4
$\begingroup$

Are the levels of antidiuretic hormone in the plasma somehow hard to measure or are the results unreliable, and if so why?

Some countries have moved away from testing for ADH (the national health care systems no longer cover the test so one has to pay out of pocket) saying that it is no longer used either way in medical practice (i.e the test is obsolete).

I wonder whether water deprivation and desmopressin stimulation testing are actually alternatives or why not simply use all three tests. Water deprivation and desmopressin stimulation seem to me less appropriate since one seems to be "cruel and unusual punishment" and the other requires the intake of a substance.

In the National Library of Medicine I have searched for Diabetes Insipidus, Antidiuretic Hormone, Arginine Vasopressin. But at most I could find that the half-life is short (still twice as much as those of the hypothalamic releasing or inhibiting hormones).

Diagnosis and Management of Central Diabetes Insipidus in Adults

Physiology of antidiuretic hormone and the interrelationship between the hormone and the kidney

Above are a couple of papers I read in my search. It seems strange not to test for ADH since it is so central in Central diabetes insipidus (can't understand how the "alternatives" may be more appropriate, more cost effective or have higher diagnostic value).

$\endgroup$

1 Answer 1

0
$\begingroup$

ADH is highly unstable. This is why it is better to test for copeptin which is much more stable and correlates well with ADH. This is also written in the first article which you linked.

The other problem is that neither copeptin nor ADH levels won't neccessarily give you a definite diagnosis. If a patient has complete arginine-vasopressin deficiency, then ADH/copeptin will be so low that you will be able to diagnose central DI based only on those values and serum/urine osmolality. But if a patient has partial arginine vasopressin deficiency, you have multiple problems. First of all, the levels of ADH/copeptin are highly dependent on fluid intake, so you need controlled environment in order to get relevant measurments. Second of all, a patient might have equivocal results which don't yield a definite diagnosis - for example polyuria with polydipsia and with low normal copeptin, low urine osmolality, normal serum osmolality, normal electrolytes. These results do point towards central DI but you can't be certain. This is why you need the functional tests which may give you new information (though it's not neccessary that they will give you any new information - they might turn out equivocal as well).

Long story short - measuring copeptin is definitely sensible because it can sometimes diagnose central DI on itself. But functional tests are commonly neccessary because they are the only currently known way to formally test the maximum urine concentration a patient can achieve which is an important piece of information when previous results are equivocal.

$\endgroup$
5
  • $\begingroup$ Considering the question was tagged with biochemistry and proteins (I explicitly included the how so in the question) can you explain why (how) ADH is highly unstable? $\endgroup$ Commented Apr 16 at 19:30
  • 2
    $\begingroup$ I cannot because I sadly don't know why ADH is unstable. I thought the question "how so" was regarded to the reliability of the test and not to the stability of ADH. $\endgroup$ Commented Apr 16 at 19:56
  • $\begingroup$ @GeorgeNtoulos — Read the question, not the tags. Anyway I have edited it and removed the protein tag. The question is about why a method has been discontinued, not about anything distal to that. The question would have been better posted on Medical Sciences anyway. $\endgroup$
    – David
    Commented May 16 at 20:57
  • $\begingroup$ @David I think the stability of ADH (and other things that have to do with the protein in itself like the method to measure, the secretion) is crucial to the question. I am not negative to a migration to Megical Sciences. If the community finds the question to better fit there I am all for it. $\endgroup$ Commented May 16 at 22:32
  • $\begingroup$ @GeorgeNtoulos — No. we only allow one question at a time. Your question is why a particular assay has been discontinued — a medical question. If this answer is correct and the reason is the instability of ADH, then a quite distinct question is “why is ADH unstable, from a biochemical standpoint?” But you would have to do some homework on that topic before asking that separately. $\endgroup$
    – David
    Commented May 17 at 14:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .