Several Test Involved in the Hormones Secreted by the Adrenal Cortex
After the release of my 1st post here about the adrenal cortex and its hormones, I'm sure you've been so pretty curious a lot about how can we relate this to what we examine always here in Clinical Chemistry, which is serum.
Now, in this post, you will find some pretty cool information, on how they are tested and at the same time to be related to what particular disease your mom, your neighbor, your cousin, your friend, your community, your fellow citizen or you might be having.. Just kidding!!ahaha!!
But before we go to anything else and dig deeper with the test involved in our precious adrenal cortex, let's take a brief recall on some basic principle on our serology subject, that will help us be more understand the principle underlying this test.
Let's review what we have learned about the principle of the RIA or Radioimmunoassay.
As we commonly know, RIA makes use of radioactive isotopes in the test.
Then this isotopes will be coated to the hormone to be assayed. Then it will be allowed to chemically react to the antibody which is specific against it.
Then, a patient serum is added to the reaction. Hence, the patient serum will tend to battle against the hot antigen( antigen that first combined) for partnership with the antibody. As this reaction continues to precede, presence of free bound antigen become to be supernatant. And this is the one being measured for the antigen.
A portray below is given for easier understanding:
photo from:
After knowing the basics, now let's go to the real subject matter.
ACTH Test (RIA)
It is primarily a test using a radioactive substance to acts a hot antigen, the antibody specific for ACTH, and the patient's serum. As shown in the above principle, it is measured indirectly by measuring the unbound or free antigens that became supernatant.
Now can you ask yourself. Is it easy or not?
Above this convenience in testing, there are some precautions as well as limitation in assessing the ACTH in the serum
Precautions of the Test
1. Refrigerate at 4 degrees Celsius if not to be processed immediately.
2. It should not be held in contact upon processing, because it will cling collectively to the glass.
3. Damage using incubation period
Limitations or Disadvantage of the Test:
1. ACTH in the plasma are easily degraded - in the presence of proteolytic enzymes
2. ACTH depends on Circadian Rhythm
3. ACTH have decrease concentration in the serum
4. It is quite expensive
Normal Values
Healthy persons = <>
Dexamethasone Suppression Test for ACTH
A test for ACTH that makes use of dexamethasone an artificially produced glucocorticoid that counteracts the release of ACTH without affecting the urine output. Thereby, fall down of the value of the cortisol concentration in the plasma is the normal reaction is expected.
A low-intake of dexamethasone and a high-intake if needed is introduced to a patient that is tested for possible Cushing syndrome.
Clinical Significance of the result:
A patient who has undergone this test who has a result of a not decreased cortisol, but an elevated ACTH is correlated with ectopic ACTH syndrome.
On the other hand, a patient result of a non-drecreased cortisol, and a non-decreased ACTH is correlated with an adrenal tumor .
ACTH Stimulation Test
In this test, a ACTH is injected intravasularly and cortisol level will tend to elevate after an hour of injection. This phenomenon happen for a normal person. On the other hand, hypodrenalism is possible for a person who has not increased in cortisol levels or other hormonal products. That's why it is a good screening test for hypoadrenalism.
Metapyrone-ACTH Stimulation Test
It is also an ACTH stimulation test, but other than we inject ACTH, metapyrone a drug taken orally is ingested. In this case, metpyrone stops the production of cortisol by means of blocking they function of enzyme 11B-hydroxylase.
Now let's go to the hormones that is produced primarily by the adrenal cortex. And the first one is the cortisol.
Cortisol: Fluorometric Assay
The mechanism behind this assay is that cortisol is measured via fluorescence. How this may be possible? Serum is added with dichloromethane which was acidified using acid alcohol solution. Then the fluoresce that will be produced will be measured.
Limitations and Precautions
1. Test somewhat become innacurate because of the presence of interferring substances like corticosterone and other adrenal steroids.
2.Other medication also like tetracycline, spironolactone, and other medicines that raise up the level of cortisol is considered as interferring substances which will lead to false positive results
Cortisol: Competitive Binding Protein Test
A test in which makes use of the transcortin, a naturally occuring cortisol binding protein from some species. This transcotin bind with the cortisol and then are measured.
The thing that makes this method an important one is that it enables separation of 11- deoxycortisol, an interferring substance with carbon tetrachloride. Eliminating the interferring substances procedes as now in the measuring and reading process.
Cortisol: RIA
If you recall, what we have discussed before proceeding to the test, you can easily understand the concept of the this test. In this test, cortisol is separated form its binding protein by making use of inhibiting agents such as 8-anilino-1-naphthalene sulfonic acid.
Then this free cortisol that became supernatant is measured.
Cortisol: HPLC( High Performance Liquid Chromtography) Assay
Above all test, this one is the most dominant in specificity. In this test, we makes use of a reverse-phase liquid chromatography with an ultraviolet detector. The principle behind this is the movement of the mobile phase from one point to another, while the stationary phase remains in its place.
The advantage of this method is that it is not being limited by interferring substances that may tend to yield false positive or false negative result. With the automation included, simultaneous test can be done also for other steroid hormones.
Normal Values of Serum Cortisol
50-250 ug/L at 0800 to 1000 hours then drops at 20 to 120 ug/L by 2000 hours
From Clinical Laboratory Diagnosis and Management by Laboratory Methods
References:
Clinical Diagnosis and Management by Laboratory Methods 20th Ed. by Bernard, John Henry
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