Normal urine varies from yellow to amber, depending on its concentration. Edible dyes, including those in medications and certain illnesses, can change its color (Table 19-3).
Table 19-3 Urine Color and Associated Pathology ||Download (.pdf)
Table 19-3 Urine Color and Associated Pathology
|Yellow foam||Bilirubin||Obstruction of bile duct system or severe hepatocellular damage|
|Greenish foam||Biliverdin||Increased red cell destruction or liver pathology produces bilirubin oxidation product|
|Reddish||Hemoglobin, porphyrins||Renal or bladder bleeding, pernicious or hemolytic anemia, lead or barbiturate poisoning, congenital porphyria|
|Light red to
red-brown||Hemoglobin||Renal or bladder bleeding, malaria, paroxysmal hemoglobinuria, transfusion reaction|
|Orange||Pyridium||Iatrogenic (urinary analgesic)|
|Smoky red to brown||Blood||Renal or bladder bleeding, acute nephritis, kidney infarction|
|Dark or smoky||Phenol||Phenol poisoning|
|Brown to black||Melanin||Leukemia, malignant melanoma, ochronosis, liver carcinoma|
Urine is easily tested with multifunction sticks. These can test for the presence of protein, glucose, ketones, nitrites, bilirubin, urobilinogen, red blood cells (RBCs) or free Hgb, white blood cells (WBCs), leukocyte esterase, pH, and specific gravity, depending on the stick used. The strips must also not have deteriorated due to moisture or temperature.
Cloudy urine can be due to a variety of reasons. Usually, it is due to the presence of blood (generally pink or red), crystals, or infection. If signs and symptoms of infection are present, do the three-glass test to improve the chance of localizing the infection. During a single void, collect the first 5 mL in one container. Collect nearly all the rest of the urine in a second container. In the third container, collect the last 5 mL or so. If the first container is very cloudy, but the urine clears in the second and third containers, the infection is probably urethral. If the second and third containers are cloudier than the first, the infection probably resides in the bladder or kidney. If the third container is the cloudiest, the prostate is probably the culprit.
Rather than spinning urine, with or without a Gram stain, an easier method to determine the presence of infection in a good urine sample is to look for ≥1 bacterium/HPF (high-powered field). That correlates well with >100,000 organisms/mL if the same specimen is cultured.
Even the ancients knew that urine that tastes like sugar indicates diabetes mellitus. Go ahead—taste it. That's real austere medicine. (I prefer to use the test strips.)
If a urine dipstick to measure protein is not available, another way to check for proteinuria is to fill a test tube three-quarters full with a clean-catch specimen and heat the top half of the tube over a low flame. Use metal tongs to hold the tube, and rotate the tube while heating it so that the glass does not shatter. If the urine turns cloudy and white, add a few drops of vinegar (2% acetic acid). If it stays cloudy or gets whiter, there is protein in the urine.22 Protein can appear in the urine due to infection, bleeding, intrinsic renal disorders, or preeclampsia.
Gram stains of urine specimens are done either on spun sediment or on bacteria from urine cultures. Gram-staining slides can provide a tentative identification of bacteria in urine, pus, sputum, cerebral spinal fluid (CSF), and bacterial cultures. Although not highly accurate for identifying species, a Gram stain enables the clinician to make an educated guess about the appropriate antibiotic to use, if the information is combined with knowledge of the clinical situation. The test requires several chemical solutions to prepare the slide and a microscope to view the end product.
The basic "sure-fire" technique is to make a slightly uneven smear from the specimen. Unless you are in a grave hurry, air-dry rather than heat-fix the slide. Wear gloves to avoid staining your hands rather than using forceps to handle—and often drop—the slide. Once the slide is dry, cover the slide with ammonium oxalate crystal violet and wash off the back (not the front) of the slide using a thin stream of water. While smears of pus are relatively durable, urine sediment is fragile and, if washed directly, will go down the drain. Then, do the same with Gram's iodine solution. The amount of time the stains are on the slide (3 seconds to 3 minutes) does not matter—but they must be identical. Then, hold the slide with one end slanting down, and drip on the acetone-alcohol until the color draining from the slide sharply decreases. Immediately wash the back of the slide. Pour on the safranin and immediately wash it off. Dry the back of the slide and, if in a hurry, dry the front by waving the back of the slide over a Bunsen burner, alcohol lamp, or similar heat source. With uneven smears, WBCs in the thin areas will have pink nuclei, but they will be bluish or purple in the thicker areas. Note that the organisms may vary in color. That is usually because, unlike laboratory specimens grown at the same time, "bugs" from real specimens are at different stages in their life cycle, and hence will have different colors.23
Draw conclusions with care—accuracy depends on training and skill. Gram-positive bacteria may appear gram-negative if they are old, if the patient has been treated with antibiotics, or if you washed the stain off the slide. Artifacts, such as particles of crystal violet, may be misinterpreted as cocci or bacilli. Some material from the smear may have disappeared during staining if you did not fix it properly or if you made the smear too thick.