1. "Centrifugation is no more accurate than simple flotation." Research has confirmed that centrifugal flotation is more effective than simple flotation in recovering parasites from fecal
samples.2-4 The reason is simple: The buoyant and centrifugal forces that we can apply to the solution containing the parasites when
we spin the tubes in the centrifuge are much greater than the forces of buoyancy and gravity that we use to concentrate parasites
during simple flotation. Recovery rates were particularly improved for heavier eggs such as Trichuris vulpis (whipworms) and Taenia species (tapeworms) as well as for Toxocara species (roundworms), Eucoleus (Capillaria) species (roundworms), and Isospora (coccidia) species when centrifugal flotation was used.2-4 Given that well-cared-for pets are more likely to harbor a lower burden of parasites, it is important to use centrifugation
to increase parasite recovery rates.3
2. "Centrifugation is too complex and requires too much time." Centrifugation is easy and fast.
3. "A centrifuge is too large and occupies too much valuable counter space in busy veterinary practices." Swinging bucket and fixed-angle centrifuges require little hospital bench space. Many are less than 16 in long.
4. "The cost of a centrifuge is prohibitory for many practitioners." Most centrifuges are reasonably priced and can be used for decades with minimal service and often little or no repair (see Tables 1 & 2).
5. "Centrifuge rotors allow a limited number of samples per centrifuge run." A variety of rotors are available to suit the needs of the busiest of practices.
COLLECTING AND STORING SAMPLES
The accuracy of any fecal examination procedure depends on the amount and quality of the fecal sample. We recommend using
at least 2 g of feces for fecal flotation; 2 g of firm, normal feces will form a cube about 0.5 to 0.75 in on a side. Occasionally
it is necessary to use a sample obtained with a fecal loop or a rectal thermometer. In these cases, a negative result is meaningless,
but a positive result can imply a high level of parasitism. Increase the sample size as the amount of water in the sample
increases. Contrary to what you might think, diarrheic fecal samples from animals with a large burden of parasites may contain
relatively few fecal parasite stages because of the dilution effect of the increased water content.
Table 1 Examples of Commercially Available Centrifuges with Swinging Bucket Rotors*