Renal Pathophysiology

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction

213

in which cast formation is likely to occur, a process that has been likened to the setting of gelatin. Casts generally form in the collecting tubules, the site at which the urine is most concentrated and most acidic. Urinary stasis, as in poorly functioning nephrons with low flow, also promotes cast formation. When the lumen is free of cells, the cast will be composed almost entirely of matrix. These casts are called hyaline casts and are of no diagnostic signifi cance. However, cellular casts can occur if there are cells (white cells, red cells, epithelial cells) in the lumen as THMP precipitates. This finding is important clinically because it identifies the kidney as the source of the cells (see Table 8.2). For example, white cells can enter the urine at any site in the urinary tract, from the kidney to the bladder to the urethra. However, the presence of casts con taining white cells (called white cell casts ) indicates inflammation in the kidney.

TABLE 8.2. Correlation Between Characteristic Urinary Findings and Some Major Causes of Acute and Chronic Renal Disease

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction

Urinary Findings

Etiology

Proteinuria ( > 3.5 g/day) and lipiduria Proteinuria ( < 3.5 g/day) with dysmorphic red blood cells and red blood cell casts (of ten with white blood cells as well) Proteinuria ( < 1 g/day)

Nephrotic syndrome; diagnostic of glomeru lar disease (see Chapter 9) Nephritic syndrome; often seen with glomer ulonephritis and vasculitis. There can be a significant overlap of these two syndromes (see Chapter 9). Can be seen with tubulointerstitial disease, vascular disease, hypertension, and from many etiologies resulting in advanced chronic kidney disease Seen in acute renal failure and suggestive of acute tubular necrosis. However, some patients with this disorder lack these findings and have a relatively normal urinalysis Suggestive of some form of tubulointerstitial disease or obstruction. Can be seen with acute interstitial nephritis, a disorder in which eosinophiluria may be seen. Can also occur with urinary tract infection due to common bacteria or tuberculosis Acute : may be found in prerenal disease, urinary tract obstruction, and tubular diseases such as hypercalcemia, multiple myeloma, a or in some cases of acute tubular necrosis Chronic : may be seen in prerenal disease, urinary tract obstruction, benign hypertensive nephrosclerosis, and tubular or interstitial diseases

Renal tubular epithelial cells with granular and epithelial cell casts

Pyuria with white cell and granular casts with no or mild proteinuria ( < 1.5 g/day) and variable hematuria

Normal or near normal—few cells with few or no casts and little or no proteinuria; hyaline casts are not an ab normal finding.

Copyright © 2023 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited.

a The urinalysis is typically negative in myeloma kidney because the dipstick detects albumin, but not the immunoglobulin light chains responsible for the disease both by precipitating and obstructing nephrons and by directly damaging the tubular cells (see Chapter 10).