What does the presence of amorphous crystals and Red Blood Cells (RBCs) in urine indicate?

Evaluation and Management of Amorphous Crystals and RBCs in Urine

The presence of amorphous crystals and red blood cells (RBCs) in urine requires a comprehensive urologic and nephrologic evaluation as it may indicate underlying renal parenchymal disease, urinary tract malignancy, or other conditions that would benefit from intervention. 1

Clinical Significance of Findings

• Amorphous crystals (commonly urates or phosphates) are frequently found in urine and are often a normal finding related to urine concentration, pH changes, or dietary factors, but they can sometimes obscure other significant findings during routine urinalysis 2, 3
• The presence of RBCs alongside crystals requires careful evaluation, as persistent microscopic hematuria warrants investigation for potential urologic or nephrologic conditions 1
• When amorphous crystals and RBCs are found together, it's essential to determine if the RBCs are dysmorphic (suggesting glomerular origin) or isomorphic (suggesting lower urinary tract origin) 4

Initial Diagnostic Approach

• Repeat urinalysis after 48 hours if a benign cause is suspected (e.g., after vigorous exercise, sexual activity, menstruation) to confirm persistence of findings 1
• Assess for dysmorphic RBCs, which strongly suggest glomerular disease - dysmorphic RBCs accounting for >75% of total RBCs indicate renal hematuria, while <17% suggests non-renal hematuria 4
• Evaluate for proteinuria, as the combination of hematuria and proteinuria significantly increases the likelihood of primary renal disease 5
• Check for cellular casts, which are highly specific for glomerular or tubulointerstitial kidney disease 5
• Obtain renal function tests including serum creatinine, estimated GFR, and BUN to assess for renal dysfunction 1

Nephrologic Evaluation

• The presence of dysmorphic RBCs, proteinuria, cellular casts, or renal insufficiency warrants concurrent nephrologic work-up but does not preclude urologic evaluation 1, 5
• Quantify proteinuria with a 24-hour urine collection if dipstick shows ≥1+ proteinuria 5, 6
• Evaluate for systemic diseases associated with glomerulonephritis, including lupus erythematosus, vasculitis, and infections 5
• Consider renal biopsy when systemic causes are not identified in patients with findings suggestive of glomerular disease 5

Urologic Evaluation

• Cystoscopy should be performed on all patients aged 35 years and older with asymptomatic microhematuria 1
• For patients younger than 35 years, cystoscopy may be performed at the physician's discretion based on risk factors 1
• Upper urinary tract imaging (IVU, ultrasonography, or CT) should be performed to detect potential urologic causes such as renal cell carcinoma, transitional cell carcinoma, urolithiasis, or renal infection 1
• Voided urinary cytology is recommended in patients who have risk factors for transitional cell carcinoma 1

Special Considerations

• Patients taking anticoagulants still require complete urologic and nephrologic evaluation regardless of the type or level of anticoagulation therapy 1
• Amorphous urate crystals can be dissolved by prewarming the urine specimen to 60°C for 90 seconds to enhance visibility of other elements 2
• Do not attribute hematuria solely to anticoagulation therapy when cellular casts and significant proteinuria are present, as these findings suggest intrinsic renal disease 5

Follow-up Recommendations

• If initial evaluations are negative, yearly urinalyses should be conducted to monitor for changes 7
• Long-term monitoring should include blood pressure checks and assessment for proteinuria at 6,12,24, and 36 months 6, 7
• Patients with isolated findings and normal renal function should be monitored for development of hypertension, increasing proteinuria, and declining renal function 6