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Ova and Parasite (O&P) Examinations

Introduction | Macroscopic | Microscopic |

Microscopic Examination - Ova and Parasite Examination

Introduction | Direct Wet Smear | Concentration | Permanent Stained Smear

Concentration

Introduction | Formulas | Quality Control | Procedures | Results and Reporting | Procedure Notes | Procedure Limitations | Procedure Review | Tips and Pitfalls

Procedure Review

Topic Comments
Principle To concentrate the parasites present, either through sedimentation or flotation. The concentration is specifically designed to allow recovery of protozoan cysts, coccidian oocysts, microsporidian spores and helminth eggs and larvae.
Specimen Any stool specimen that is fresh or preserved in formalin, PVA (mercury- or non-mercury-based), SAF, MIF or newer single vial system fixatives.
Reagents 5% or 10% formalin, ethyl acetate, zinc sulfate (flotation procedure only [specific gravity of 1.18 for fresh stool; 1:20 for preserved stool]); 0.85% NaCl; Lugol's or D'Antoni's iodine.
Examination Low power examination (100X) of entire 22 x 22 coverslip preparation (iodine recommended, but optional); high dry power examination (400X) of at least 1/3 to 1/2 of the coverslip area (both saline and iodine).
Results and Laboratory Reports Often results from the concentration examination should be considered presumptive; however, some organisms could be definitely identified (Giardia lamblia cysts and Entamoeba coli cysts, helminth eggs and larvae, Isospora belli oocysts). These reports should be categorized as "preliminary" while the final report would be available after the results of the concentration and permanent stained smear were available.
Procedure Notes and Limitations

Formalin-ethyl acetate sedimentation concentration is the most commonly used. Zinc sulfate flotation will not detect operculated or heavy eggs; both the surface film and sediment will need to be examined before reporting a negative result. Smears prepared from concentrated stool are normally examined at low (100X) and high dry power (400X); oil immersion examination (1000X) is not recommended (organism morphology not that clear). The addition of too much iodine may obscure helminth eggs (will mimic debris).