Urine sediment

 

urine sediment examination

This is the final stage of a complete urinalysis. It can confirm suspected findings from earlier stages of the analysis as well as facilitate visual inspection of structures in the sample e.g. casts, cells or crystals.

Before examining the sediment the urine must be centrifuged or "spun down" to concentrate the sample. This process will separate the sample into two parts: the supernatant and the sediment.

Equipment:

  • Centrifuge tubes (conical tip, 2ml capacity is typical)
  • Centrifuge
  • Microscope
  • Glass slides
  • Cover slips 
  • Disposable gloves
  • Sediment stain (if preferred)
  • Disposable pipette
  • Sharps bin
  • Refuse bin
  • Clinical waste bin

Sediment stain can be useful as many of the sediment elements are translucent. The stain provides contrast and so aids visualisation. However it can also obscure some details. Personally I prefer to examine the unstained slide microscipcally first and then add a single drop of stain to the slide and examine it again. Over time the stain may percipitate into clumps or become contaminated with bacteria: if these are found the stain should be replaced.

Procedure

See the video below.

Check your hands are clean (wash if necessary) before donning disposable gloves. Mix the urine sample thoroughly before filling two conical centrifuge containers. Balance the centrifuge by inserting both samples opposite each other. Centrifuge for 3-6 minutes at 1000-2000 rpm (five minutes at 1500 rpm is typical).

Decant the supernatant off the sediment, discarding it in a sink. Leave approximately 0.5-1ml of supernatant in the tube. Close the lid and resuspend the sample by gently flicking the tube with your finger or mixing the content with a pipette.

Pipette a drop of the resuspended sediment onto a glass slide and gently (to minimise air bubbles) place a coverslip over it. Place the slide on the microscope stage. Increase the light contrast by partially closing the microscope iris diaphragm. Stage the stage height by adjusting the coarse focus at 4x. Change to 10x and scan the entire slide for the presence of large cells, crystals or casts. Switch to high power (40x) and methodically scan the entire sample using the battlement technique to identify the structures present.        

If you wish to use stain either add a drop to the sample by placing it on the edge of the coverslip, or place a second drop of the sample on the end of the slide and add a drop of stain before applying a coverslip and examine as above.

Casts are reported as average number per low power field (10x).

Cells are reported by type (RBCs, WBCs, sperm) and average number per high powered field (40x).   

Bacteria and crystals are examined at 40x and reported as occasional (1+), few (2+), moderate (3+) or many (4+).

See Sediment analysis guide  to interpretation (from IDEXX Laboratories).

See this page for an overview of urinalysis findings from the Merck Veterinary Manual.  

 

How to examine urine sediment

Further reading

Sirois, M. (2015). Laboratory Procedures for Veterinary Technicians, 6th ed. Elsevier: St. Louis.