Urinalysis – The Golden Fluid
Yes – the golden fluid. I remember a veterinarian many (many, many…) years ago, early in my career, using this term and I have never forgotten it. It truly is amazing how much information the clinician can get from a urinalysis. It can be used for disease detection, monitoring, and screening (such as with diabetes, liver problems, and Cushing’s). It is an important part of both diagnostic evaluation as well as a preventive medicine program. It can reveal hydration status, upper and lower urinary tract function, inflammation, infection, and neoplasia. It can identify the presence of excess protein, glucose, white blood cells, casts, red blood cells, bacteria, and crystals which indicate the need for further evaluation (hmmmm…such as with ultrasound!) It is critical that every technician be skilled in performing a complete UA in house; a sample can undergo changes in pH, bacteria count, and crystal formation while waiting to be shipped to the outside lab. Assistants should also become skilled at analysis of physical characteristics and dipstick, and proper slide preparation - and also look at as many sediments as possible while referring to the numerous urinalysis reference manuals that are probably sitting in your hospital lab drawer right now. There is also plenty of online CE through vetmedteam.org and vspn.org to help increase expertise. As with most skills, practice practice practice is the key to becoming comfortable.
There are 4 steps in performing a proper urinalysis:
Note time and method of collection (cystocentesis, catheterization, free catch, off table or floor, etc). If a client brings you a sample, ask if it was refrigerated and how soon after collection.
Physical characteristics – analysis of color, clarity, odor and urine specific gravity (USPG). Color terms can include clear, pale yellow, straw yellow (considered the color of normal urine), deep yellow, amber, red, brown. Clarity terms can include clear, hazy, cloudy. Odor terms can include benign (considered the odor of normal urine), sweet, strong. I’m sure there are others in the literature. Make sure you measure USPG with a refractometer (procedures for this can be found in the PCV and total protein article). USPG on the strip is not accurate. On my refractometer the USPG scale is on the far right; a reading would be recorded, for example, as 1.032. If it is above your available scale, record as >1.040 or whatever your highest scale number is. There is a way to calculate the exact USPG using a urinometer, but I’m not sure how many hospitals even have one of these.
Biochemical test – dipstick analysis
Follow closely the directions on your jar of dipsticks, but most follow the same guidelines. Thoroughly mix the sample. Completely dip the test area of the strip into the urine and remove immediately, or use a pipette to transfer urine to the test pads. Remove excess urine from the strip by tapping the edge on a paper towel. Read results according to the times on the color chart. Be ready with the strip – some of them require all the pads to be read in 60 seconds, and others will range from 30 seconds to 2 minutes. Hold the strip next to the test pad well before your earliest time so you are ready and not fiddling with your stuff when you should be reading the color. The longer you go beyond the recommended reading time the more inaccurate your evaluation will be. And remember reading a color is subjective anyway.
To remember –
- The leukocyte pad is not accurate for cats
- If the urine is very off color, red or brown, you will have a very difficult time reading your dipstick. Try spinning the urine first and using the supernatant, most times the urine will clear up as the RBCs sink to the sediment.
- Yes, you can use the supernatant for a USPG measurement
- You may be able to obtain a card that has the dipstick color scale on it, making it easier to read rather than holding the strip up to a round bottle.
Microscopic evaluation – sediment analysis
- Pour 5-10 ml of your sample into a NEW centrifuge tube (or as much urine as you have!) It is not fun when your tube breaks in the centrifuge and you completely lose your sample!
- Add a balance tube and spin on your setting for urine, or 2000 rpms
- Poor off the supernatant (but always save it for the day!), resuspend the sediment in the remaining small amount of urine. Flick the bottom of the tube to mix the sediment, or as I prefer use a long pipette with bulb to suck the sample up just an inch or so and push back out. Place a drop on a new slide, add a coverslip and your sample is ready to examine.
- I know some people prefer to look at a stained sample. The problem with this is that stains can very quickly become contaminated and then you end up with all kinds of weird stuff on your slide that you need to try and figure out if real or artifact. If you are already dependent on stained slides, try this: Make 2 samples on the same slide, one without stain, and one after you have added stain. A coverslip on each of these drops. Then start looking at both samples, and I bet you will see a difference in the amount of debris. Eventually try to eliminate the stained sample. The only thing I ever use it for, very occasionally, is to better help me distinguish an RBC from a WBC, for some reason difficult on some samples.
- If you really like stain, there is a much better alternative. Make a smear of your sediment and stain using diff quick stain. This can often beautifully highlight bacteria, WBCs, and epithelial cells. I often make one of these slides if I suspect neoplasia based on the normal sediment exam. Much better way to get a look at those possibly abnormal epithelial cells. Check out the stain procedure in the article “Skin Cytology – slide prep”.
- The sediment should be viewed first under low power (100x) with subdued light, continuously moving the fine adjustment knob so that all depths are viewed. Scan the entire slide and observe for casts, crystals and other elements present. Switch to high dry power (400x) when necessary. Don’t forget to examine the periphery of the coverslip, casts and crystals can hide there. If you are looking at a diff quick slide, start on low power, then evaluate on high dry. You can also add immersion oil and examine with the immersion oil lens, just like a blood smear.
- Become serious about learning to identify all of the elements on a urine sediment! Drag out those reference manuals, take an online course. It takes a lot of practice and dedication to become skilled. You cannot afford errors when the doctor is relying on your evaluation to determine medications and/or further diagnostics.
Reporting Scheme for Urine Sediment
|Element present||area of slide examined||reported as|
|Cells (rbc, wbc, epithelial)||average # 10-15 HP fields||/hpf|
|Casts||average # 10-15 LP fields||/lpf|
|Crystals||average #10-15 fields||0-3/hpf|
|TNTC (too numerous to count)|
|Bacteria, sperm, fat, debris||average #10-15 fields||1+ small amt|
|2+ moderate amt|
|3+ marked amt|
Here is how I perform the most time efficient UA (and aren’t we all pressed for time?!):
- First is to get your sample spinning
- While spinning, get the dipstick running
- If you are good you can do the USPG before your dipstick is ready to read
- You are SO GOOD that now your sample is not even done spinning and you are ready for it! Be even more efficient and read a fecal while you are waiting.
- Don’t forget to record your results either on the paper chart, with a sticky UA reporting label, or directly in the patient’s medical record under the UA electronic form.
***Call the company who makes your brand of dipstick. They should be able to provide you with free stacks of urine reporting sheets***