The Yellow River…by I.P. Freely (and other ways we look for answers in the urine)
Do you remember laughing at these “books” or was it just me?
-Under The Bleachers… by Seymour Butts
-Gotta Go…by C.U. Later
-Ten Years in the Bathtub…by Rink Lee Prune
For whatever reason I always think of those funny titles when I order a urine test on a patient. And I order those fairly regularly. Most people think of a urine test, concisely known as a urinalysis, as an order we send when we want to check to see if a patient has a bladder infection (or urinary tract infection, UTI). But there are many more truths to be found in a urinalysis other than the sole suggestion of a UTI. In fact, many times a urine culture (different test) is needed to diagnose a UTI. But I think a brief review of the OTHER diagnoses that are made, confirmed, or suggested by certain urine results will be interesting and might even be helpful, so let’s do it.
Obtaining the Sample
Before we even get to the examination of the fluid, let’s talk about how we obtain the sample, because it’s one of the most important parts of this whole story. Normal urine itself is a sterile fluid. It only gets contaminated if there’s an infection in it or if it comes into contact with germs on the skin on the way out of the body. Think about it: a contaminated sample with germs from outside the body isn’t very helpful because it doesn’t reveal what the status is of the urine fluid itself. That’s why you’re asked to clean off the urethral opening (where the urine exits your body) before you obtain the sample, and also why you’re asked to get a sample from “midstream.” Not too complicated, except if you’re IN DIAPERS and NOT POTTY TRAINED. What then? This surprises many parents, but in this situation we typically do an “in and out” catheterization, where a very small tube is inserted into the urethra using sterile technique to obtain a clean sample. While usually not sharply painful for anyone, I won’t advertise that it is a fun procedure, but it is quite harmless and quick and obtains a sample from which conclusions can be drawn. Understanding that this is a necessary procedure in children for whom obtaining a clean urine sample is impossible is extremely important.
So once we have the physical sample, it gets processed in the lab and certain components are delivered back in the report. A few of these parameters can be pivotal in making many diagnoses.
This number relates to the density of the urine fluid or how concentrated the urine is. Getting technical, the specific gravity measures the ratio of urine density compared to the density of water. Helpful when getting a sense of how dehydrated a patient is. The higher the spec grav, the more concentrated their urine is. This can also be important in some diseases where the kidney fails to appropriately concentrate the urine. These patients may barely drink any fluid at all and yet they pee out urine that’s too dilute, which is a problem for maintaining normal balance of electrolytes. The name of this disorder is diabetes insipidus, which is different from the more common diabetes mellitus. Confusin’… (imagine all the fun I had taking tests in my first few years of medical school).
Whenever I see someone “spilling glucose” into the urine I worry about diabetes mellitus (regular ol’ diabetes). Sometimes this is a good screening tool when there is a concern for diabetes in conjunction with a blood glucose test. Another condition that can cause an elevated glucose in the urine is hyperthyroidism. Confirmatory blood tests need to be sent to look at the various thyroid hormone levels to make this diagnosis.
Ketones are a chemical produced in the liver that the body uses to generate energy from fat when sugars and carbohydrates aren’t available. Their presence in the urine is a good proxy for dehydration, and is common in people who are acutely sick with a vomiting illness, for example. It’s one of the main indicators for worsening diabetic control.
Red blood cells in urine can be nonspecific, and can indicate many things: girls who are menstruating at the same time the sample is obtained, or kidney trauma, or inflammation in the kidney due to processes like autoimmune diseases, or post-infectious complications that can occur after a strep infection.
There are some kidney diseases that cause abnormal amounts of proteins to be eliminated in the urine, and most of them are autoimmune.
White blood cells are infection fighting cells and as I mentioned above these are what we look for most commonly when we look for a bladder infection, but it’s important not to be narrow minded about this result and consider other infections as well, such as sexually transmitted infections, especially in older patients. A certain low number of WBCs in the urine is absolutely normal.
So there’s my hyper condensed version of “understanding the urinalysis 101” that has taken me lots of years to distill down to a few pages. I hope you come away from reading this with a broader sense of the wide range of information that can be obtained from taking a look at a short lab result readout. Additionally, I hope the famous fictitious “book titles” at the top of this post gave you a quick smile. What? You’d like a few more? Well, alright. I’ll leave you with these:
-Interesting Places Around the World by Ben There & Don That
-Magical Bed Wettings by Peter Pants
-Long Walk Home by Miss D. Bus