Urine sediment preparation for microscopic analysis

Preanalytical factors: A suboptimal urine collection can affect the accuracy of the urine test results by introducing contaminating bacteria and epithelial cells from skin or vaginal secretions into the sample.

Preservation of urine samples is essential for reliable assessments of urinary sediment. Urine samples should be refrigerated if testing cannot be performed within two hours of collection unless an acceptable preservative has been added to the sample container.

In the microscopic examination, red blood cells and white blood cells may be under-reported as a result of lysing that could occur, particularly if the aged sample has a low specific gravity and/or is alkaline. Bacteria may also proliferate in an unpreserved sample held at room temperature for a prolonged period of time.

There are many variables in the manual preparation and visualization of urine sediment that could impact the accuracy of the reported elements. Factors that are subject to variation include:

  • Mixing of sample
  • Sediment preparation method
  • Volume of sediment examined
  • Number of fields examined
  • Method and equipment for visualizing sediment
  • Result reporting

Procedure for wet mount preparation of the Urine sediment-

1) Mix the urine thoroughly and pour approximately 12 ml of the

specimen into a plastic conical centrifuge tube.

2) Spin the tube at 1800 RPM (400-450g) for 5 mins.

3) Remove specimens from the centrifuge and return to the test tube rack

4) Remove approximately 11 ml of supernatant and re-suspend the

centrifugate within the remaining 1 ml of urine supernatant.

5) Using auto pipette, transfer one drop of re-suspended centrifugate to

the Slide.

6) Cover it with cover slip.

7) Search the whole area of the cover slip with the low power objective.

Adjust the light so that it is subdued and the sediment can be more

clearly seen. Adjust the fine focus continuously up and down to see

the elements at various levels in the urine. This gives a general

impression of the sediment.

8) Switch to the high power objective to identify all the constituents.

9) Count the various formed elements of clinical significance seen in

about 10 fields and report the average number in each high power


10) Supravital stains can be used to aid identifying cellular elements in bright field microscopy like 0.5% Toluidine Blue can be used to differentiate between WBCs and renal tubular epithelial (RTE) cells.Sudan III/Oil Red O Identification of free fat droplets, oval fat bodies, and lipid-containing cells and casts.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.