Amorphous Cells in Urine: Identification and Clinical Significance
Amorphous cells in urine are not actually cells but rather precipitated crystals or salts that appear as small, granular particles without distinct cellular structure, commonly forming in concentrated or acidic urine. 1
Types and Composition of Amorphous Material
- Amorphous urates are the most common type, appearing in approximately 7.9% of urine samples with crystalluria, typically forming in acidic urine (pH < 7.0) 2
- Amorphous phosphates are another common form, usually precipitating in alkaline urine (pH > 7.0) 3
- These precipitates are part of the inorganic component of urinary sediment, distinct from cellular elements like epithelial cells, red blood cells, or white blood cells 4
- They appear as small, granular clumps without defined cellular structure when viewed under microscopy 1
Clinical Significance
- Amorphous material in urine is generally considered a normal finding and rarely indicates pathology 3
- The presence of amorphous crystals can obscure other significant findings during routine urinalysis, potentially hiding important elements like bacteria, yeast, or cellular components 1
- Unlike dysmorphic red blood cells (particularly acanthocytes) which indicate glomerular bleeding, amorphous material has no specific diagnostic value for kidney disease 5
- Amorphous urates typically form in concentrated urine with acidic pH, which can occur with normal physiological variations 1
Handling Amorphous Material in Laboratory Analysis
- When amorphous material interferes with urinalysis interpretation, prewarming the urine specimen to 60°C for 90 seconds can dissolve most amorphous urates without damaging other cellular elements 1
- Addition of 50 mM sodium hydroxide (NaOH) to the sediment can dissolve amorphous urates to enhance visibility of bacteria and yeast, but this damages white blood cells and red blood cells 1
- Proper identification may require specialized techniques like Fourier transform infrared microspectroscopy (FTIRM) in unusual cases 2
- Most amorphous material can be identified through a combined approach using knowledge of crystal morphology, birefringence features, and urine pH 2
Differentiation from Other Urinary Elements
- Amorphous material should be distinguished from actual cellular elements like squamous epithelial cells, which originate from the urethra, bladder trigone, or external contamination 6
- Unlike extracellular vesicles (EVs) which have a phospholipid bilayer structure and specific cellular origins, amorphous material consists of precipitated salts without biological membrane structure 7
- Proper microscopic examination can differentiate amorphous precipitates from dysmorphic red blood cells, which have diagnostic significance for glomerular disease 5
When to Consider Further Evaluation
- Persistent, heavy crystalluria (not just amorphous material) may warrant evaluation for conditions like urolithiasis, especially if accompanied by symptoms 4
- The presence of specific crystal types (like cystine or certain drug crystals) rather than amorphous material may indicate pathological conditions requiring further investigation 3
- When amorphous material obscures analysis in a clinically significant situation, recollection or alternative processing methods should be considered 1