Microscopic Examination of Urine

Substances that rotate plane-polarized light in a clockwise manner display positive birefringence.
Substances that rotate it counterclockwise show negative birefringence.

Obtained using two polarizing filters arranged in a crossed configuration:
- First Filter (Polarizing Filter): Located in the condenser filter holder and allows light vibrating in one direction.
- Second Filter (Analyzer): Positioned between the objectives and the ocular, blocks all incoming light vibrations not aligned with the first filter.
Birefringent crystals produce characteristic visual patterns when positioned between cross-polarizing filters.
Bright-field microscopes can be adapted for this technique, requiring installation of two polarizing filters:
- First filter (Polarizer): Placed in the condenser.
- Second filter (Analyzer): Placed above the objectives.
Bright-field adaptation allows visualization of birefringent objects, which typically appear white or colored against a black background.

Red Compensated Polarizing Filter: Can be added to enhance visualization by dividing light into slow and fast vibrations, improving the ease of identifying crystals that align with the slow vibration, showing colors like blue or yellow.
Utilization in urinalysis allows for the confirmation of:
- Fat droplets
- Oval fat bodies
- Fatty casts exhibiting characteristic Maltese cross patterns
Birefringent crystals in urine include:
- Uric acid crystals differentiated from cystine crystals.
- Monohydrate calcium oxalate crystals versus nonpolarizing RBCs.
- Calcium phosphate crystals versus nonpolarizing bacteria.

Provides a 3D image illustrating structural details through light splitting.
Allows visualization of fine details, with an object appearing bright against a dark background.
More complex than bright-field microscopy, requiring extensive modifications, hence not routinely used in urine analysis.

Modulation-Contrast Microscopy (Hoffman)
- Three modifications include:
1. Split aperture with a polarizing filter below the condenser.
2. A polarizer for contrast control beneath the split aperture.
3. Amplitude filter (modulator) behind each objective with varied light transmission zones (10%, 15%, 100%).
- Converts polarized rays into variations of light intensity, creating a 3D image.
Differential Interference-Contrast Microscopy (Nomarski)
- Employs birefringent crystal prisms as beam splitters to distinguish intensity variations in specimens.
- Requires a polarizing filter for plane-polarized light, condenser with Wollaston prisms, and additional polarizing filters.
- Utilizes a two-layered Nomarski-modified Wollaston prism for separating and recombining light rays, leading to interference and resulting in 3D imagery.

Enhances visualization of specimens not easily seen under bright-field microscopy, particularly unstained objects such as Treponema pallidum.
Conducted by swapping the regular condenser for a dark-field condenser containing an opaque disk.
Light enters the specimen obliquely, resulting in a dark field with light specimens highlighted through scattering.

Expanding use in medical diagnostics to identify bacteria and viruses in cells/tissues using immunofluorescence.
Fluorescence: Ability of atoms to absorb and emit light at particular wavelengths.
- Practical application involves visualizing naturally fluorescent substances or those stained by fluorochromes.
- Specimen illumination through specific wavelength light followed by the detection of emitted light via filters.
- Special filters:
- Excitation Filter: Selects excitation wavelength.
- Emission Filter: Allows visualization of emitted light.
- A dichroic mirror reflects excitation light while transmitting emitted light through to the emission filter and onto a detector.
Requires powerful light sources (often mercury or xenon arc lamps).

Normal urine sediment may vary and might include formed elements like RBCs, WBCs, and hyaline casts.
Minor elements like abnormal cells or structures could create confusion as they often get emphasized in educational contexts.

Misidentification can happen due to variations in concentration, pH, and metabolites present in urine, complicating identification efforts.
- Average Count Values:
- RBCs: 0-3 per hpf
- WBCs: 0-5-8 per hpf
- Hyaline casts: 0-2 per lpf
Contextual factors affecting urine analysis include:
- Recent stress/exercise
- Menstrual contamination
- Presence of sediment constituents.

Appear as smooth, nonnucleated, biconcave disks measuring 7 mm in diameter, identifiable under high power microscopy (400x).
- Counted as average numerics in 10 hpf.
In Urine:
- In concentrated urine: May appear crenated due to water loss.
- In dilute urine: Cells absorb water leading to swelling or lysis, forming ghost cells (difficult to see under low light).
Identifying difficulty arises from their structural lack, size variations, and resemblance to other constituents (e.g., yeast cells).
- RBCs are frequently misidentified as yeast or oil droplets:
- Yeast shows budding.
- Oil droplets and air bubbles are highly refractile.
Dysmorphic RBCs:
- Indicate potential renal bleeding, often associated with renal injury or dysfunction.
Clinical significance of RBC presence includes:
- Damage to glomerular membranes or vascular injury.
- Presence ratio indicative of injury severity.

Larger than RBCs (12 mm diameter); can be identified more easily by granules and multilobed nuclei (neutrophils are prevalent).
- Identification: Counted average numerics in 10 hpf.
- Lysis can occur rapidly in dilute alkaline urine.

Appear as large cells stained with Sternheimer-Malbin stain showing distinguishable properties.
Glitter Cells: Swollen neutrophils in hypotonic urine showing brownian movement.

Present mainly during drug-induced interstitial nephritis or with urinary tract infections (UTIs).
Often require concentration and specific stains for detection (Hansel stain is most preferred).

Include lymphocytes, monocytes, macrophages, and histiocytes typically not identified in routine wet preparations.
Can resemble RBCs and be indicative of transplant rejection stages.

Epithelial Cells:
- Larger than RBCs, originate from genitourinary linings, potentially normal when sporadically present but abnormalities may suggest pathology.
- Squamous, transitional, and renal tubular epithelial cells are categorized based on their source.
Squamous Epithelial Cells:
- The largest, often indicate normal sloughing unless abnormally abundant (from contamination).
- Particularly noted in females, with