PHYSICAL
Color: Foods, medication, infection, or metabolic products can cause abnormal urine color.
- Red urine: Hematuria, hemoglobinuria, myoglobinuria, porphyria, beets, blackberries, rhubarb, rifampin
- Dark yellow to orange urine: Bile, phenothiazines, Pyridium
- Blue or green urine: Pseudomonas UTI, dyes from tests of kidney and bladder function, medications (amitriptyline, indomethacin, propofol, indigo carmine, cimetidine, promethazine, methylene blue, triamterene)
- Brown urine: Bile pigments, myoglobin, fava beans, levodopa, metronidazole, nitrofurantoin, senna
- Black urine: Alcaptonuria
- Dark brown or smoky urine suggests a renal source of hematuria.
- Pink or red urine suggests an extrarenal source.
Clarity: Cloudy or hazy urine may reflect the presence of phosphate crystals, pyuria, bacteria, chyluria, or lipiduria.
Odor: Can be influenced by diet, metabolic condition, or infection.
- Asparagus has a strong distinct order.
- Fruity or sweet odor may indicate diabetic ketoacidosis.
- Urinary tract infections may yield a a strong, pungent odor.
CHEMICAL / DIPSTICK
- Specific gravity correlates with urine osmolality. It reflects the relative degree of concentration or dilution of the specimen.
- pH reflects acid/base balance of body. Useful in diagnosis and management of urinary tract infections and calculi. Helpful in the diagnosis of distal renal tubular disease.
- Protein in the urine is a screen for nephrotic syndromes, including complications of diabetes mellitus, glomerulonephritis, amyloidosis, and other diseases. Proteinuria is the hallmark of renal disease.
- Glucose in the urine indicates hyperglycemia and the inability of the proximal tubule to absorb any more glucose - as seen in diabetes mellitus.
- Occult blood is a screen for hemoglobin, myoglobin, or red blood cells in the urine.
- Ketones are products of fat metabolism and not normally seen in urine. Ketonuria can occur in infants and children with febrile illnesses or toxic states with marked vomiting or diarrhea. It may be noted in normal pregnancy, starvation, high protein diet, eclampsia thyrotoxicosis, and isopropanol ingestion.
- Leukocyte esterase is produced by neutrophils and may indicate pyuria associated with inflammation or UTI
- Nitrite is formed when bacteria present in the urine reduce nitrates to nitrates. Many gram-negative and some gram-positive organisms are capable of this conversion. A positive nitrate is indicative of a UTI.
- Bilirubin - detect conjugated (water-soluble) bilirubin in urine which is indicative of liver disease or biliary obstruction.
- Urobilinogen is a product of bilirubin reduction. It is formed in the intestine. A portion of this is excreted in feces and some is resorbed and excreted in the urine. Decreased urine levels are seen in biliary obstruction and treatment with broad-spectrum antibiotics. Increased urine levels are seen in hemolytic diseases and liver dysfunction.
MICROSCOPY:
Cells:
- White cells (leukocyturia) may indicate inflammatory disease in the genitourinary tract, including bacterial infection, glomerulonephritis, chemical injury, autoimmune diseases, or inflammatory disease adjacent to the urinary tract such as appendicitis or diverticulitis. Pyuria predominating in the urinary sediment in renal failure is found (even without superimposed usual bacterial infection) with analgesic abuse nephropathy, renal tuberculosis, and polycystic kidney disease.
- Red cells (hematuria) in the urine may indicate kidney stone, kidney injury, infection, or glomerulonephritis. “Dysmorphic” red cells (heterogeneous sizes, hypochromia, distorted irregular outlines and frequently small blebs extruding from the cell membrane) are observed in glomerulonephritis.
Epithelial cells:
- Squamous cells indicate contamination, poor clean-catch collection.
- Transitional cells are typically present due to normal sloughing of epithelia.
- Renal cells may indicate renal pathology.
Casts
- Hyaline casts occur in physiologic states (eg, after exercise) and many types of renal diseases. They are best seen in phase contrast microscopy or with reduced illumination.
- White cell casts indicate the renal origin of leukocytes, and are most frequently found in acute pyelonephritis. White cell casts are also found in glomerulonephritis such as lupus nephritis, and in acute and chronic interstitial nephritis. When nuclei degenerate, such leukocyte casts resemble renal tubular casts.
- Red cell casts indicate renal origin of hematuria and suggest glomerulonephritis. Red cell casts may also be found in subacute bacterial endocarditis, renal infarct, vasculitis, Goodpasture syndrome, sickle cell disease, and in malignant hypertension. Degenerated red cell casts may be called “hemoglobin casts”. Orange to red casts may be found with myoglobinuria as well.
- Renal tubular (epithelial) casts are most suggestive of tubular injury, as in acute tubular necrosis. They are also found in other disorders, including eclampsia, heavy metal poisoning, ethylene glycol intoxication, and acute allograft rejection.
- Granular casts are very finely granulated casts that may be found after exercise and in a variety of glomerular and tubulointerstitial diseases. Coarse granular casts are abnormal and are present in a wide variety of renal diseases. “Dirty brown” granular casts are typical of acute tubular necrosis.
- Waxy casts are found especially in chronic renal diseases and are associated with chronic renal failure; they occur in diabetic nephropathy, malignant hypertension, and glomerulonephritis, among other conditions. They are named for their waxy or glossy appearance. They often appear brittle and cracked.
- Fatty casts and oval fat bodies (“lipiduria”) are generally found in the nephrotic syndromes, usually glomerular diseases including minimal change disease, focal segmental glomerulosclerosis, membranous glomerulopathy, and membranoproliferative glomerulonephritis. Nephrotic range proteinuria is also found in multisystem diseases including amyloidosis, SLE, cryoglobulinemia, and diabetic nephropathy. Fat droplets originate in renal tubular cells when they exceed their capacity to reabsorb protein of glomerular origin. Fat, Urine and Protein, Quantitative, Urine, 24-Hour.
- Broad casts originate from dilated, chronically damaged tubules or the collecting ducts. They can be granular or waxy. Broad waxy casts are called “renal failure casts.”
Crystals:
Crystalluria is frequently observed in urine specimens stored at room temperature or refrigerated. The crystals form as the urine temperature drops (in vitro crystal formation). Crystals are most diagnostically useful when observed in warm, fresh urine (in vivo crystal formation) in evaluation of hematuria, nephrolithiasis, or toxin ingestion. Polarizing microscopy and pH are useful in crystal identification.
- Calcium oxalate crystals classically appear as a refractile square envelope shapes that can vary in size; ovoid and dumbbell shapes of oxalate crystals are less commonly seen.
- Calcium oxalate and/or hippurate crystals, in abundance, may suggest ethylene glycol ingestion (especially if known to be accompanied by neurological abnormalities, appearance of drunkenness, hypertension, and a high anion gap acidosis).
- Uric acid crystals are reddish brown, rectangular, rhomboidal, or flower-like structures of narrow rectangular petals. Ammonium urates, in alkaline urine, are irregular blobs and crescents, sometimes resembling fragmented red cell shapes.
- Cystine crystals, uniquely in urine, form large irregular hexagonal plates. They are present in acidic urine and may dissolve if alkalinized. They occur only in the urine of subjects with cystinuria (see Cystine, Urine).
- Tyrosine crystals, rarely seen, are found in acidic urine and appear as fine silky needles arranged in bundles. Products of protein metabolism, they appear in urine of people with tissue degeneration or necrosis; usually seen with leucine crystals.
- Calcium phosphate crystallizes in urine as flowers of narrow rectangular needles. Found in alkaline urine.
- Calcium magnesium ammonium phosphate, or “triple phosphate,” (struvite crystals) forms unique “coffin lid” angularly domed rectangles which may be present in massive quantities in alkaline urine. They usually are associated with urine infected by urea-splitting bacteria which cause “infection,” or “triple phosphate” stones.
- Indinavir crystals are found in >30% of patients treated with this protease inhibitor. Manual microscopy detects such radial clusters, forming starburst shapes (Horton, 2000; Trainor, 1998).
Bacteria present in a female urine specimen may indicate vaginal contamination or true infection. Discerning the difference is based on number of bacteria (or colony-forming units/mL urine - CFUs/mL) seen per high-powered field (HPF) and symptoms. However, asymptomatic urinary tract infections are often detected on the microscopic exam. The presence of bacteria in a properly collected male urine specimen is suggestive of infection and culture should be considered.
Spermatozoa may be seen in male urine related to recent or retrograde ejaculation. In female urine, the presence of spermatozoa may provide evidence of vaginal contamination following recent intercourse. Presence of sperm is not typically reported in routine urinalysis exams.