Definition of "Urinalysis"
Urinalysis (U/A, aka Routine and Microscopy, R&M) is an array of tests performed on urine.
- Urine dipstick, which is composed of 10 different chemical pads which change color when immersed and then removed from a urine sample. It can be read within 60-120 secs, although certain tests require longer. It tests for, noting that the reference values are for the prima facie value, are NOT displayed on the dipstick which only shows COLOR changes:
- Glucose (GLU), which should normally be from 4-6mmol/L. Glycosuria (aka glucosuria) is where it is elevated, and is most commonly due to untreated diabetes
- Bilirubin (BIL), is where CONJUGATED bilirubin is detected in the urine, indicating hepatic or post-hepatic disease. In contrast, biliuria means the presence of any bile pigment in the urine
- Urobilinogen (URO), which is a colorless by-product of bilirubin reduction via bacterial action in the intestine. Elevated urobilinogen can indicate pre-hepatic or hepatic disease. Urobilinogen is converted to the yellow pigmented urobilin apparent in urine
- Ketones (KET) or acetones, for Diabetes. Values are normally <0.6mmol/L
- Specific gravity (SG), where water itself is 1, and urine thus should be between 1.003-1.035 to indicate normal kidney function. Specific gravity >1.01 however, may indicate mild dehydration
- Occult blood (BLO), which is blood that can't be seen with the naked eye, but can be with a microscope. Normal urine shouldn't contain any RBC's except women during menstruation
- pH, which is normally 6.2, within a range of 5.5-7
- Acidic urine, in someone with hyperuricosuria can cause formation of uric acid stones in the kidneys, ureters, or bladder. Can also be caused by diets high in protein from meat and dairy, or alcohol consumption. Drugs can also do it, e.g ammonium chloride, chlorothiazide diuretics, and methenamine mandelate
- Basic urine, can be caused by a diet high in fruit and vegetables, or drugs e.g. acetazolamide, potassium citrate, and sodium bicarbonate
- Protein (PRO), indicating proteinuria
- Nitrites (NIT), for UTI's
- Leukocyte esterase (LEU), for UTI's
Patient information
What do you do in a urine dipstick?So it involves getting a sample of urine, and dipping one of these test strips into the urine, to test it. You can test sugar. Bilirubin. Ketones. Specific gravity. Blood that can't be seen with the eye. pH. Protein. Urobilinogen, which if it is higher than normal, can indicate a problem at or before the liver. Nitrites and white cells for UTI's.
So urine glucose. That's your BSL's, right?
Not really, BSL's is sugar in blood. This is in urine. So urine glucose is from 4-6mmol/L. It's a little different from blood glucose, which varies a lot throughout the day, but is usually >4mmol/L even when not eating. When not eating, it should get higher than >8mmol/L, or that's starting to sound like diabetes. Usually, nearly ALL glucose is reabsorbed in the PCT of the kidney, but the capacity may be exceeded if BSL increases a lot, as it does in diabetes, the threshold being 40-45mmol/L.
Bilirubin in urine. That's bilirubinemia, right?
Again, not really. This is in urine, not blood. So the kidney can't touch unconjugated bilirubin, because it's not water soluble. However, with conjugated bilirubin, if the liver's function is impaired, or when drainage of bile is blocked, some conjugated bilirubin leaks out of the liver, and appears in the urine.
How does it differ from urobilinogen?
So this is where conjugated bilirubin is successfully excreted from the bile duct into the intestine, and converted by bacteria in the intestine into urobilinogen and stercobilinogen. Some of this is reabsorbed by the intestine into circulation, and filtered out by the kidneys. Urobilinogen is thus elevated in hemolytic and liver disease.
Ketones in urine. What makes it elevated?
They're products of metabolism of fatty acids, so they're made because fats are getting metabolized. This can happen because of starvation, malabsorption, inability to metabolize carbohydrates (as in diabetes), or losses from frequent vomiting.
Specific gravity, the weight of urine?
Sort of. We compare it with water, which is considered to be 1. It should normally be a little heavier than water. However, if it's heavy, it probably means there is dehydration, reducing the water content in comparison.
pH of urine. How does that work? Urine is acidic right? It sort of burns?
Neutral pH is 7, so yes, urine is sort of acidic, around 6.2. Acidic makes it more likely for uric acid stones to form, can be caused by diets high in protein. Urine can be basic, with diets high in fruit and veggies. Certain drugs can also make urine pH go both ways, depending on the drug.
Protein in urine. What does this mean?
So it usually means early kidney disease. Small proteins like albumin are let through by the glomerulus, and needs to be reabsorbed by the tubules.
Nitrites and leukocyte esterase in urine? Urine is usually sterile, right?
Nitrite indicates a specific cause of UTI's by Gram negative bacteria, that have enzymes that reduce nitrate present in urine, to nitrite, so it can mean E coli, Enterobacter, Klebsiella, Citrobacter, or Proteus. Leukocytes can sometimes be found in urine, due to vaginal contamination, but leukocyte esterase is found only in urinary infection.
- Microscopy, which tests for:
- Hematuria (RBC)
- Pyuria (WBC)
- Eosinophiluria
- RBC casts
- WBC casts
- Granular casts
- Crystalluria
- Calcium oxalatin
- Waxy casts
Patient information
Urine microscopy. What's the difference between a dipstick and microscopy?Dipstick is where you dip a chemical test strip in urine. Microscopy is where you view urine under a microscope. So you might find red or white blood cells in the urine, and a few other things too.
It can also involve:
- Urine culture, which is a microbiological culture of urine sample, detecting bacteriuria, indicated when UTI suspected. Sensitivity testing (aka MC&S) isw here the effectiveness of antibiotics against bacteria present is trialled
- Midstream urine (MSU) is used to obtain sterile urine (i.e. no bacteria present), important to test for urine infection, and which antibiotics to use. To obtain a sample of urine from the middle of the Pt's bladder, involves passing some urine into the toilet, before catching urine mid-stream in the sterile bottle
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- Urine catheterization
- Suprapubic aspiration (aka bladder aspiration), involves putting a needle into the bladder just above the pubic bone. It can be used to collect urine in a child who isn't toilet trained, especially to Dx UTI's
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Patient information
How do you test urine?So to test urine, you need to collect it. You don't just want any urine, because there's usually some contaminants, particularly at the start of the stream. So you can get the middle part of the stream. You can use a tube, which feeds directly up to the bladder to get urine, so it won't be contaminated. You can also get it from a needle inserted into the bladder, just above the pubic bone.
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