Microscopic Examination of the Urine PDF

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Summary

MICROSCOPIC EXAMINATION OF THE URINE The least standardized and the most time consuming part of the routine urinalysis. FUNCTION To detect and to identify insoluble materials present in the urine. MACROSCOPIC SCREENING CORRELATIONS Screening Test Significance Color Clarity Blood Hematuria vs. a Bloo...

Description

MICROSCOPIC EXAMINATION OF THE URINE The least standardized and the most time consuming part of the routine urinalysis. FUNCTION - To detect and to identify insoluble materials present in the urine.

MACROSCOPIC SCREENING CORRELATIONS Screening Test Significance Color Clarity

Blood Hematuria vs. Hemoglobinuria/Myoglobinuri a

Blood Protein Nitrite

Confirm pathologic or nonpathologic cause of turbidity RBCs/RBC cast Cast/cells Bacteria/WBCs

Leukocyte esterase Glucose

WBCs/WBC cast/bacteria Yeast

Contributes to the formed elements of the urine  Blood  Kidney  Lower genitourinary tract  External contamination Urine sediments           

RBC WBC Epithelial cells Casts Bacteria Yeast Parasites Mucus Spermatozoa Crystals Artifacts

-no clinical significance and considered normal unless they are present in increased amounts. Chemical sieving - refers to macroscopic screening.

Specimen Preparation  Freshly voided urine or adequately preserved urine.  Diluted alkaline urine – formed elements (RBCs, WBCs and hyaline casts) disintegrate rapidly.  Refrigeration may cause precipitation of amorphous urates and phosphates and other non-pathologic crystals.  37°C - prior to centrifuging is the recommended temperature in warming the specimen.  Midstream clean-catch specimen minimizes external contamination of the sediment  Dilute random specimen may cause false-negative readings Specimen Volume    

10-15 mL – standard amount of the urine. In centrifuging – 2000 rpm per 5 mins. 12 mL – frequently used. If obtaining 12 mL is not possible - the volume of the specimen used should be noted on the report form

Sediment Volume

Sediment Stains Stains

 0.5 to 1.0 mL Examination of the Specimen  LPO - to detect casts and to ascertain the general composition of the sediment.  HPO - for identification.  Conventional glass-slide method - casts have a tendency to locate near the edges of the cover slip. SOLUTION: use LPO.  Bright-field microscopy - when sediments are unstained.  Artifacts are larger than the sediment.

SternheimerMalbin

Toluidine blue

2% acetic acid

Reporting of Microscopic Examination SEDIMENT Cast RBC WBC Epithelial cells, crystals, and other elements

REPORTING Ave. # per LPF Ave. # per 10 HPF Ave. # per 10 HPF Semiquantitive terms (rare, few, moderate, many or 1+, 2+, 3+ and 4+)

Lipid stains: Oil Red O and Sudan III

Gram stain

Hansel stain

Prussian Blue

Description The most frequently used stain in urinalysis. Consist of crystal violet and safranin O. Provides enhancement nuclear detail. Lyses RBCs and enhances nuclei of WBCs. Used to confirm the presence of triglycerides (in orange stain) and cholesterol (does not stain). Microscopy used: POLARIZING MICROSCOPY Used primarily in microbiology in differentiating grampositive bacteria from gram-negative bacteria. Consist of methylene blue and eosin Y Stains structures containing iron

Function Identified WBCs, epithelial cells and casts.

Differentiates WBCs from renal tubular epithelial (RTE) cells. Differentiates RBCs from WBCs, yeast, oil, droplets and crystals. Identifies free fat droplets and lipidcontaining cells and casts.

Identifies bacterial casts

Preferred stain in identifying urinary eosinophils. Identifies yellowbrown granules of hemosiderin in cells and casts.

Urinary Microscopy  Resolution – the ability of the lens to distinguish two small objects that are specific distance apart.  The shorter the wavelength, the greater the resolving power of the microscope.  Objectives of the microscope: 1. Ocular field/objective – 10x 2.Low power field/objective – 10x* 3. High power field/objective – 40x* 4. Oil Immersion – 100x * - for urinalysis Total magnifications LPO – 100x (combination of ocular and other objectives) HPO – 400x OIO – 1000x

TYPES OF MICROSCOPY

Polarizing Microscopy  Used in urinalysis to confirm the identification of fat droplets, oval fat bodies, and fatty casts that produce a characteristic Maltese cross pattern.  Has a birefringent property which indicates that the element can refract light in two dimensions at 90° to each other.  Relies on: polarizing filter Interference-contrast Microscopy  Provides a 3D image showing very fine structural detail by splitting the light ray so that the beams pass through different areas of the specimen.  Types: 1. Hoffman or modulation contrast - a split aperture is placed below the condenser, a polarizer is placed below the split aperture, and an amplitude filter is placed in back of each objective. 2. Nomarski or differential interference-contrast microscope - uses prisms. Dark-field Microscopy

Bright-field microscopy  Objects appear dark against a light background.  It is the most frequently used in the clinical laboratory.  Employs the basic microscope previously described with a light source emitting light in the visible wavelength range.  Relies on: ordinary light. Phase-contrast Microscopy  Adaptation of a bright-field microscope with a phasecontrast objective lens and a matching condenser.  Relies on: refractive index

 To enhance visualization of specimens that cannot be seen easily viewed with a bright-field microscope.  Used to identify unstained specimens, particularly, Treponema pallidum. Fluorescence Microscopy  Used to detect bacteria and viruses within cells and tissues through a technique called immunofluorescence.  For serological testing  Relies on: acridine orange stain and UV light

SEDIMENT CONSTITUENTS...