What do small protein and red blood cell casts in urine indicate?

From the Guidelines

The presence of small protein and red blood cell casts in urine is a strong indicator of glomerular disease, such as acute glomerulonephritis, and requires prompt medical evaluation by a nephrologist or primary care physician. This finding suggests inflammation of the kidney's glomeruli and potential damage to the glomerular filtration barrier, as indicated by the presence of proteinuria 1. According to the KDIGO 2021 clinical practice guideline for the management of glomerular diseases, routine evaluation of urine sediment for erythrocyte morphology and the presence of red cell casts and/or acanthocytes is indicated in all forms of glomerular disease 1.

Key Considerations

• The presence of red blood cell casts and proteinuria in urine suggests glomerular bleeding or proteinuria, which should prompt an evaluation for renal parenchymal disease 1.
• Patients with microscopic hematuria, a negative initial urologic evaluation, and no evidence of glomerular bleeding are considered to have isolated hematuria, but still require follow-up for the development of hypertension, renal insufficiency, or proteinuria 1.
• Common causes of glomerulonephritis include post-streptococcal glomerulonephritis, lupus nephritis, IgA nephropathy, and vasculitis, each requiring different treatment approaches.

Recommendations

• Patients should provide a complete medical history and undergo additional testing, including comprehensive urinalysis, blood tests for kidney function, and possibly kidney imaging or biopsy.
• While awaiting medical care, patients should monitor their blood pressure, maintain adequate hydration without overhydrating, and avoid nephrotoxic medications like NSAIDs.
• Monitoring of hematuria (magnitude and persistence) may have prognostic value in many forms of glomerular disease, particularly in immunoglobulin A nephropathy (IgAN) and vasculitis (IgAV) 1.

From the Research

Urine Casts and Kidney Disease

• Small protein and red blood cell casts in urine can be indicative of kidney disease, as they suggest damage to the glomeruli or other parts of the kidney 2, 3.
• The presence of these casts can be detected through examination of urinary sediment, which is a technique used to evaluate patients with chronic kidney disease 2.
• Urine dipstick testing for red and white blood cells can also help determine the underlying cause of chronic kidney disease 2.

Detection and Staging of Kidney Disease

• Laboratory measurements, such as glomerular filtration rate (GFR) and albuminuria, are required for the detection and staging of acute and chronic kidney disease in adults 3.
• The Kidney Disease Improving Global Outcomes (KDIGO) guidelines define and stage acute and chronic kidney diseases by GFR and albuminuria 3.
• Accurate diagnosis, classification, and risk stratification for chronic kidney disease allow for early recognition and delivery of optimal care 4.

Limitations of Diagnostic Tools

• Creatinine-based GFR has limitations, including non-GFR determinants such as muscle mass, diet, and tubular handling 4.
• Cystatin C can be used as an alternative or additional endogenous filtration marker, but its role is limited due to concerns regarding false positive results 4.
• The kidney failure risk equation (KFRE) has been developed to help determine the risk of progression to end-stage kidney disease, but its performance in ethnic minority groups and certain kidney diseases remains modest 4.