Purpose
A concentration procedure is performed mainly to separate the parasites from fecal debris. The concentration procedure not only increases the numbers of parasites in the sediment but it also unmasks them, making them more visible by removing organic and inorganic debris. In most cases the diagnostic parasitology laboratory does not know the consistency of the fixed(SAF) stool, therefore a full concentration and permanent stain are recommended. (1)
The Formalin-ether sedimentation technique will be explained here.
Step One
Thoroughly mix the stool and examine looking for blood, mucous, pus and worms. The above case although extreme was submitted as stool for ova and parasite examination. If the stool was poured without gross examination these Taenia species proglottids may have been missed.
Step Two
Pour the stool onto a double layer of wetted gauze taking special care to include any blood or mucous in the specimen.
Step Three
Wash the stool through the gauze using saline. This washes the parasites through but filters out the larger pieces of debris.
Step Four
Pour 2 - 3 ml. of stool mixture into a conical tube. The amount is of course dependent on the
thickness of the stool.
Add approximately 10 ml. of saline to the tube.
Step Five
Centrifuge the mixture for 10 minutes at 500 g. Please refer to a centrifuge nomograph for the correct r.p.m. for your centrifuge.(11) Pour off the supernatant. The sediment may be washed again if desired.