|MadSci Network: Medicine|
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.
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