MICROSCOPY:
Crystalluria
is frequently observed in urine specimens stored at room temperature or
refrigerated. Such crystals are diagnostically useful when observed in
warm, fresh urine by a physician evaluating microhematuria,
nephrolithiasis, or toxin ingestion.
In abundance, calcium oxalate and/or hippurate crystals
may suggest ethylene glycol ingestion (especially if known to be
accompanied by neurological abnormalities, appearance of drunkenness,
hypertension, and a high anion gap acidosis). Large numbers of calcium
oxalate crystals occur, as well, with acute renal failure following
methoxyflurane anesthesia. Urine is usually supersaturated in calcium
oxalate, often in calcium phosphate, and acid urine is often saturated
in uric acid. Yet crystalluria is uncommon (in warm, fresh urine)
because of the normal presence of crystal inhibitors, the lack of
available nidus, and the time factor. When properly observed in fresh
urine, crystals may provide a clue to the composition of renal stones
even not yet passed, the nidus for such stones, or, as such, have been
associated with microhematuria.
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
appendicitis1 or diverticulitis.
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,
including lupus nephritis. 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.
Hyaline casts occur in physiologic states (eg, after exercise) and many types of renal diseases.
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:
Very finely granulated casts 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 are found in the nephrotic
syndromes generally, diabetic nephropathy, other forms of chronic renal
diseases, and glomerulonephritis. The fat droplets originate in renal
tubular cells when they exceed their capacity to reabsorb protein of
glomerular origin. Their inclusions have the features and significance
of oval fat bodies.
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.”
Sperm is not reported in routine urinalysis exams. Spermatozoa may be seen in male urine related to recent or retrograde ejaculation. For sperm reporting in males only, order Postejaculatory Urine Microscopic Examination for Sperm [133116].
