Faecal Parasite diagnosis - UKAS accredited test
Faecal microscopy (including hot stool)
A concentration technique is routinely performed on all faecal samples for the presence of cysts, ova and larvae. Direct saline smears are examined on samples that are 24 hours old or less where trophozoite stages of protozoan parasites are suspected.
Sample requirement: Minimum of ¼ specimen pot of faecal sample. Ova, cysts and parasites may be passed intermittently therefore three samples may be required to be examined. Ova, cysts and parasites will diminish over time therefore it is more ideal for the sample to be less than 2 days old upon receipt at LSTM, however older stools will not be rejected.
Key factors affecting test: trophozoites may only survive for up to 24 hours in voided faecal samples
If Entamoeba histolytica trophozoites are suspected a “hot” stool must be examined.
Hot stool sample requirement: specimen must reach the laboratory within 30 minutes of sample being produced and must be marked as hot stool, this will then be examined with priority. Methanol fixed faecal smears can be made at requesting site if the sample can not arrive at CDPL within 30 minutes, these smears can then be sent to CDPL for staining and examination.
Culture for Strongyloides / Hookworm
Faeces are cultured for filariform larvae using the charcoal technique.
Sample requirements: At least 50g (half pot) of faeces is required for this test. Ova, cysts, and parasites may be passed intermittently therefore three samples may be required to be examined.
Key factors affecting tests: samples should NOT be stored in a refrigerator/cold room following collection as this may inhibit subsequent larval growth.
Whole worms / proglottids
Identification of whole worms/proglottids
Sample requirements: Whole worms such as Ascaris may be stored in 10% formol saline. Suspected Taenia species proglottids are best stored in physiological saline and sent to the laboratory as soon as possible. The use of 10% formol saline should be avoided unless the sample cannot be sent to the reference laboratory within 3 days.
Key factors affecting tests: Identification may be difficult if formalin-fixed proglottids are sent for identification, however proglottids may disintegrate if in saline for 3 days or more.
Enterobius vermicularis microscopy
The rectal swab method is used in preference to sellotape slides, however both means of sample collection will be examined.
Sample requirements: a cotton bud dampened with physiological saline is wiped around the peri-anal area, and placed in a small bottle of physiological saline. The bottle is sent to the laboratory for examination. OR adhesive tape is applied to the area, attached sticky slide down to a microscope slide and sent to the laboratory for examination.
Key factors affecting test: ideally the swab / sellotape sample should be taken in the morning before washing the peri-anal area.
Sputum microscopy is performed for parasitic ova.
Specimen requirement: Age and volume of sample is not critical. The laboratory does not process samples when a diagnosis of TB cannot be excluded.