Renal Pathophysiology

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction

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Urinalysis Analysis of the urine should be performed on a fresh specimen within 30 to 60 minutes after voiding. A midstream specimen is adequate after first cleans ing the external genitalia to avoid contamination with local secretions. The stage in the menstrual cycle should also be noted because active menses can lead to blood contamination of the urine sample. The fresh urine should be assessed by dipstick and then centrifuged at 3,000 rpm/min for 3 to 5 minutes. Most of the supernatant should then be poured into a separate tube, and the sediment at the bottom of the tube B. Vascular disease 1. Benign or malignant hypertensive nephrosclerosis 2. Systemic vasculitis 3. Thrombotic microangiopathy in the hemolytic-uremic syndrome, thrombotic thrombocytopenic purpura, and scleroderma C. Tubular disease 1. Acute tubular necrosis 2. Myeloma kidney 3. Hypercalcemia (also causes afferent vasoconstriction) 4. Polycystic kidney disease 5. Interstitial nephritis a. Acute, usually drug-induced interstitial nephritis b. Acute pyelonephritis (infection of the renal parenchyma) c. Chronic pyelonephritis, usually due to vesicoureteral reflux d. Analgesic nephropathy, lithium nephropathy TABLE 8.1. Most Common Causes of Renal Disease I. Postrenal—urinary tract obstruction; need to exclude early in the evaluation A. Prostatic disease B. Pelvic or retroperitoneal adenopathy or malignancy C. Renal or ureteric calculi (bilateral) D. Congenital abnormalities II. Prerenal A. Volume depletion caused by gastrointestinal, renal, skin, or third space losses B. Congestive heart failure or valvular abnormalities in which there is a primary reduction in cardiac output C. Hepatic cirrhosis in which splanchnic vasodilation leads to pooling in the splanchnic system and underperfusion of other organs D. Nonsteroidal anti-inflammatory drugs, which can induce vasocon striction in susceptible subjects by blocking the synthesis of renal vasodilator prostaglandins E. Bilateral renal artery stenosis, often made worse by the use of an angiotensin-converting enzyme inhibitor that interferes with auto regulation of the glomerular filtration rate F. Shock due to sepsis, fluid loss, or cardiac disease III. Intrinsic disease A. Glomerular disease 1. Glomerulonephritis 2. Nephrotic syndrome

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction

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