We’ve got an FQ about poo at the moment, so why not one about pee.
When testing for components in urine, how do they account for the fact it may be quite concentrated or quite dilute? Suppose the normal number of something is 10mcg/liter. Wouldn’t results jump all over the place depending on how much water the patient drank recently?
I suppose if they’re looking for, say, drug residue, they’re looking for “any” amount, which is why pot smokers drink a lot of water and pray. But if they’re looking for something that’s supposed to be within a range, I don’t know how urine is a good test at all.
Additionally, is urinalysis really a routine thing anymore? I haven’t had a doctor request one in many years.
One of the components of a standard UA is a urine specific gravity, which would indicate a highly dilute sample if present. 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.
I get a well-baby checkup from my PCP every 3 months. Have for years and years. A urinalysis is run annually. If you’re not getting regular check-ups, you’re probably not getting UAs either.
There are some diseases & conditions (ref Beck) where a UA is directly diagnostic.When you go to see the doc about some specific problem or other, they’ll also not bother with a UA unless you’re suspected of having one of those relevant conditions.
I think it depends - I see my PCP about every three months but it’s not for a well-baby checkup. . Urine every time until today. The difference today is that he asked me when I last had blood drawn, and I told him the hematologist and endocrinologist draw it every vist so twice in the last 2 weeks (I try to bunch up dr visits.) Since he can see those results , he didn’t draw blood today and I guess that was the reason for no urine.
This could be a good example. Dr. Google says normal sugar is 0-15 mg/dL. Suppose, on an average day, I have 14. That’s OK, but something to watch perhaps. Next time, I’ve been chugging gatorade because I have a pot test later on, and have near 0 – that’s a distorted result. Time after that, I forgot to drink water the day before, and I have 28, but that’s only because everything’s been concentrated down into a smaller volume of liquid. But the doctor doesn’t know that, sees “28” and knows it’s way over the normal level.
Is it true what @Mean_Mr.Mustard said, that they test specific gravity, then adjust interpretation of everything on that basis?
OK, well here’s a dumb question then. (I may not quite understand what specific gravity is.) Are they determining how much of the urine is non-H2O, expecting the answer to be, say, “10” for an average sample, then if the particular patient’s is 5, they double every result, and if the non-water content is 20, they halve them?
You’re right, that is the purpose of the urine sample you give at your FAA medical exam. But what the doc’s helper does with the urine is not a true “urinalysis” which would produce a number of interesting chemical readouts.
Instead they have a little chemically treated test strip they dip in the urine which turns color if the urine has sugar in it. Which is diagnostic for diabetes and only diabetes. Then the rest of the sample is dumped.
That’s exactly how I got diagnosed w diabetes. At my FAA first class renewal. Surprise! You’re unemployed. Or at least grounded until further notice.
I got much more – I have results for Leukocyte esterase, Nitrates, Bilirubin, and many others besides Glucose. Now maybe Glucose is the only one the FAA cares about, but they did more.
In my last two tests my specific gravity was at the high end of normal (1.25).
Specific gravity is a ratio between the density of a sample and the density of a standard.
A solution changes in density as the concentration changes. (For water-based solutions, I believe that in general, the more concentrated, the higher the density.)
So there’s a “standard” density of urine to which the density of the specimen is compared, and the specific gravity is the calculated ratio of the measured specimen density and the standard density value.
(However, reading stuff provided by Google tells me specific gravity is actually measured with a color-change dipstick, which implies some kind of consistent color change based on the concentration of some specific substance in urine.)
I wonder if it has to do with whether a person has diabetes/borderline/high blood sugar (and/or is a likely candidate based on their weight or other clues). No blood workup of mine has ever shown high blood sugar and I have no other indicators, and like I said, I don’t even remember my last urinalysis, it’s been so long - 20 years or more.
You would have to chug a lot for it to spill over into the urine in an otherwise healthy urinary system. This occurs when your blood glucose level overwhelms your kidneys’ ability to process it.