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White blood cell casts
4%
6/159
Fatty casts
1%
2/159
Muddy brown casts
86%
137/159
Hyaline casts
Broad waxy casts
7/159
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This patient's presentation is consistent with acute tubular necrosis (ATN). Muddy brown casts are part of the classic presentation of ATN. ATN is defined as acute suppression of renal function developing over 24 hours, and is caused by ischemic or toxic damage to the kidney. ATN is the most common cause of acute renal failure and is accompanied by anuria or oliguria. As a result of his myocardial infarction, this patient developed decreased cardiac output, resulting in ischemic ATN. Ischemic ATN manifests most commonly in the straight portion of the proximal tubule and in the thick ascending limb. This distribution of ischemic damage is due to the high metabolic activity of these tubular cells combined with the relatively low blood supply to the location of these tubular segments within the outer medulla. McDonald et al. describe the presence of casts (particularly RBC casts) in the urine and their diagnostic value. RBC casts can only be formed by glomerular bleeding. According to Gill et al., the recognition of urinary sediment in ATN, including muddy brown granular casts, should aid in the diagnosis of ATN. Illustration A is an example of muddy brown casts in a urine sample. Incorrect Answers: Answer 1: WBC casts are associated with acute pyelonephritis or acute tubulointersitial nephritis. Answer 2: Fatty casts are associated with nephrotic syndrome. Answer 4: Hyaline casts are non-specific with no diagnostic value. Answer 5: Waxy casts are associated with end stage renal disease.
4.8
(5)
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