# How does urinalysis work? (Variable dilution issue) **URL:** \ **Category:** Factual Questions\ **Created:** [March 16, 2026, 8:37pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502 "2026-03-16T20:37:20Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [March 17, 2026, 1:50am UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/21 "2026-03-17T01:50:41Z")
I just meant hydration. Referring to a sugary drink was confusing, sorry. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [March 17, 2026, 2:23am UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/22 "2026-03-17T02:23:59Z")
> [@Beckdawrek](#): > > I don’t have kidneys. You think highly trained medical professionals would know since I don’t have kidneys, I wouldn’t have pee. A housemate in college was doing his medical school work, mentioned a situation in a hospital when someone had a kidney removed. The doctor the next day asked how she was feeling, and she said ”Oh, much better than when I had the other one removed 10 years ago.” Panic flipping through the medical charts, then quickly arranging for dialysis. Back in the days when all records were on paper… ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [March 17, 2026, 10:14am UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/23 "2026-03-17T10:14:13Z")
It’s not quite the same thing but for wastewater analysis (of e.g. drugs or ‘rona), researchers will normalize against bio markers like creatinine or viral fecal markers to account for different dilutions. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [March 17, 2026, 2:25pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/24 "2026-03-17T14:25:59Z")
Interesting. Sounds like you got more than the FAA minimum. I used to use the same person for my PCP & my FAA, and we were careful to distinguish which info was for which purpose. ---
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [March 17, 2026, 2:30pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/25 "2026-03-17T14:30:25Z")
I can’t for the life of me remember what it was for (possibly when I was first diagnosed with Type 2 diabetes) but I had a urine test that was take-home and they specified that I had to do it first thing in the morning when I got up. I’ve had to do it first thing for my dogs too (looking for kidney function, not a UTI). Now I have to do a yearly urine albumin-to-creatinine ratio test and they don’t have any stipulations as to when it’s done. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [March 17, 2026, 3:52pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/26 "2026-03-17T15:52:11Z")
Urine tests should be done periodically, certainly every year or two. Urine drug screens are a different test, where they look for metabolites of common drugs of abuse. (e.g. Cocaine is metabolized to benzolecgonine detectable for days). The standard routine test uses chemicals that turn different colours in response to varying levels of protein, glucose, pH, specific density, blood, white blood cells and leukocyte esterase as possible markers of infection, Dilute samples would have changed in pH and abnormal specific gravity. Microscopy is also often done to identify other casts and cells which correlate to specific problems and increase the accuracy of diagnosis. Cultures are done when infection is suspected to confirm things and help direct treatment. ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [March 17, 2026, 5:14pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/27 "2026-03-17T17:14:55Z")
I have had moderate kidney issues for decades, so I get a urinalysis regularly. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [March 17, 2026, 5:47pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/28 "2026-03-17T17:47:47Z")
Yeah my last urinalysis was about 15 years ago, I’m guessing, when I first went to this PCP. He hasn’t given me one since and I go annually to all my checkups. Never missed one. All my bloodwork like basic metabolic panel and lipids are good, so maybe I don’t need to. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [March 17, 2026, 6:12pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/29 "2026-03-17T18:12:05Z")
> [@Ruken](#): > > researchers will normalize against bio markers like creatinine or viral fecal markers Thanks, having wondered myself. I think this must closer to the techniques used. ---
**Author:** ![phs3](https://avatars.discourse-cdn.com/v4/letter/p/8491ac/32.png) [@phs3](https://boards.straightdope.com/u/phs3)\ **Post date:** [March 17, 2026, 7:05pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/30 "2026-03-17T19:05:15Z")
> [@LSLGuy](#): > > …they have a little chemically treated test strip they dip in the urine which turns color if the urine has sugar in it. Which beats how they did it 100 years ago: they had specially trained people who would TASTE the urine and rule based on how sweet it was. Now there’s a job that probably nobody is sorry technology has replaced! ---
**Author:** ![Vlad\_Igor](https://avatars.discourse-cdn.com/v4/letter/v/7feea3/32.png) [@Vlad\_Igor](https://boards.straightdope.com/u/Vlad_Igor)\ **Post date:** [March 17, 2026, 8:58pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/31 "2026-03-17T20:58:34Z")
As you have read up- (or down- ) thread, there are two ways to measure things in urine. One is the dipstick, which measures absolute presence, absence, or semi-quantitative mass of various substances that can indicate something to be addressed. Those measures can vary based on the concentration of the sample, so the specific gravity needs to be taken into account. The other is a relative measure of something, say, glucose _relative_ to creatinine. Creatinine is cleared from blood by the kidneys at a fairly constant rate, so measuring a substance relative to creatinine solves the problem of the variation in urine concentration (i.e., the specific gravity). So, a dipstick urine analysis may show glucose at 0-15 mg/dL, but a relative measure of the same sample from a chemistry analyzer might be 23 mg glucose/[1] mg creatinine. Vlad/Igor, MT(ASCP) ---
**Author:** ![Noelq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/noelq/32/16438_2.png) [@Noelq](https://boards.straightdope.com/u/Noelq)\ **Post date:** [March 17, 2026, 9:09pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/32 "2026-03-17T21:09:58Z")
> [@phs3](#): > > > [@LSLGuy](#): > > > > Which beats how they did it 100 years ago: they had specially trained people who would TASTE the urine and rule based on how sweet it was. Now there’s a job that probably nobody is sorry technology has replaced! You know.. sometimes, there’s things I just don’t need to know… ::sigh:: ”So, Mr. Tall Dark and Handsome, what do you do for a living?” ---
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [March 17, 2026, 9:11pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/33 "2026-03-17T21:11:44Z")
This is very helpful, thank you. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [March 18, 2026, 2:13pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/34 "2026-03-18T14:13:05Z")
> [@Mean\_Mr.Mustard](#): > > The interpretation of the other lab values would take this into account, potentially to the extent of invalidating some of the results. > > mmm > > ETA: Dilute urine drug screens would be flagged and likely re-obtained. To emphasize: the clinical interpretation should take this into account; the dipstick and the machine reading of it does not. Honestly though the most important bits of noting the specific gravity are in that context of drug screening (water added), and if real for a condition called diabetes insipidus, excess urination from an inability to concentrate. Fun history: diabetes referred to flowing through. Mellitus meant the sweet tasting sort; insipidus meant the bad tasting sort. Yes old time docs were hard core and tasted urine. I can’t think of too many times that the level of change from concentration altered my clinical decision making honestly. A little higher suspicion of UTI with less WBC or nitrites in a dilute urine maybe. The culture shouldn’t be impacted I don’t think. Decades ago we used to do routine urines as part of certain age physicals; that’s long past. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [March 18, 2026, 5:17pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/35 "2026-03-18T17:17:50Z")
I get annual blood work to check my liver and kidney functions and a PSA test among others. The last time a new lab did the work and I got an itemized billing. It listed 10 separate tests and the total cost was $1300. I have good insurance and got billed for $15. If I go to my online portal all the numbers are shown along with a range of expected results. Then my doctor summarizes everything and gives advice as needed. “Eat fewer carbs!” No problem, I’m a beef and cheese eater. ---
**Author:** ![Moriarty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/moriarty/32/49_2.png) [@Moriarty](https://boards.straightdope.com/u/Moriarty)\ **Post date:** [March 18, 2026, 6:16pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/36 "2026-03-18T18:16:28Z")
> [@jnglmassiv](#): > > > [@Ruken](#): > > > > researchers will normalize against bio markers like creatinine or viral fecal markers > > Thanks, having wondered myself. I think this must closer to the techniques used. There was a time in my life when I was being randomly drug tested, and couldn’t produce a clean sample. Instead, I purchased Dr. Green’s Synthetic Urine.. The boxes promoted the fact that they had creatinine in them, so as to demonstrate that it was a legitimate sample. In the 3 years I took tests, I never had a sample rejected. (The hard part of giving a sample was heating it up first. One of the markers of a fresh sample is that it is warm. The synthetic one included a hand warmer, but you could use a microwave. The challenge is carrying it between your legs as you wait to use the bathroom) ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [March 18, 2026, 10:20pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/37 "2026-03-18T22:20:22Z")
Urines are still tested fairly often in Canadian primary care and emergency departments. It’s a very inexpensive test, and can give useful information. In addition, female patients might require X-rays etc. and it is an inexpensive way to screen for pregnancy. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [March 18, 2026, 11:30pm UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/38 "2026-03-18T23:30:51Z")
On the Peds side as a screening test it rarely gave useful information but _often_ irrelevant positives that needed further evaluation to prove were normal. Most often small protein that was almost always normal orthostatic proteinuria, and finding asymptomatic bacteruria, which is better left unfound as it should not get treated. Guidelines dropped it in 2007 but practice changes in the wild took longer of course. In asymptomatic kids more harms than goods. ---
**Author:** ![puzzlegal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/puzzlegal/32/3827_2.png) [@puzzlegal](https://boards.straightdope.com/u/puzzlegal)\ **Post date:** [March 20, 2026, 12:53am UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/39 "2026-03-20T00:53:05Z")
My doctor tests my blood annually, but the last time i had a urine test was when there was a question about a UTI. And i think they just cultured it for bugs. On the other hand, when my husband was hospitalized with suspicion of cancer, they ran a ton of tests on his urine. (And also his blood, and also scans, and…) I don’t think the dilution matters all that much. Diluting the urine probably affects it by a factor of 2 or 4, and most of the normal ranges of stuff in urine are probably much large than that. (or, “if you see it, it’s a problem”, depending on what you are looking for.) ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [March 20, 2026, 1:26am UTC](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502/40 "2026-03-20T01:26:15Z")
With urines, the trick is “if you see it, make sure there’s enough of it or a better test before you decide it is a problem”. Urines are good screening tests - very cheap and fairly sensitive. But they aren’t very specific. You don’t need to work up tchotchkes. Unfortunately, in the United States given the medicolegal environment, I’m told, means you often do need to work up tchotchkes. So I understand the difference urinalysis plays at different age groups and in different countries and clinical settings. [Previous page](https://boards.straightdope.com/t/how-does-urinalysis-work-variable-dilution-issue/1028502.md?page=1)