clinchem blog notes 30 b LAB LETTERS: URINARY CORTISOL TEST

URINARY CORTISOL TEST

Posted by clinical chemistry blog notes 31-10 ,

Ever heard of those small triangular glands sitting on top of your kidneys? They are called the adrenal glands and they are responsible for manufacturing a steroid called CORTISOL. Cortisol’s main function is to enhance glucose production, working oppositely with that of insulin.

Because the pituitary gland releases the adrenocorticotrophic hormone (ACTH) to stimulate the production of hormone, high levels of it may make the adrenal glands work over time to make cortisol. Sometimes excess cortisol is produced by adrenal gland tumors. Exogenous administration of glucocorticoids may also cause cortisol to rise dramatically.

And its effect? I bet you wouldn’t like it. Some physical manifestations of increased cortisol levels (hypercortisolism) would include rapid gain weight, growth of a “buffalo hump”, hirsutism and baldness. This is collectively known as the Cushing’s syndrome.

Like all other diseases, tests should be done in order to accurately diagnose Cushing’s syndrome. One of which is the Urinary Cortisol Test. When serum cortisol exceeds the capacity of carrier binding proteins, free or unbound cortisol rise dramatically. The free cortisol is then filtered in the urine. The level of free cortisol in the urine can then be measured.

A 24-hr urine collection is the specimen of choice for Urinary Cortisol Test. To see the preparation of 24-hr urine specimen click HERE.

The Urinary Free-Cortisol Excretion (UFC) is the desired test for the measurement of free cortisol. It directly measures its concentration in the urine. Cortisol is extracted from the urine sample and then followed by radioimmunoassay (RIA).

To perform radioimmunoassay, a known quantity of an antigen is made radioactive. This radiolabeled antigen is then mixed with a known amount of antibody for that antigen, and as a result, the two chemically bind to one another. Then, a urine sample from a patient containing an unknown quantity of that same antigen (cortisol) is added. This causes the unlabeled cortisol antigen from the urine to compete with the radiolabeled antigen for antibody binding sites. The bound antigens are then separated from the unbound ones, and the radioactivity of the free antigen remaining in the supernatant is measured.

Uuuuuhhhhh… Still bothers your mind? Check this out.

The normal average excretion of urinary free-cortisol is less than 100ug/day.

Another test that can be used is the Porter-Silber Reaction. It is also termed as the 17-hydroxycortecosteroid Test. The dihydroxyacetone side chain of the steroid reacts with 2,4-dinitrophenylhydrazine to form a yellow derivative. It is measured spectrophotometrically at a maximum absorbance of 410nm.

To simplify it, here’s the formula:

17,21-Dihydroxy-20-ketone + 2,4-Dinitro-phenylhydrazine ---------> Yellow pigment

The normal range for Porter-Silber chromogens is 2.5 -6.5/g creatinine per day.

Is there anything else I should know?

The values for the UFC may increase if there is increased urine output. Patients who drink more than 5L/day will have a 64% in urine cortisol.

Porter-Silber Reaction is not affected by volume changes.

Determination of plasma cortisol level is also available.

In order to confirm hypercortisolism, three times of test is need with significant results

Cortisol concentration in the blood may vary throughout the day. At 8 a.m., the normal cortisol level ranges from 7 to 22 ng/dl when measured by radioimmunoassay. This value is twice the level that is expected when the test is performed on plasma obtained at 8 p.m.

Pregnancy may cause cortisol level to increase.

Clinchem30b FACT #2 (nice to know):

Cortisol blockers are said to help lessen fat accumulation because cortisol permits the production of glucose. What they don't say is that the connection between stress hormones and weight gain is still a theory. There's no evidence that blocking cortisol results in weight loss.

In 2007, the Federal Trade Commission charged the marketers of Cortisol blockers with making false about their products' effectiveness for weight loss. The companies were forced to pay millions of dollars in refunds and to stop making unproven claims about their products.

from: http://www.mayoclinic.com/health/cortisol-blockers/an01275

Well that’s about it. I hope its informative enough for you guys!

References:

M. Bishop; Clinical Chemistry: Principles, Procedures, Correlations
D. Calbreath; Clinical Chemistry: A Fundamental Textbook

http://books.google.com/books?id=a-Eg0vPb6o4C&pg=PA134&dq=urinary+cortisol+test&cd=3#v=onepage&q=urinary%20cortisol%20test&f=false

http://books.google.com/books?id=FVfzRvaucq8C&pg=PA719&dq=urinary+free+cortisol&cd=2#v=onepage&q=urinary%20free%20cortisol&f=false