4. Yeast, Parasites and Bacteria

4.1 Yeast

Morphology:  Yeast appear as small round or oval shaped structures, similar in size to RBCs.  They are typically more refractile than RBCs.  Yeast can be seen in multiple forms including single celled, budding cells (footprint appearance), pseudo-hyphae and branching hyphae.

Disease correlation and clinical significance: Yeast can cause urinary tract infections.  Individuals who are immunocompromised or diabetic are more susceptible to yeast related UTIs than the general population.  In urine samples from women, the presence of yeast may occur due to contamination from a vaginal yeast infection.

Helpful Hints: Single celled yeast and RBCs look similar in structure.  To distinguish between RBCs and yeast, acetic acid (1:1) can be added to urine sediment.  RBC will lyse in the presence of acetic acid but yeast will remain intact.

4.2 Pinworm (Enterobius vermicularis)

Morphology: Pinworm eggs are oval shaped with one side slightly flatter than the other. They have a large nucleus and a thick cellular wall.  The size of the egg varies but is similar to the size of a squamous cell or larger.

Disease correlation and clinical significance:  Pinworm eggs in urine are typically from fecal contamination and suggest an intestinal pinworm infection.

4.3 Trichomonas

Morphology:  Trichomonas are similar in size and appearance to WBCs and RTE cells, however trichomonas are slightly pear shaped and have a tail-like flagella.

Disease correlation and clinical significance: Trichomoniasis is a sexually transmitted parasitic disease. Trichomonas in female urine arises due to contamination from vaginal secretions when the female has a Trichomonas vaginalis infection. 

Helpful Hints:  Trichomonads look similar to WBCs and RTE cells, to differentiate look for movement of the flagella. 

4.4 Bacteria

Morphology: Bacteria can appear as small round or rod-shaped structures.

Disease correlation and clinical significance:  Bacteria are associated with urinary tract infections but can also be normal flora of the outer genitalia.  Bacteria associated with a UTI will also show the presence of WBCs in urine and/or be leukocyte esterase positive on the chemical strip test.

Helpful Hints: It is difficult to distinguish bacteria from amorphous crystals. To differentiate, bacteria will exhibit motility whereas amorphous crystals will not.