Urine Tests by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030291389
Publisher: Springer International Publishing

Hemoglobin

Hemoglobin (acellular casts that contain hemoglobin)

Associated with hemolytic anemia or renal parenchymal bleeding

May result from degradation of RBCs within a RBC cast (see Table 10.1)

Heme pigment has a direct renal tubulotoxic effect

Urinalysis will test positive for blood, but RBCs will be absent on urine microscopy (see Chap. 4)

Practical Clinical Use of Urinary Casts

The presence of urinary casts can trigger the clinician to specific diagnostic considerations in patient care. Given that prerenal AKI and ATN are the most common causes of AKI in hospitalized patients, differentiating between the two can be important in determining management.

Urine sediment is a useful tool to inform the diagnosis of ATN. Perazella et al. described a urinary sediment scoring system to distinguish ATN from prerenal AKI [7]. In patients with a high pretest probability of ATN, the presence of casts or rTEC inform a high positive predictive value and low negative predictive value for diagnosis of ATN. Conversely, in patient populations with a low pretest probability of ATN (e.g., prerenal AKI), a lack of casts or rTEC on urinary sediment lends a negative predictive value of 91%. Appropriate use of urine sediment in this case setting not only was a low-cost option to inform patient care but also prevented the patient from moving to an unneeded renal biopsy.

Similarly, a simplified acute kidney injury cast scoring index has been piloted to standardize urine microscopy and grade the degree (none, rare, moderate, sheets) of epithelial cell and granular casts present on urine microscopy. The scoring system was found to be reliable with good inter-observer agreement. The cast scoring index was then used to evaluate renal outcomes in patients with a clinical diagnosis of ATN. Patients without renal recovery had a higher cast scoring index as compared to patients who recovered kidney function [8].

Returning to case 3, the young female had both hyaline casts and granular casts on microscopic examination of the urine. The presence of many hyaline casts reflected poor renal perfusion likely from volume depletion. Her volume depletion was severe as the presence of granular casts reflected tubular injury. The granular casts were likely “muddy brown” in color signifying ATN. The serum creatinine in AKI due to mild to moderate ATN is usually noted to increase abruptly at first but then peak and level off followed by slow improvement. Severe ATN may require dialysis and have a prolonged recovery phase.

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