Urinalysis Interpretation

This “pee in a cup” test is simple and informative. Although used most commonly to detect urinary tract infections, this test is also a valuable tool to screen for other disease processes as well. However, this test is far from perfect and abnormalities often require further testing before a diagnosis can be made.

In a perfect world, the urine specimen is obtained mid-stream as the initial urine stream often contains contaminants of the urethra tract rather than an accurate representation of urine from the bladder. Storage of urine samples can also make a difference as temperature and time elapsed before testing can change the results.

Certain parts of this test can also result in false-positives and false-negatives. For example, the Heme test detects hemoglobin molecules that are found in red blood cells and is used to find blood in the urine. However, those same molecules are in other disease processes like hemoglobinuria and myoglobinuria. So even though a dipped urine specimen is positive for red blood cells, it may mean something else entirely. This is called a false-positive. A false-negative example is found with leukocyte esterase (enzyme found in white blood cells) and can indicate infection. However, this enzyme is suppressed when the urine is concentrated or if there are large amounts of glucose in the urine. So even if there are WBC in the urine, the test will be negative if concentrated or glucose present.

The initial part of the test is to determine color and turbidity (cloudiness). Urine typically comes in clear to dark yellow. However, some conditions can cause discoloration outside that normal range (I typically get a phone call with those). Blood is the most common cause of discoloration (hematuria). The second is medication.

Specific Gravity is how concentrated the urine is. This is an excellent reflection of how well hydrated the patient is. Clear urine will have a low specific gravity indicating well hydrated. Dark yellow urine has a higher specific gravity indicating mild dehydration. The exception is if there is a high glucose content as that will increase the specific gravity due to extra glucose molecules in the urine.

The following tests are rated as trace, 1+, 2+, 3+ to determine how much is present. Like any test, the results are interpreted with patient symptoms.

The glucose test is pretty self-explanatory. This can be a decent screening tool for diabetes that does not involve needles, but it may miss more mild cases. Diabetes is diagnosed when fasting blood glucose is above 126 on two separate occasions. When blood glucose is elevated above 160 in the blood, glucose will spill into the urine. Therefore the diabetic range between 126-160 will be missed on urine screening.

Ketones are created when glucose is not available for use. Ketones are derived from fat to supply alternative energy source for cells. This can be seen in diabetics, starvation, and acid disturbances in the body. While informational, this finding rarely results in change in decision making.

Leukocyte esterase is an enzyme secreted from white blood cells. When present, it can indicate an infection. If an infection is suspected, a urine culture should be sent for confirmation as there are other states where the test will be positive when infection is not present.

Heme is most commonly a reflection of the presence of blood. There are many reasons for blood including infection, cancer, kidney stones, etc so when heme positive, further workup starting with microscopic evaluation is indicated. Hematuria (blood in urine) deserves its own separate post.

Nitrates are positive due to the presence of nitrite reductase. This enzyme is produced by most bacteria and can indicate an infection. Not all bacteria produce this enzyme so this should not be the only indicator of infection.

Protein can indicate kidney disease rather than bladder symptoms. The kidneys are a filtering system that keeps the good stuff in and excrete the undesirables. Protein is the good stuff so when it shows up in the urine, it can indicate the filter is not working correctly. A flaw of the urine dip is the variability of results based on factors unrelated to protein. Concentration of the urine can greatly change the results so if positive and reproducible, further testing is necessary.

The next step of urine evaluation extends beyond the basic dipstick test and is called microscopy. The urine is spun to separate the liquids and solids out. After most of the liquid is removed, the sediment in urine is examined under a microscope. This can confirm the presence of all of the below:

• White blood cells are present with inflammation, most commonly infection.
• Red Blood Cells indicates actual blood which can happen with infection, cancer, stones, menses, and inflammation
• Crystals are markers of metabolic disease and often found in presence of kidney stones
• Epithelial casts indicate contamination of the specimen by genital tract and reflects the quality of the urine sample. Less is better.
• Casts are findings in the urine that indicate a kidney rather than bladder problem. These are damaged cells cast off by the kidney in times of stress or disease.
• Bacteria and fungal are commonly found in the urine, but usually in small quantities unless infection present.

The “pee in a cup” test gives the clinician a lot of information. The patterns of positive and negative results can direct us to the next step of evaluation and management. Hopefully you find the above information helpful.

What does it sound like when a pterodactyl uses the bathroom? 
 - Nothing. The pee is silent