Proper specimen collection should be informed by the lab. Physicians, health care workers, and patients must comply in order to obtain the best outcomes. Depending on the level of infection, searching a wet prep for a parasite can be time-consuming and lead to false negatives.
Here are some recommendations that will help yield the best results:
- More than one stool specimen should be submitted to increase the chances of finding something. It is often recommended to submit a stool specimen from three consecutive days, or possibly at intervals of 2-3 days.
- The stool specimen should be as fresh as possible or in a preservative. 10% formalin is recommended if a worm infection is suspected, and the specimen will be concentrated for microscopic exam. Other recommended fixatives for concentration include: Merthiolate-Iodine-Formaldehyde (MIF) and Sodium acetate-acetic acid-formalin (SAF). Note that although Polyvinyl Alcohol (PVA) is an excellent preservative when making permanent stained smears (which are not that useful for worm eggs), it is not appropriate for concentration procedures. Also, Schaudinn's fixative is not recommended for worm eggs as it does not preserve them very well and it is not to be used with concentration techniques.
- If PCR based testing is to be performed, the stool should be put in a preservative that is compatible with PCR based tests, such as "TotalFix", "Unifix", modified PVA(Zn or Cu based), or "EcoFix". If such preservatives are not available, storing the stool specimen in the cold or freezing is an alternative. PCR tests are more widely available for protozoan parasites than for worms. The advantage of these fixatives is that both permanent stained smears and concentration techniques can also be performed on specimens preserved in these.
