Urinalysis and Microscopic Examination of Urine Sediment

The process of urine sediment examination involves using fine adjustment for continuous focusing to achieve a complete representation of sediment constituents.
Viewing guidance is available via online resources (e.g., Video 7-2 at www.fadavis.com).

Tip 7-3: Utilize reduced light levels when performing bright-field and phase-contrast microscopy, applicable at both low power (10x) and high power (40x) magnifications during sediment examination.

Terminology Variability: Terminology and reporting methods may vary slightly between laboratories; however, consistency within a particular system is crucial.
Casts Reporting: Report casts as the average number per low-power field (lpf), typically after examining 10 fields.
RBCs and WBCs Reporting: Report red blood cells (RBCs) and white blood cells (WBCs) as the average number per 10 high-power fields (hpf).
Reporting Other Elements: Epithelial cells, crystals, and additional elements are often reported semiquantitatively using terms such as rare, few, moderate, many, or in a scale of 1+ to 4+.
Reference Values: Laboratories must establish specific reference values in relation to the sediment concentration factor utilized.
- For example, Urisystem utilizes a concentration factor of 30, yielding a reference value for WBCs of 0 to 8 per hpf, contrasting with the conventional value of 0 to 5 per hpf using a factor of 12.

The conversion of average counts of elements per lpf or hpf into numbers per milliliter of urine provides a standardization across varying techniques. Steps include:
1. Area Calculation of hpf or lpf:
- Use manufacturer-supplied diameter to find area using formula:
  $ext{Area} = ext{π}r^2$ .
- For diameter of hpf = 0.35 mm:
  $ext{Area} = 3.14 imes (0.175)^2 = 0.096 ext{ mm}^2$ .
1. Maximum Number in Viewing Area:
- For area under a 22 mm x 22 mm cover slip:
  $rac{484 ext{ mm}^2}{0.096 ext{ mm}^2} = 5040 ext{ hpfs}$ .
1. Calculation of hpfs per mL:
- For urine tested based on concentration factor and sediment volume examined:
  $rac{5040}{0.02 ext{ mL} imes 12} = 21,000 ext{ hpfs/mL of urine}$ .
1. Count of Formed Elements:
- Calculate the number of formed elements per mL:
  $4 ext{ WBC/hpf} imes 21,000 ext{ hpfs/mL of urine} = 84,000 ext{ WBC/mL of urine}$ .
This methodology ensures that the number of lpfs and hpfs per mL of urine remains consistent across examinations when the same microscope and volume are employed, streamlining calculations.

Laboratories should weigh the pros and cons of introducing an additional computation in microscopic studies.
The Clinical and Laboratory Standards Institute (CLSI) emphasizes that reporting decisions regarding microscopic examination should align with individual laboratory needs, requiring comprehensive documentation of procedures to be adhered to by all personnel.

It is imperative to correlate microscopic results with physical and chemical findings for reporting accuracy.
In instances of discrepancies between results, it is necessary to verify both technical and clerical errors.
Table 7-2 details common correlations in urinalysis while accounting for element numbers or chemical presence and potential interferences with chemical tests, alongside specimen age.

Tip 7-4: Recheck urine specimens for potential technical and clerical errors, particularly if there's a lack of correlation between physical, chemical, and microscopic results.

Numerous factors can affect the appearance of urinary sediment, which may include:
- Cells and casts at various developmental stages.
- Distortion of elements by the specimen's chemical content.
- Presence of inclusions within cells or casts.
- Possible contamination from artifacts.
Accurate identification of constituents can be challenging, even for seasoned technicians, due to these factors.

The Addis Count introduced by Addis in 1926 aimed to standardize the quantification of formed elements in urine through microscopic analysis.
- It employed a hemocytometer to quantify RBCs, WBCs, casts, and epithelial cells within a 12-hour urine specimen.
- Normal value ranges approximate:
- 0 to 500,000 RBCs
- 0 to 1,800,000 WBCs and epithelial cells
- 0 to 5000 hyaline casts
While the Addis Count was primarily utilized for monitoring diagnosed renal disease cases, it has since been superseded by various standardized commercial systems for the preparation, examination, and quantification of formed elements in non-timed urine specimens.