Renal Pathophysiology



„ PLATE 8.2. Red and white cells in the urine sediment ( left panel ). White cells are about twofold larger and have a granular cytoplasm and multilobed nucleus ( red arrows ). Red blood cells are smaller and have no nucleus. For comparison ( right panel ), dysmorphic red blood cells were seen in a patient with acute glomerulone phritis. Note the abnormal blebbing, irregular shape, and varied sizes that result from red blood cells traversing the glomerular basement membrane and from pas saging through the hypertonic medullary interstitium. A 27-year old male with a history of intravenous drug abuse is found unresponsive and brought to the emergency department. He is noted to have a creatinine of 10 mg/dL (no previous baseline available), and urinalysis is notable for 3 + blood but only rare red blood cells. Renal ultrasound was normal. What is the differential diagnosis for renal failure that accounts for the discrepancy between the dipstick and urine sediment? White Cells White cells are larger than red cells (about twofold) and can be identified by their granular cytoplasm. Neutrophils will have multilobed nuclei, but lym phocytes have uniform nuclei. Urinary white cells (pyuria) are usually indica tive of infection or inflammation at some site in the urinary tract. White cell casts locate the lesion to the kidney as with acute pyelonephritis (an infection of the renal parenchyma) or a tubulointerstitial disease such as acute inter stitial nephritis (see Chapter 11). Pyuria can also be seen with glomerular inflammation, but hematuria and proteinuria are usually more prominent in this setting. Neutrophils are usually the predominant white cell in the urine. How ever, other white cells can be seen, with eosinophils having the greatest potential diagnostic significance. Eosinophiluria is a frequent finding in al lergic, generally drug-induced acute interstitial nephritis, although it is not 2

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