What are the implications of finding casts in the urine?

From the Guidelines

Casts in urine are a significant finding that requires prompt medical evaluation, as they can indicate various kidney conditions, and the presence of red cell casts, in particular, is virtually pathognomonic for glomerular bleeding 1. When found during urinalysis, casts can suggest kidney damage or disease, and their types can provide valuable diagnostic information. The most common types include:

• Hyaline casts, which are generally benign and may appear with fever, exercise, or dehydration
• Granular casts, suggesting tubular damage
• Red blood cell casts, indicating glomerulonephritis
• White blood cell casts, suggesting kidney infection or inflammation
• Waxy casts, associated with chronic kidney disease If casts are detected in your urine, you should consult a healthcare provider promptly for further assessment, which typically includes additional urine tests, blood work to check kidney function, and possibly imaging studies, as recommended by the AUA/SUFU guideline 1. Treatment depends entirely on the underlying cause, ranging from simple hydration for hyaline casts associated with dehydration to antibiotics for infection-related casts or immunosuppressive medications for inflammatory conditions. The presence of significant proteinuria, red cell casts, or renal insufficiency should prompt an evaluation for renal parenchymal disease or referral to a nephrologist, as these findings can indicate medical renal disease 1. In patients with microhematuria, risk-based urologic evaluation should still be performed, even if medical renal disease is suspected, to identify coexistent urologic pathology 1.

From the FDA Drug Label

Crystals of ciprofloxacin have been observed rarely in the urine of human subjects but more frequently in the urine of laboratory animals, which is usually alkaline. Crystalluria related to ciprofloxacin has been reported only rarely in humans because human urine is usually acidic.

Casts in urine are not directly mentioned in the provided drug labels. However, crystalluria, which refers to the presence of crystals in the urine, is discussed.

• Crystalluria is more common in laboratory animals due to the alkaline nature of their urine.
• In humans, crystalluria is rare because human urine is typically acidic.
• To minimize the risk of crystalluria, patients should be well hydrated to prevent the formation of highly concentrated urine, and alkalinity of the urine should be avoided 2.

From the Research

Casts in Urine

• Casts in urine can imply underlying pathogenesis and diagnosis, with waxy casts being a specific type that is poorly understood 3
• The detection rate of waxy casts in urine sediment was found to be 26.3% in a study of 1282 patients 3
• Waxy casts are closely related to impaired renal function, with their presence being a specific indicator of renal insufficiency, but not sensitive enough 3
• The presence of waxy or pre-waxy casts in urine is associated with higher blood pressure, more proteinuria, and worse renal function 3
• Urinalysis, which includes the examination of urine sediment for casts, is a widely used diagnostic tool to assist clinicians in determining the etiology of various acute or chronic pathologies 4

Clinical Correlations

• Waxy or pre-waxy casts are independently associated with eGFR, proteinuria, and pathological lesions, indicating their potential use as a diagnostic marker for renal insufficiency 3
• The sensitivity and specificity of waxy casts as a diagnostic marker for renal insufficiency were found to be 0.29 and 0.97, respectively, while the sensitivity and specificity of waxy or pre-waxy casts were 0.58 and 0.88, respectively 3
• Urinalysis can provide valuable information about the underlying causes of renal disease, and the interpretation of urine sediment findings, including casts, is essential for accurate diagnosis and treatment 4

Limitations

• There is limited research on the clinical significance of casts in urine, particularly waxy casts, and further studies are needed to fully understand their role in diagnosis and treatment 3
• The study on waxy casts in urine had a large sample size, but the results may not be generalizable to all populations, and further research is needed to confirm the findings 3