Urine microscopy

Urine microscopy

Red blood cell morphology

Determined by phase-contrast microscopy. RBCs derived from the glomerulus are dysmorphic (they have been distorted by their passage through the glomerulus). RBCs derived from tubular bleeding (tubulointerstitial disease) and those from lower down the urinary tract (i.e. urological bleeding from the renal pelvis, ureters, or bladder) have a normal shape. Glomerular bleeding is suggested by the presence of dysmorphic RBCs, RBC casts, and proteinuria.

Casts

A protein coagulum (principally, Tamm Horsfall mucoprotein derived from tubular epithelial cells) formed in the renal tubule and cast in the shape of the tubule (i.e. long and thin). The protein matrix traps tubular luminal contents. If the cast contains only mucoproteins it is called a hyaline cast. Seen after exercise, heat exposure, and in pyelonephritis or chronic renal disease. Red blood cell casts contain trapped erythrocytes and are diagnostic of glomerular bleeding, most often due to glomerulonephritis. White blood cell casts are seen in acute glomerulonephritis, acute pyelonephritis, and acute tubulointerstitial nephritis.

Crystals

Specific crystal types may be seen in urine and help diagnose underlying problems (e.g. cystine crystals establish the diagnosis of cystinuria). Calcium oxalate, uric acid, and cystine are precipitated in acidic urine. Crystals precipitated in alkaline urine include calcium phosphate and triple-phosphate (struvite).