Ova and Parasite (O&P) Examinations

Introduction | Macroscopic | Microscopic |

Microscopic Examination - Ova and Parasite Examination

Introduction | Direct Wet Smear | Concentration | Permanent Stained Smear

Permanent Stained Smear

Introduction | Trichrome Stain | Iron Hematoxylin Stain | Modified Iron Hematoxylin Stain | Procedure Review

Trichrome Stain

Quality Control

Stool samples used for quality control can be fixed stool specimens known to contain protozoa or PVA-preserved negative stools to which buffy coat cells (PMNs or macrophages) have been added. A quality control smear prepared from a positive PVA sample or a PVA sample containing buffy coat cells should be used when new stain is prepared or at least once each week. Cultured protozoa can also be used. REMEMBER TO REFER TO CAP CHECKLIST FOR ANY RECOMMENDED CHANGES PER QC FREQUENCY.
A QC slide should be included with each run of stained slides, particularly if the staining setup is used infrequently.
If the xylene becomes cloudy or there is an accumulation of water in the bottom of the staining dish, discard the old reagents, clean the dishes, dry thoroughly, and replace with fresh 100% ethanol and xylene.
All staining dishes should be covered to prevent evaporation of reagents (screw-cap Coplin jars or glass lids).
Depending on the volume of slides stained, staining solutions will have to be changed on an as-needed basis.
When the smear is thoroughly fixed and the stain is performed correctly, the cytoplasm of protozoan trophozoites will have a blue-green color, sometimes with a tinge of purple. Cysts tend to be slightly more purple. Nuclei and inclusions (chromatoid bodies, RBCs, bacteria, and Charcot-Leyden crystals) have a red color, sometimes tinged with purple. The background material usually stains green, providing a nice color contrast with the protozoa. This contrast is more distinct than that obtained with the hematoxylin stain, which tends to stain everything with shades of gray-blue.
The microscope should be calibrated, and the objectives and oculars used for the calibration procedure should be used for all measurements on the microscope. The calibration factors for all objectives should be posted on the microscope for easy access (multiplication factors can be pasted on the body of the microscope). Although some do not feel the microscope requires calibration every 12 months, if the microscope is periodically moved, receives hard use, or is serviced, it may require recalibration.
Known positive microscope slides, Kodachrome 2 x 2 projection slides, and photographs (reference books) should be available at the workstation.
Record all QC results; the laboratory should also have an action plan for "out of control" results.