Re: waht does abnormal quantities of chloride in urine indicate?

Dear Dany, 

first, sorry for the long delay.

Measuring the quantity of chloride in the urine is not by itself diagnostic
of any disease. The results can be indicative of several disorders when
viewed in concert with other tests. 

There are two methodologies for measuring chloride excretion. One is to
measure it from a urine sample taken from one urination (a so-called „spot
urine“), the other is to collect a whole day’s urine production in a
container and take the sample from the container after the collection
period. Results from a 24 hour urine are generally more reliable since
urine production and content varies strongly even in a healthy person on an
unremarkable day. Furthermore, you can assess the absolute amount of
excretion per day, while in a spot urine, you only get concentrations –
which are even less diagnostically valuable than absolute excretion rates. 

Daily chloride excretion is between 20 to 250 mEq (for a monovalent ion
such as chloride, this equals mmol) per day. You see from this tenfold
range that chloride excretion (and, by the way, that of any other ion) is
extremely variable even under normal conditions. 

You find increased chloride excretion in people who eat a lot of salt (NaCl
– the kidney simply does away with the unnecessary salt); in people who are
using diuretics (drugs that stimulate urine flow primarily by blocking the
recovery of salts by the kidney); and in several conditions of chronic
kidney disease in which the salt-recovering ability of the kidney is
damaged („salt-losing nephritis“). 

Also, there are some hormonal diseases which cause excessive salt, and
thus, chloride, loss by „switching“ the kidney into a salt loss mode (that
is, the kidney is healthy in itself, it just gets the wrong hormonal
signals ). One of them is a lack of glucocorticoids and mineralocorticoids
which are produced in the adrenal gland – the condition is known as
Addison’s syndrome; reputedly, former US President J. F. Kennedy suffered
from it. 

With decreased chloride excretion, you get sort of a mirror image: It is
present in people who have little or no salt intake or who loose body
fluids (all of them contain salt) via a different route: Diarrhoea, say, or
copious bleeding. This just means the kidney is saving any chloride it can
recover from the urine. Also, there are conditions which turn on the „salt
saving“ switches inside the kidney inappropriately – one such condition is
the presence of too much adrenal corticosteroids (either given as drugs or
produced by the adrenal glands).

So if you ask , „what do abnormal quantities of chloride in urine
indicate?“ the answer is a little bit disappointing, maybe: By themselves,
nothing much. Altered chloride excretion is just one consequence among many
in a large number of conditions having totally different origins and
severity. You need to view the test result (as always, in medicine) in
concert with someone’s history, physical findings, and other tests.

Greetings
Jens Peter Bork

References:  http://www.nlm.nih.gov/medlineplus/ency/article/003601.htm#visualContent
has a nice overview about how to do the actual test and urine collection.

I did not find any more easy-to-use web-based resources. Myself, I used my
battered copy of a Clinical Chemistry textbook; a large Nephrology textbook
might provide some answers, although these books tend not to go into the
peculiarities of specific tests. So probably, a clinical Chemistry textbook
will serve you best.