Protozoa

Protozoa are unicellular eukaryotic parasites diagnosed in the clinical laboratory primarily by microscopy of cysts, trophozoites, or blood/tissue stages, with adjunct antigen or molecular methods as offered locally.

Record size (ocular micrometer), number of nuclei, peripheral chromatin, karyosome, chromatoid bodies, flagella, and cytoplasmic inclusions. Wet mounts show motility and outline; permanent stains show nuclear detail needed for many amoeba reports.

• Formed stool favors cysts; diarrheal stool favors trophozoites
• Preservative choice affects morphology and antigen testing options
• Concentration helps sparse cysts
• Blood protozoa require films, stool O&P is the wrong pathway

No numeric reference interval applies. Interpret detected/not detected with method and specimen-quality comments. Rules for number of stools examined and critical notification are institutional, verify local policy.

Pathogenic protozoa support infection diagnosis when criteria are met. Nonpathogenic amoebae/flagellates are reported as such when identified; they are not treatment targets in MLS comments.

Distinguish protozoa from yeast, leukocytes, epithelial cells, pollen, and stain debris. Separate E. histolytica complex morphologic calls from nonpathogenic Entamoeba using measured criteria and local adjunct assays when required.

Not applicable, laboratory morphologic frame, not a WHO disease list.

• Use a calibrated micrometer for cyst size
• Hedge permanent-stain menus and antigen differentiation as local
• No antiparasitic recommendations in report comments