There are differences, I believe, in sensitivities when I googled it - but it is up to the doctor to pick one. Of course, it may be up to insurance as well as longer tests cost more so shorter tests cost less.
High-dose version: This dose of cosyntropin results in pharmacologic plasma ACTH concentrations for the 60-minute duration of the test, which may be too high to detect cases of chronic partial and mild pituitary ACTH deficiency (26). Therefore, this test may miss some mild cases of adrenal insufficiency. Also, in early acute secondary or tertiary adrenal insufficiency, as in Sheehan syndrome, the test is not reliable, because it takes several days for the adrenal cortex to atrophy.
A rise in serum cortisol concentration after 30 or 60 minutes to a peak of 18 to 20 µg/dL (500 to 550 nmol/L) or more is considered a normal response to high-dose ACTH stimulation test (28-30) and excludes the diagnosis of primary adrenal insufficiency and almost all cases of secondary adrenal insufficiency. However, if secondary adrenal insufficiency is of recent onset, the adrenal glands will have not yet atrophied, and will still be capable of responding to ACTH stimulation normally. In these cases, a low-dose ACTH test or an insulin-induced hypoglycemia may be required to confirm the diagnosis (31, 32).
Low-dose version: The advantage of this test is that it can detect partial adrenal insufficiency that may be missed by the standard high-dose test (31, 32). The low-dose test is also preferred in patients with secondary or tertiary adrenal insufficiency (34). The test is frought with technical problems and has not been as reliable or accurate.
Prolonged version: Prolonged stimulation with exogenous ACTH is used to differentiate between primary and secondary or tertiary adrenal insufficiency. In secondary or tertiary adrenal insufficiency, the adrenal glands display cortisol secretory capacity following prolonged stimulation with ACTH, whereas the adrenal glands in primary adrenal insufficiency are partially or completely destroyed and do not respond to ACTH.
Two-day version: This test may be helpful in distinguishing primary from secondary/tertiary adrenal insufficiency. In primary adrenal insufficiency there is no or a minimal response of plasma or urinary cortisol and urinary 17-OHCS. Increases of these values in the 2-3 days of the test are indicative of a secondary/tertiary cause of adrenal insufficiency.
Cortisol: Serum cortisol concentrations determined at 08:00h of less than 3 µg/dL (80 nmol/L) are strongly suggestive of adrenal insufficiency (25), while values below 10 µg/dL (275 nmol/L) make the diagnosis likely. Basal urinary cortisol and 17-hydroxycorticosteroid excretion is low in patients with severe adrenal insufficiency, but may be low-normal in patients with partial adrenal insufficiency. Generally, baseline urinary measurements are not recommended for the diagnosis of adrenal insufficiency.
This test can be given as a low dose short test (1 microgram of Cortrosyn or Synacthen) (ie short Synacthen test) or conventional dose short test (250 micrograms). Studies have shown there is no significant difference between the low dose and conventional dose of Cortrosyn or Synacthen in the measured stress response of the adrenals.
Prolonged stimulation with exogenous ACTH is used to differentiate between primary and secondary or tertiary adrenal insufficiency, but is rarely given (as a long conventional dose test which can last up to 48 hours) because earlier testing of cortisol and ACTH levels in association with the short test may provide all necessary information.
The ACTH stimulation test is recognized by the medical community as the final say in whether or not an individual has a degree of adrenal insufficiency, although this test is primarily used to determine the presence of Addison's disease and pituitary impairment.
Currently, the most popular test for adrenal insufficiency is the conventional rapid ACTH stimulation test (250 µg ACTH). This method is quick and safe, but incorporates a dose of ACTH that is supraphysiological and capable of transiently stimulating the adrenal cortex in many patients with documented central adrenal insufficiency. In recent years, several investigators have published substantial evidence for a more sensitive ACTH stimulation test using a lower dose of ACTH (1 µg). Further analysis of these data, including the calculation of likelihood ratios, demonstrates that the 1-µg test performs significantly better than the 250-µg test compared to the gold standard, insulin tolerance test. We suggest that the 1-µg ACTH stimulation test replace the conventional 250-µg test when evaluating for central adrenal insufficiency. A cortisol level below 500 nmol/L after 30 min signifies impaired adrenocortical reserve. An insulin tolerance test should be performed if this low dose test results in a borderline value and the diagnosis is questioned. The 1-µg test should not be used if recent pituitary injury is suspected. Pharmaceutical companies should be encouraged to provide synthetic ACTH in 1-µg vials.
I also read from a lab that there are different time version of this test. Such as:
baseline and 60 min;
baseline, 30min, 60min;
baseline, 15min, 30min, 60min.
I read from a lab that the lab doesn't supply the Cortrosyn that they inject you with. So would I need to get a prescription and pick it up from the pharmacy? Is it hard for pharmacies to get? How long would it last in my refrigerator? What dose does my doctor have to prescribe?
When I checked, a lot of research papers said the theoretical sensitivity of the low dose ACTH test was admirable and maybe even makes it a superior test to the normal 250 mcg test.
But, in Boston, where there's oodles of hospitals, I asked an endo this week about it and she said she didn't really know of anyone using that test around here.
Remember that what is on the radar of researchers may take 5-10 years to filter down to your local clinic. And all humans resist change, even MDs.
The company that makes Cortrosyn (one of the brand names of the drug used) has little incentive to pre-package doses that are '250 times less ingredients than before'.....after all, how much extra can they charge for the extra cost of repackaging the stuff? Most everyone will assume the price will be lower, not higher. But in fact, sometimes the real cost of these drugs is more the box it comes in than the active ingredient....Try explaining that to the public and getting 'buy in'...!
So I'm betting that the low dose will remain a good theory for a while until medical politics maybe moves it into the mainstream. Could take years.
Or a Hollywood celebrity recommends it on a morning talk show. In which caset it could be everywhere by Christmas.
I talked to my hospital lab about the low-dose ACTH Stimulation Test, then was told to talk to the IV Nurse, which got directed to the hospital pharmacy. They pulled up the diluting directions from the subscription form of the UpToDate website. They said they can do the test, and that I'd need to talk to the lab about how my doctor should write it out on the lab sheet.
It's more sensitive than the regular dose, so I'm going for it.
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