Urinalysis (U/A)

Urinalysis can be used to detect a wide variety of disease states, particularly disorders of the urinary system (obviously). Urinalyses are easy to misinterpret or ignore, however - hopefully this brief guide will help. Be aware that U/A's can degrade quickly - casts are especially prone to rapid degradation. If you suspect that casts may be present, order the U/A stat.

An order of U/A by itself will not include a culture (which you need to order to determine what type of bacteria may be present). You should order a "U/A" and also a "Culture if U/A Positive" (you can just write "Culture IFUAP") if you suspect cells or bacteria to be present - the lab will run the culture if there is positive leuk est, nitrites, or wbc's. The culture won't be run if the U/A shows it to be unnecessary. Ordering "U/A with Culture" means you get both whether you need them or not.

Similarly, if you are looking for tumors (particularly bladder tumors) you should order a "urine cytology." A U/A by itself only includes the labs you would find on a dipstick. The lab will automatically add tests for micro (looking for crystals, cells, casts) if indicated, however, so you don't need to worry about a special order for these tests.

Color: Usually clear to yellow. As a general rule, The more yellow, the more concentrated. Some drugs (such as rifampin) will color urine (rifampin orange, for example), and abnormally colored urine will give false readings on the dipstick labs, which rely on color for their interpretation.

Clarity: Should be clear. UTI's lead to cloudy urine, because of cells or other particulate matter. Carbohydrates will also cloud a urine.

pH: Urine pH usually reflects serum pH, but with much greater variablility. Normal is anywhere from 5.0 to 9.0. Normally, if the serum is acidemic, the excess cations will be excreted in the urine, driving the pH down. Similarly, excess anions of alkalemia drive the urine pH up. Some conditions, however (such as renal tubular acidosis) demonstrate "paradoxical excretion," in which the kidney pathologically excretes anions even though there is no alkalemia - this results in a metabolic acidosis.
NOTE: If the pH is low (or if ascorbic acid [Vitamin C] is present in high quantities), this can lead to a FALSE NEGATIVE for nitrites - meaning that nitrites are really present, but they won't show up on the U/A.

Ketones: elevated in dehydration, fasting, or DKA (diabetic ketoacidosis - seen in Type I diabetics).

Hemoglobin (Hgb): if elevated,

Bilirubin: This refers to conjugated bilirubin (which is water-soluble - see LFT's page for details). Elevated in post- or intra- hepatic obstruction.

Urobilinogen: This is elevated in conditions with high unconjugated bilirubin, such as hemolysis or Gilbert's Disease.

Nitrites: This is elevated when bacteria (particularly Gram - organisms, generally fecal) are present in the urinary tract. The bugs that convert nitrate to nitrite are e. coli, enterobacter, citrobacter, klebsiella, and proteus. They take about 4 hours to do the conversion, so your best bet is a urine that's been waiting at least that long - such as a morning void. Many things can cause false negatives for nitrites, such as the presence of bugs other than those listed above, a lack of available nitrate to begin with (so nothing to convert), or all of the nitrite may be converted to nitrogen. Be sure to read the NOTE at the end of the pH paragraph, above.

Leukocyte Esterase: This enzyme is made by neutrophils as a response to the presence of bacteria. It indicates 2 things: [1] UTI; and [2] a functioning immune system. This will NOT rise in neutropenic patients, even if they have UTI's.

Glucose: Glucose spilling into the urine indicates a serum glucose of >180. People with normal kidneys and normal glucose metabolism do not have glucose in their urine (they may have 1+ immediately after a high carb meal).

Protein: The assays used in chemistry labs primarily detect albumin more than other proteins. These assays are not particularly good at detecting immunoglobulins, for example. If elevated, urinary protein indicates UTI, recent exercise or renal disease.
IMPORTANT: U/A protein is not sensitive enough for the microalbuminuria seen in diabetes. If you wish to detect/measure this, order the Urine Microalbumin Assay specifically.
IMPORTANT: If you suspect pre-ecplampsia or eclampsia, order a Total Urine Protein in addition to the U/A.

Specific Gravity: This is used to infer volume status, which you should be able to assess clinically with more accuracy than this test will provide. If spec grav is elevated, that means the urine is concentrated, suggesting a hypovolemia. If the spec grav is low, that means the urine is dilute, suggesting hypervolemia.
Optimally, U/A's will be collected first thing in the morning, when urine tends to be more concentrated. Spec grav goes up with high glucose or other elevated "stuff" in the urine. If you need a reading more accurate than 0.005 (sometimes needed in chemo patients), request analysis by refractometer, which is accurate down to 0.001. Be aware that contrast dye gives false high readings.

Casts: are associated with the collection of cells in the distal tubule, which become concretions after sufficient time has elapsed. They are generally associated with different conditions dependent on their color:
Red = nephritic syndrome.
White = pyelonephritis.
Muddy brown = renal failure.

Crystals: Seen in gout, kidney stones, or in the presence of many drugs.

Hardcore Urinalysis Secrets

This is the bonus points material in urinalysis interpretation - consider these interactions when interpreting particularly confusing findings. Beware that you earn geek points with this knowledge...

spec grav: Decreased readings in the presence of glucose or urea, compared with refractometry (glucose or urea will always raise spec grav). Increased readings with protein or ketoacidosis.

leukocyte esterase: The drugs cephalexin, gentamicin, and nitrofurantoin, &/or the presence of high albumin, may interfere with test results.

nitrite: Large amounts of ascorbic acid (vitamin C) decrease sensitivity. False positives possible with phenazopyridine, very basic urine (pH > 9.0), or when blood substitutes (polyvinylpyrrolidine) are used.

glucose: Vitamin C does NOT interfere with glucose readings in this hospital.

ketones: Phenylketone or phthalein compounds (used in liver and kidney function tests), or the use of MESNA, can interfere with interpretation

urobilinogen: False positives with phenazopyridine use. Decreased sensitivity with high nitrite &/or formalin concentrations.

bilirubin: Decreased sensitivity with vitamin C use, possibly in past 10 hours. Lower readings seen in presence of high nitrites. Large urobilinogen can falsely elevate this reading. False positives with phenazopyridine.

blood: Nitrite > 10 mg/dl delays reaction and can give false negative or low reading. Menstruating females can have false positives.