Physician Performed Microscopy Procedure

Principle

Microscopic urine examination serves as an adjunct to medical history taking and physical examination in an outpatient setting. Physicians performing these tests should keep in mind their technical limitations as well as the attending practitioner's complete responsibility for microscopic examinations performed by residents or other staff. Physician performed microscopy, like all laboratory procedures, is subject to the rules of good laboratory practice. Among these rules of good practice is confirmation of significant diagnoses by multiple test methods, when such are available and clinically appropriate.

The providers performing the test must have had specific training in this mode of testing from their professional training. They will also be oriented to the specific procedures in place at the hospital. The competency assessment is monitored by the credentialing committee.

These tests must be performed by a physician on the physician's own patients and must be carried out in compliance with good laboratory practices regarding:

1. proper specimen collection, especially patient identification,
2. maintenance of the testing site, and
3. proper record keeping, especially result recording.

Specimen Collection

The urine should be collected in a labeled clean, plastic container with adequate (e.g. 50 mL) capacity and a screw tip lid. During and after examination, excess specimen should be disposed of. The urine specimen should be tested within 30 minutes of collection. Urine should not be tested if left at room temperature for more than two hours. Artifacts introduced by longer delay include:

• dissolution of casts
• variation in presence of appearance of some crystals
• lysis of cells (both human and bacterial)
• miscellaneous changes, such as bacterial overgrowth

The usual acceptable volume for routine examination is at least 12 mL of urine. Distribution or presence/absence of casts, crystals, cells (human or bacterial), or other miscellaneous elements is likely to be unrepresentative in smaller samples, especially among children out of the newborn period. Such small specimens should be examined directly without centrifugation ("unspun urine").

Testing Site

The urine microscopic examination should be performed on a designated area of the counter top. This area should be wiped down with a paper towel before and after each use. On the counter top should be a centrifuge with centrifuge tubes, disposable pipettes, microscopic slides, coverslips, the examining microscopes, and a notebook with the log sheets where the results are recorded. The equipment should be kept clean by wiping down after each day of use.

Procedure

1. Gross examination of the urine specimen for color, clarity, odor, amount, and color of foam and the chemical examination (urine dipstick for pH, specific gravity, protein, hemoglobin, nitrite, leukocyte esterase, glucose, ketone, and bilirubin) should be performed by a certified operator and the results recorded according to the Urine Dipstick Procedure.
2. The 12 mL of urine aliquot of well-mixed urine is centrifuged at 400g for 5 minutes.
   1. Note: aliquots of urine less than 12 mL should be examined without centrifugation.
   2. Note: aliquots less than 3 mL will yield highly misleading results.
3. 11 mL of supernatant are pipetted off and discarded in the sink.
4. The remaining 1 mL of urine should be mixed well, ensuring the button on the bottom of the centrifuge tube is resuspended in the urine.
5. A drop of the urine left in the centrifuge tube is dropped onto a microscope slide and covered with a coverslip.
6. The urine under the coverslip is scanned with the 10X objective (across "low power fields") and the identity of constituents is confirmed using the 40X objective (in "high power fields"). The slide should be viewed with the light sufficiently reduced by closing the condenser aperture diaphragm to increase contrast. Increased contrast makes casts and cells easier to visualize.
7. Results are recorded on the log sheet provided by the Clinical Laboratory. Refer to the section "Result Reporting" for proper documentation procedures.

Result Reporting

The following categories of findings deserve classification, semi quantification, and reporting.

The results are to be recorded on the log sheet provided by the Clinical Laboratory, as well as in the patient chart.

The patient's name, medical record number or date of birth, date of examination, the results of the microscopic examination, and the name of the examining physician are to be recorded on the log sheet provided by the Clinical Laboratory.

Questions regarding this procedure are to be referred to the POCT Coordinator at (302) 651-4324 or the Microbiology Department at (302) 651-5658 or (302) 651-5659.