Corticosteroid-Binding Globulin Human ELISA

Summary

Human corticosteroid binding globulin (CBG, transcortin), also referred to as SerpinA6, belongs to the serpin superfamily. Corticosteroid binding globulin is a 52 kDa secreted α1-glycoprotein consisting of 405 amino acids. Corticosteroid binding globulin is synthesized and secreted by hepatocytes in the liver and is present in glycocorticoid responsive cells. The concentration of corticosteroid binding globulin is regulated by estrogens. CBG is the major transport protein for progestins and glucocorticoids within the blood. Thus CBG regulates their bioavailability and metabolic clearance and protects them from absorption into cells and degradation by chemicals and enzymes. CBG contains a single steroid binding site with high affinity for cortisol and progesterone. About 80–90% of circulating cortisol is bound to CBG. Albumin bound cortisol is reported to represent 14% and free cortisol 6% of total plasma cortisol under basal conditions. The CBG bound cortisol is considered to be biologically inactive, whereas the unbound cortisol constitutes the active form of cortisol. The active fraction of plasma cortisol will thus depend on the concentration of CBG. Defects in the gene encoding CBG are the cause of corticosteroid binding globulin deficiency (CBG deficiency), a rare disorder characterized by reduced CBG production that results in hypo/ hypertension and muscle fatigue. The plasma concentration of CBG shows little or no diurnal variation and no marked differences are observed in adult subjects according to age, sex or menstrual cycle. In umbilical cord blood, however, CBG is present at half of the normal adult level and prepubertal children have higher levels than adults. Plasma CBG levels increase during pregnancy and are decreased in cirrhosis. Estrogen therapy (e.g. feeding hormonal contraception) or implantation during pregnancy cause a very marked increase of the CBG concentration. Decreased levels of CBG are observed in women with polycystic ovary syndrome, hypoproteinemia, Cushing´s syndrome or corticoid treatment and some cases of vitamin B12 deficiency. Extremely low levels of CBG have been reported in patients with septic shock. The main clinical application of corticosteroid binding globulin measurement relates to the interpretation of cortisol levels. The concentration of unbound cortisol, which is biologically active, can be calculated from the concentration of total cortisol and that of CBG on the basis of mass action.

Features

• It is intended for research use only
• The total assay time is less than 3 hours
• The kit measures total corticosteroid binding globulin in serum and plasma (EDTA, citrate, heparin)
• Assay format is 96 wells
• Quality Controls are human serum based. No animal sera are used
• Standard is purified native protein based
• Components of the kit are provided ready to use, concentrated or lyophilized

Research topic

Immune Response, Infection and Inflammation, Steroid hormones

Assay format

Sandwich ELISA, Biotin-labelled antibody

Applications

Plasma-Citrate, Plasma-EDTA, Plasma-Heparin, Serum

Sample requirements

5 µl/well

Storage/Shipping

2 – 8°C

Calibration Curve

Calibration range

3.13 to 200 ng/ml

Limit of detection

0.01 ng/ml

Intra-assay (Within-Run, n=8)

CV = 1.7%

Inter-assay (Run-to-Run, n=5)

CV = 7.1%

Spiking Recovery

100.3%

Dilution Linearity

98.5%

Cross-Reactivity

References to this product

• Lewis JG, Bagley CJ, Elder PA, Bachmann AW, Torpy DJ. Plasma free cortisol fraction reflects levels of functioning corticosteroid-binding globulin. Clin Chim Acta. 2005 Sep;359 (1-2):189-94
• Lewis JG, Lewis MG, Elder PA. An enzyme-linked immunosorbent assay for corticosteroid-binding globulin using monoclonal and polyclonal antibodies: decline in CBG following synthetic ACTH. Clin Chim Acta. 2003 Feb;328 (1-2):121-8
• Mihrshahi R, Lewis JG, Ali SO. Hormonal effects on the secretion and glycoform profile of corticosteroid-binding globulin. J Steroid Biochem Mol Biol. 2006 Nov;101 (4-5):275-85

References to summary

• Elder PA, Lewis JG. Alternative ELISA for sex hormone-binding globulin in plasma. Clin Chem. 1998 Sep;44 (9):1999
• Lewis JG, Hunt PJ, Elder PA, Florkowski CM. Rheumatoid factor and false positive sex-hormone binding globulin. Clin Chim Acta. 2003 Jun;332 (1-2):139-41; author reply 143-4
• Murphy GP, Mittelman A, Rosenthal H, Sandberg AA. Prostatic cancer. Transcortin levels during treatment with estramustine phosphate. Urology. 1975 Jul;6 (1):17-21
• Scott RS, Elder PA, Shand BI, Lewis JG. Plasma sex hormone-binding globulin rather than corticosteroid-binding globulin is a marker of insulin resistance in obese adult males. Diabetes Obes Metab. 2004 Jul;6 (4):259-63
• Slaunwhite WR Jr, Nienhouse S, Rosenthal H, Woodruff M, Sandberg AA. Transcortin: A Corticosteroid-binding Protein of Plasma. VII. Half-Life in Normal and Estrogen-treated Subjects . J Clin Invest.. 1964 Mar; 43 :461-6;

By research topic:

• Immune Response, Infection and Inflammation
• Steroid hormones

By molecule:

• Corticosteroid-Binding Globulin

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