Renal Pathophysiology

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RENAL PATHOPHYSIOLOGY: THE ESSENTIALS

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Normal Urine Sediment In addition to a small amount of protein, normal urine contains up to 1 million red cells, 3 million white and epithelial cells, and 10,000 casts (almost all hyaline) per day. When a random urine specimen is examined, these obser vations translate into 0 to 4 white cells and 0 to 2 red cells per high-power field. Occasional calcium oxalate, uric acid, or phosphate crystals also may be seen, depending on the urine pH. Although the excretion of more protein, cells, or casts may be indicative of underlying renal disease, it is important to appreciate that a variety of con ditions (including extreme exercise and fever) can induce transient changes „ PLATE 8.3. Crystals in the urine sediment. A. Uric acid crystals are yellow or reddish-brown and are seen only in urine with an acid pH. These crystals are pleo morphic, most often appearing as rhombic plates or rosettes. B. Calcium oxalate crystals with the characteristic “envelope” appearance; these crystals may also as sume a dumbbell shape. C. “Coffin-lid” ammonium magnesium phosphate crystals form only in urine with alkaline pH. D. Cystine crystals have a characteristic hexag onal shape.

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