DESCRIPTIONS OF MICROSCOPIC ELEMENTS
a diagram of cast formation
Hyaline casts are formed in the absence of cells in the renal tubular lumen. They have a smooth texture and a refractive index very close to that of the surrounding fluid. When present in lower numbers (0-1/LPF) in concentrated urine of otherwise normal patients, hyaline casts are not always indicative of clinically significant disease. Greater numbers of hyaline casts may be seen associated with proteinuria of renal (eg., glomerular disease) or extra-renal (eg., overflow proteinuria as in myeloma) origin.
Fatty casts are identified by the presence of refractile lipid droplets. The background matrix of the cast may be hyaline or granular. Often, they are seen in urines in which free lipid droplets are present as well. Interpretation of the significance of fatty casts should be based on the character of the cast matrix, rather than on the lipid content. Pictured is a fatty cast with a hyaline matrix. As an isolated finding, lipiduria is seldom of clinical significance.
Waxy casts have a smooth consistency but are more refractile and therefore easier to see compared to hyaline casts. They commonly have squared off ends, as if brittle and easily broken.
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
Oval Fat Bodies (OFB) are similar in composition and significance to fatty casts.
Calcium Oxalate Dihydrate crystals typically are seen as colorless squares whose corners are connected by intersecting lines (resembling an envelope). They can occur in urine of any pH. The crystals vary in size from quite large to very small. Dietary asparagus and ethylene glycol intoxication are notorious for urinary calcium oxalate formation.
Amorphous crystals appear as aggregates of finely granular material without any defining shape. Amorphous urates of Na, K, Mg or Ca tend to form in acidic urine and may have a yellow or yellow-brown color. Amorphous phosphates are similar in general appearance, but tend to form in alkaline urine and lack color. Generally, no specific clinical interpretation can be made for the presence of amorphous crystals.
Triple phosphate (Struvite, Magnesium Ammonium Phosphate) crystals usually appear as colorless, prism-like "coffin lids". They are often seen in urine from clinically normal individuals. Although they can be found in urine of any pH, their formation is favored in neutral to alkaline urine. Urinary tract infection with urease producing bacteria (eg. Proteus vulgaris) can promote struvite crystalluria (and urolithiasis) by raising urine pH and increasing free ammonia.
Uric acid crystals may appear as yellow to brown rhombic or hexagonal plates, needles or rosettes. With rare exceptions, the finding of uric acid crystals in urine is of little clinical value.
Trichomonas vaginalis is a sexually-transmitted urogenital parasite of men and women. The organism varies in size between 1-2 times the diameter of WBC. The organism is readily identified by its rapid erratic "jerky" movement.
