Kidney disease can be discovered incidentally during a routine medical evaluation or with evidence of kidney dysfunction, such as hypertension, edema, nausea, or hematuria. The initial approach in both situations should be to assess the cause and severity of renal abnormalities. In all cases, this evaluation includes (1) an estimation of disease duration, (2) a careful urinalysis, and (3) an assessment of the glomerular filtration rate (GFR). The history and physical examinations, though equally important, are variable among renal syndromes—thus, specific symptoms and signs are discussed under each disease entity.
ASSESSMENT OF KIDNEY DISEASE
Kidney disease may be acute or chronic. Acute kidney injury is worsening of kidney function over hours to days, resulting in the retention of nitrogenous wastes (such as urea nitrogen) and creatinine in the blood. Retention of these substances is called azotemia. Chronic kidney disease (CKD) results from an abnormal loss of kidney function over months to years. Differentiating between the two is important for diagnosis, treatment, and outcome. Oliguria is unusual in CKD. Anemia (from low kidney erythropoietin production) is rare in the initial period of acute kidney injury. Small kidneys are most consistent with CKD, whereas normal to large-size kidneys can be seen with both chronic and acute disease.
A urinalysis can provide information similar to a kidney biopsy in a way that is cost-effective and noninvasive. The urine is collected in midstream or, if that is not feasible, by bladder catheterization. The urine should be examined within 1 hour after collection to avoid destruction of formed elements. Urinalysis includes a dipstick examination followed by microscopic assessment if the dipstick has positive findings. The dipstick examination measures urinary pH, protein, hemoglobin, glucose, ketones, bilirubin, nitrites, and leukocyte esterase. Urinary specific gravity is often reported. Microscopy provides examination of formed elements—crystals, cells, casts, and infecting organisms.
Various findings on the urinalysis are indicative of certain patterns of kidney disease. A bland (normal) urinary sediment is common, especially in CKD and acute disorders that are not intrinsic to the kidney, such as limited effective blood flow to the kidney or obstruction of the urinary outflow tract. Casts are composed of Tamm-Horsfall urinary mucoprotein in the shape of the nephron segment where they were formed. Heavy proteinuria and lipiduria are consistent with the nephrotic syndrome. The presence of hematuria with dysmorphic red blood cells, red blood cell casts (eFigure 22–1), and proteinuria is indicative of glomerulonephritis. Dysmorphic red blood cells are misshapen during abnormal passage from the capillary through the glomerular basement membrane (GBM) into the urinary space of the Bowman capsule. Pigmented granular casts (also termed “muddy brown casts”) and renal tubular epithelial cells alone or in casts suggest acute tubular necrosis. White blood cells, including neutrophils and eosinophils, white blood cell casts (Table 22–1), red blood cells, and small ...