Urinalysis (UA) Interpretation
Urinalysis or UA is a lab test frequently ordered in all types of medical settings: hospitals (ER, ICU, Inpatient floors), urgent cares, and outpatient offices. In many cases, the correct evaluation of the urinalysis is imperative to making an accurate diagnosis. To provide additional data, many labs perform urine microscopy, giving you exact details on the contents within the urine and quantifying the results. Read all about how to interpret the Urinalysis dipstick, as well as the urine microscopy in this article!
INITIAL URINALYSIS ASSESSMENT
Before you even run the urinalysis, you can tell quite a bit about the patient just by using your God-given senses.
The color of the urine is the easiest way to determine someone’s hydration status. Surprisingly, it can indicate other aspects of health as well.
Normal urine varies from very clear yellow to a darker amber color. Generally speaking, the less hydrated you are – the more concentrated your urine is with nitrogenous waste and electrolytes – thus darker urine. The more hydrated you are, the more dilute the urine, leading to clear yellow urine.
The first void of the morning is typically darker and more concentrated – this is normal. However, darker urine throughout the day should prompt an increased need to drink water. I think ALL nurses have realized that after a busy shift, their urine is much too dark.
When we see red urine – we typically think of blood. Medical conditions such as kidney stones (nephrolithiasis), UTIs, glomerular damage, or even malignancy. As little as 1mL of blood can cause a color-change, and the presence of red urine does not automatically mean large amounts of blood.
Rhabdomyolysis can cause myoglobin in the urine which has a red-brown appearance as well. It will also cause the Heme to react on the dipstick, but we will dive into that deeper in a bit. There are also various other factors that can cause red urine including certain foods such as Beets, Blackberries, and rhubarb; as well as different medications such as Propofol, Chlorpromazine, or Ex-Lax.
You may see a neon orange-red from the antibiotic Rifampin used in the treatment of TB, or phenazopyridine (Pyridium) used to treat bladder burning and discomfort during a UTI. Patient’s with a UTI will often take OTC Azo which will often cause this color or urine.
Other crazy Urinalysis colors:
Other foods, drugs, and disease processes can turn urine every color of the rainbow. Certain UTIs can cause Green or purple urine, Fava beans can cause brown urine, amitriptyline or IV promethazine can cause blue urine. While these are very interesting, they are also super uncommon and you probably don’t need to commit them to memory.
Urine turbidity is how clear the urine is. Cloudy urine is very turbid, and clear urine is, well… clear. When we see cloudy urine, our first thought should be infection which may be accurate. However, other causes of cloudy urine are casts, protein, and/or cellular debris from damaged kidneys. We will dive deeper into that later on.
Yes, sniffing urine can tell you more than you realize! Urine has somewhat of an aromatic smell, and stronger-smelling urine tends to indicate dehydration (concentrated urine). Infections tend to have a very distinct foul-smell of bacteria which is difficult to describe but does smell like ammonia as the bacteria often splits urea to form ammonia.
Sweet-smelling urine may mean spilling of glucose into urine from hyperglycemia. Lastly, If the urine smells like feces, a fistula might have formed somewhere between the GI tract and the Urinary tract.
Nah I’m just kidding – but did you know they used to taste urine to detect glucose in the urine?…. GROSS!
Once you’ve assessed the urine with your own senses, its time to send the urine off to the lab for urinalysis
The specific gravity indicates how dilute or concentrated the urine is. The normal range for this is 1.005 (being very dilute) to 1.030 (very concentrated). This can give the interpreter a pretty good idea of hydration status when looking at the urinalysis.
- Protein, ketones, and glucose, as well as recent IV contrast dye, can falsely elevate the specific gravity.
- Levels within the normal range indicate hydration status, 1.005 being very hydrated and 1.030 being very dehydrated.
- Levels below the normal range may indicate diabetes insipidus, renal failure, pyelonephritis, glomerulonephritis, psychogenic polydipsia, or malignant hypertension
- Levels above the normal range may indicate severe dehydration, hepatorenal syndrome, heart failure, renal artery stenosis, shock, or SIADH.
pH of urine stands for potential of hydrogen. The more hydrogen ions there are, the more acidic something is. The pH scale runs of 0-14, with lower numbers being more acidic, and higher numbers being more basic. Normal urinary pH tends to be about 6 but runs as low as 4.5 and as high as 8. Because the kidneys regulate your acid/base balance, any change within the body should show up in your urine. However, various different disease processes can interfere with your kidney’s ability to do this effectively.
- Diet: Cranberries and high-protein diets can cause acidic urine, whereas citrus fruits and low-carb diets can cause alkaline urine
- Medications: Sodium bicarbonate and thiazide diuretics can cause more basic urine
- Metabolic acidosis: Any excess hydrogen ions (acidity) should be secreted by the kidneys into the urine, causing a lower pH (<5.3).
- Kidney Stones:
- Alkaline urine typically is typically associated with Calcium oxalate, Calcium phosphate, Magnesium-ammonium phosphate, and staghorn calculi.
- Acidic urine typically is associated with uric acid and cystine calculi.
- UTIs: Urea-splitting bacteria such as Proteus and Klebsiella cause more alkaline urine (between 7.0-7.5).
- Renal Tubular Acidosis: Differentiating renal tubular acidosis is beyond the scope of this post, but pH can be used in the diagnosis and differentiation of RTA.
Related Article: “Arterial Blood Gas (ABG) Interpretation”
The urine normally has <150mg/day of protein and should be undetectable on a dipstick, but when this level exceeds 300mg/day, high protein in urine will show up on a dipstick. The urine protein dipstick is specific for albumin (a type of protein). Any damage to the glomerular basement membrane will let albumin and other larger particles pass through the membrane and into the urine.
Protein in urine typically used to evaluate kidney damage in diabetics, people with Congestive Heart Failure (CHF), or other causes of kidney damage. When there is high protein in urine, sometimes it is transient which means temporary and often benign. Benign causes of high protein in urine include dehydration, emotional stress, fever, heat injury, inflammation, intense activity, acute illness, or an orthostatic disorder.
All other causes of proteinuria involve the kidney – specifically the glomerulus or the renal tubules. Some common causes of glomerular proteinuria include Diabetic nephropathy, lupus nephritis, preeclampsia, various infections (HIV, hepatitis B, post-streptococcal glomerulonephritis), certain cancers, and certain drugs like Heroin, NSAIDs, and Lithium. Some causes of tubular proteinuria include interstitial cystitis, Sickle-cell, and nephrotoxicity from NSAIDs or antibiotics like aminoglycosides.
- Urinary concentration will impact the results, so correlate with the Specific Gravity. Very dilute urine can lead to underestimation of protein, and very concentrated urine can lead to overestimation.
- In general, the dipstick is a crude estimate, and evaluation by 24-hr urine specimen is the standard of care for ongoing proteinuria. Once renal cause is found, a Nephrology consult is warranted.
- In the acute setting, the dipstick for protein isn’t too informative as acute illness, inflammation, stress, and dehydration are common presentations and can cause a temporary elevation in urinary protein.
Blood in urine is detected with the use of Heme on the dipstick. The test for heme is very sensitive and can detect down to 1-2 RBCs/HPF. Thus, a negative dipstick theoretically excludes hematuria (blood in the urine). There are many potential causes of hematuria including UTIs, STDs, contamination, trauma/irritation, glomerular damage, coagulopathies, kidney stones, and malignancy.
- False-Negatives: Urinary ascorbic acid has been shown to cause false-negatives in some cases. Ascorbic acid is also known as Vitamin C – so the intake of dietary vitamin C or supplements can potentially cause false-negatives to occur. Some dipsticks do add a chemical to neutralize this effect. Overall, false-negatives are unlikely.
- False-Positives: Myoglobin (as during rhabdomyolysis), semen (recent ejaculation), alkaline urine >9.0, contamination from hemorrhoids, vaginal blood, or oxidizing compounds used to clean the perineum can all cause false-positive heme to occur in the urinalysis.
- A positive Heme requires urine microscopy for confirmation.
- If the patient is >50 years old and has persistent hematuria, they should be evaluated for malignancy.
- If hematuria also presents with casts and proteinuria – glomerular damage is likely.
- If hematuria presents with leukocyte esterase, WBCs, and nitrites – consider hemorrhagic cystitis
Leukocyte esterase is a component of WBCs that is released when these white blood cells are lysed. The presence of leukocyte esterase supports the diagnosis of a Urinary Tract Infection (UTI). However, the presence can also indicate various autoimmune disorders, STDs, kidney stones, or intra-abdominal infections.
- False-Negatives: Proteinuria, glucosuria, excessively concentrated urine, or tetracycline.
- False-Positives: Contamination with vaginal discharge, certain medications (ampicillin), salicylate toxicity, and strenuous exercise.
- Presence supports the diagnosis of UTI, whereas its absence means infection is unlikely.
Nitrates are present in the urine at baseline. Some species of bacteria, specifically of the Enterobacteriaceae species (E. coli, Klebsiella, Proteus, Enterobacter, Citrobacter, and Pseudomonas), release an enzyme called nitrate reductase which converts urinary nitrate to nitrite, causing nitrites in urine.
- Certain bacteria produce low levels of nitrate reductase such as enterococcus, and many bacteria do not produce any.
- This reaction requires dwelling time within the bladder to occur. Urinary frequency or the presence of a Foley catheter can make this impossible. It can take up to 4 hours of dwelling before nitrites are detected.
- A person might not intake a sufficient amount of nitrates in their diet.
- False-Positives: Azo dye metabolites and bilirubin, as well as letting the urine sit for too long can produce false-positives. Higher specific gravity reduces the sensitivity.
- False-Negatives: Ascorbic acid can produce false-negative.
- If negative, it really doesn’t mean much. If positive, then it is highly likely an infection is present.
When serum glucose spills into the urine – this is termed glucosuria. Typically, glucose in urine does not occur until the kidney glucose threshold is reached – which is around 180mg/dL. As you can tell, this can be useful for evaluating hyperglycemia in the setting of diabetes. However, periods of stress or fever have been known to cause small amounts of glucose within the urine as well, so glucose in urine does not automatically mean diabetes.
- Ascorbic Acid (vitamin C) has been known to cause false-negatives.
- Glucosuria can indicate hyperglycemia in undiagnosed diabetics when blood-work is not obtained.
Ketones are released from fat cells when fat metabolism is increased. Most notably this occurs with Diabetic Ketoacidosis (DKA). However, ketones may also be present in low-carb ketogenic diets when dietary carbohydrates are kept below 50 grams per day, as well as with starvation such as during acute illness with decreased intake or nausea/vomiting. I see this all the time in the ER.
Urinary bilirubin may be present in low amounts, but increased levels are due to abnormalities of bilirubin metabolism or liver function. Other causes include hepatitis, hepatobiliary obstruction (gallstones), hemolysis, liver parenchymal disease, constipation, or intestinal bacterial overgrowth. The urinalysis must be sent immediately as bilirubin is unstable, especially when exposed to light. Clinical Significance:
- Urinalysis Clinical Significance: The presence of bilirubin may indicate elevated LFTs, but overall does not seem to add significant information toward diagnosis.
Crystals, as the name implies, are crystallizations within the urine. Crystals in urine can be normal as long as they are composed of substances normally found within the urine.
- Ethylene glycol ingestion: Typically presents with calcium oxalate crystals (“envelope-shaped”) and acute kidney injury
- Tumor Lysis Syndrome: Presents with large amounts of uric acid crystals (“diamond” or “barrel” shaped) and acute kidney injury
- Gout: May see uric acid crystals
- Cystinuria: Present with cystine crystals (“hexagonal”)
- UTIs: Magnesium ammonium phosphate and triple phosphate crystals (struvite) are “coffin-lid” shaped and seen with UTIs caused by urea-splitting organisms such as Proteus and Klebsiella.
Bacteria are NOT normally found in the urine as it should be a sterile environment. If found, it usually indicates infection or contamination.
- Bacteria multiply rapidly if the urine specimen is left standing for too long at room temperature.
- If there are leukocyte esterase +/- nitrites present with <15-20 epithelial cells/HPF, then infection is highly likely. Consider starting empiric antibiotics if symptomatic and obtain a culture and sensitivity for confirmation.
RBC: Normally there are less than 2 RBCs/hpf. Microscopic hematuria is defined as the presence of at least 3 RBCs/HPF. Microscopic hematuria confirms a heme+ dipstick.
WBC: 2-5 WBCs/HPF or less is normal within the urine. If higher, this indicates possible infection, inflammation, or contamination. Most of the WBCs found in the case of infection are neutrophils.
Epithelial: Squamous epithelial cells are the skin cell of the external urethra. >15-20 epithelial cells/HPF indicates contamination.
Casts are tube-like protein structures made of various cells. Low urine pH, low urine flow rate, and high urinary salt concentration promote cast formation by favoring protein denaturation and precipitation. The presence of casts, other than hyaline casts, represents pathology within the kidney itself.
Hyaline casts: These can be present in normal healthy adults and are nonspecific. They can be found after strenuous exercise or dehydration, as well as with diuretic use.
RBC casts: Likely indicates glomerulonephritis or vasculitis.
WBC casts: Uncommon, but when present is usually seen with tubulointerstitial nephritis and acute pyelonephritis, but also seen with renal tuberculosis and vaginal infections.
“Muddy-brown” granular casts: are diagnostic of acute tubular necrosis, the leading cause of Acute Kidney Injury.
Waxy casts: Consistent with acute or chronic renal failure.
Broad casts: Consistent with advanced renal failure.
Fatty casts and lipiduria: Indicates Nephrotic syndrome
Renal tubular epithelial casts: seen in acute tubular necrosis, acute interstitial nephritis, and proliferative glomerulonephritis
Hopefully, this gives you a pretty good idea of how to interpret a urinalysis. Whether you are a nurse, an advanced practice provider, or a physician, this skill is important to have. If there are any other diagnostic interpretations you would like to see, please leave a comment below!
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- Lerma, E. V. (2015). Urinalysis. Medscape. Retrieved April 1, 2018, from https://emedicine.medscape.com/article/2074001-overview
- Meyreir, A. (2020). Sampling and evaluation of voided urine in the diagnosis of urinary tract infection in adults. In T.W. Post (Ed.), UpToDate. From https://www.uptodate.com/contents/sampling-and-evaluation-of-voided-urine-in-the-diagnosis-of-urinary-tract-infection-in-adults
- Tintinalli, J. E., Stapczynski, J. S., Ma, O. J., Cline, D., Meckler, G. D., & Yealy, D. M. (2016). Tintinallis emergency medicine: A comprehensive study guide (8th ed.). New York: McGraw-Hill Education.
- Walk, R. W. (2018). Urinalysis in the diagnosis of kidney disease. In T.W. Post (Ed.), UpToDate. Retrieved April 1, 2018, from https://www.uptodate.com/contents/urinalysis-in-the-diagnosis-of-kidney-disease