and

antibody prepared against the specific hormone as a binding site .

- Competition between unlabeled hormone in the patient sample and the added-labeled hormone for a limited number of antibody-binding sites forms the basis of the assay .

• Immunoradiometric Assay (IRMA) - IRMA is similar to RIA in that a radiolabeled substance is used

in an antibody-antigen reaction. However, the radioactive label is attached to the antibody instead of the hormone.

- IRMA = sandwich technique

form the “sandwich’’ comprising antibody- hormone –labeled antibody

The amount of hormone present is directly proportional to the amount of radioactivity measured in the assay .

• Enzyme linked Immunosorbent Assays - Enzyme linked immunosorbent assays (ELISA) have an

enzyme label

- Heterogeneous immunoassays ( Use a solid phase as the

separation technique eg : micro titer well ) - Detection method based on enzyme catalyzed reaction then

spectrophotometer is usually used to measure the color changes that are a result of enzyme activity .

• Enzyme-Multiplied Immunoassay Technique - Enzyme-Multiplied Immunoassay Technique (EMIT) have an

enzyme label

- Homogeneous assay (no physical separation of the bound and free components)