What does the presence of Red Blood Cell (RBC) casts in urine indicate?

From the Guidelines

The presence of red blood cell (RBC) casts in urine is a definitive indicator of glomerular disease, such as acute glomerulonephritis, and warrants immediate nephrology consultation and further evaluation. RBC casts form when red blood cells leak through damaged glomerular membranes and become trapped in the protein matrix of tubular casts, localizing the bleeding to the glomeruli rather than elsewhere in the urinary tract [ 1 ]. The underlying pathophysiology involves immune complex deposition or direct antibody attack on the glomerular basement membrane, leading to inflammation and subsequent damage that allows red blood cells to enter the tubular system where they form casts.

Common causes of acute glomerulonephritis include post-streptococcal glomerulonephritis, lupus nephritis, IgA nephropathy, and vasculitis. When RBC casts are detected, additional testing such as serum creatinine, BUN, complete urinalysis, urine protein quantification, and possibly serologic studies for autoimmune conditions is typically warranted [ 1 ]. The presence of RBC casts often correlates with other urinary abnormalities including proteinuria and hematuria.

Some key points to consider in the evaluation of RBC casts in urine include:

• The presence of significant proteinuria, red cell casts, or renal insufficiency should prompt an evaluation for renal parenchymal disease or referral to a nephrologist [ 1 ].
• Dysmorphic urinary red blood cells show variation in size and shape and usually have an irregular or distorted outline, and are generally glomerular in origin [ 1 ].
• Accurate determination of red blood cell morphology may require inverted phase contrast microscopy [ 1 ].
• Patients with proteinuria, dysmorphic RBCs, cellular casts, or renal insufficiency may have medical renal disease, which can cause hematuria, and should be referred to a nephrologist [ 1 ].

Overall, the detection of RBC casts in urine is a significant finding that requires prompt evaluation and consultation with a nephrologist to determine the underlying cause and guide further management.

From the Research

Presence of RBC Casts in Urine

The presence of Red Blood Cell (RBC) casts in urine is a significant indicator of certain renal diseases.

• RBC casts are formed in the renal tubules and are typically seen in patients with glomerulonephritis, a type of kidney disease that involves inflammation of the glomeruli 2, 3.
• The presence of RBC casts in urine can also be seen in other conditions such as diabetic nephropathy, although it is less common 3.
• RBC casts can be identified using various methodologies, including the standard method and concentration technique, with the latter showing a higher rate of RBC cast identification 4.

Clinical Significance

The clinical significance of RBC casts in urine includes:

• Indicating glomerular bleeding source and glomerular hematuria 2, 4
• Being a strong indicator of renal disease, particularly glomerulonephritis 2, 3
• Correlating with the severity of histologic features and renal dysfunction in patients with infection-related glomerulonephritis 5
• Being associated with worse renal dysfunction and higher percentages of cellular crescent in patients with infection-related glomerulonephritis 5

Other Conditions

RBC casts can also be seen in other conditions, including:

• Acute interstitial nephritis, a type of kidney disease that involves inflammation of the tubules and interstitium 6
• Diabetic nephropathy, although it is less common 3
• Infection-related glomerulonephritis, where RBC casts are associated with worse renal dysfunction 5