Detection of microfilariae in peripheral blood
Test Id | Reporting Name | Available Separately | Always Performed |
---|---|---|---|
FILB | Filaria Bill Only | No, (Bill Only) | No |
In the event that microfilaria is discovered in the Knott Concentration; a Giemsa stain will be performed for identification at an additional charge.
See Mosquito-borne Disease Laboratory Testing in Special Instructions.
Concentrated, Microscopic Examination
Elephantiasis
Wuchereria bancrotfi
In the event that microfilaria is discovered in the Knott Concentration; a Giemsa stain will be performed for identification at an additional charge.
See Mosquito-borne Disease Laboratory Testing in Special Instructions.
Whole Blood Na Cit
Question ID | Description | Answers |
---|---|---|
Q00M0022 | Specimen Source |
Container/Tube: Light-blue top (sodium citrate)
Specimen Volume: 2.7 mL
Collection Instructions: Certain microfilariae have a nocturnal periodicity therefore the blood specimen is best drawn at night between 10 p.m. and 2 a.m.
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.
2 mL
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Whole Blood Na Cit | Ambient (preferred) | 72 hours | |
Refrigerated | 72 hours |
Detection of microfilariae in peripheral blood
In the event that microfilaria is discovered in the Knott Concentration; a Giemsa stain will be performed for identification at an additional charge.
See Mosquito-borne Disease Laboratory Testing in Special Instructions.
The filariae are parasitic nematodes (roundworms) that cause significant human morbidity in tropical regions worldwide. The macroscopic adults live in the human host and release microscopic offspring (microfilariae) into the blood or skin. The microfilariae of Wuchereria bancrofti, Brugia malayi, B timori, Loa loa, Mansonella perstans, and M ozzardi are found in the blood, while the microfilariae of Onchocerca volvulus and M streptocerca are found in the skin. If microfilariae are taken up by a biting insect vector (mosquitos, blackflies, midges, and deer flies), they undergo further development in the insect and can then be transmitted to other humans.
W bancrofti and the Brugia species cause a serious condition called lymphatic filariasis. The adults live in the lymphatics and cause inflammation and scarring of the lymph vessels. Over time, the lymphatic channels are obstructed and fluid cannot drain back to the heart, resulting in massive lymphedema (elephantiasis) of the affected limb or groin. W bancrofti is found in the tropics worldwide, while Brugia species are found in parts of Asia and Southeast Asia.
Loa loa causes migratory subcutaneous angioedema referred to as "calabar swellings" as the adult worm migrates throughout the body. The adult occasionally migrates across the surface of the eye, giving it the moniker "the African eye worm." Loa loa is only found in Africa.
Finally, M perstans and M ozzardi cause a relatively mild form of filariasis. Patients are often asymptomatic. When present, symptoms include fever, angioedema, headache, myalgias, arthralgias, pruritus, and neurologic manifestations. M perstans is found in parts of Africa and South America, while M ozzardi is only found in Mexico and Central and South America.
The microfilariae of these filarial worms can be seen on conventional thick and thin blood films, which allows for their definitive identification. However, microfilariae may be in low numbers and, therefore, use of concentration methods such as the Knott's technique improves the detection sensitivity. Some microfilariae are released into the blood at certain times of the day; W bancrofti and Brugia species are usually released between 10 p.m. and 2 a.m. (nocturnal periodicity), while L loa is released mostly from 10 a.m. and 2 p.m. (diurnal periodicity). It is therefore important to collect blood during these time periods for optimal detection sensitivity. Mansonella species microfilariae do not exhibit any periodicity and, therefore, a random blood draw is acceptable. Since the levels of parasitemia may fluctuate, multiple smears may be needed to detect the filarial worms. Blood should be obtained and examined every 8 to 12 hours for 2 to 3 days before excluding infection.
Negative
If positive, organism is identified.
Positive results are provided with the genus and species of the
This exam will not detect the microfilariae of Onchocerca volvulus and Mansonella streptocerca since they are found primarily in the skin. The "skin-snip" examination is the preferred method for detecting the microfilariae of these worms.
Microfilariae may be seen in peripheral blood on routine thick and thin blood films, but concentration techniques such as the Knott's concentration and Nucleopore membrane filtration technique offer increased detection sensitivity.
Multiple smears may be needed to detect microfilariae in blood. Repeat specimens can be collected every 8 to 12 hours over a period of 2 to 3 days.
The blood collection should be timed to correspond with the release of microfilariae in the peripheral circulation. For the agents of lymphatic filariasis, blood should be collected between 10 p.m. and 2 a.m., whereas for detection of Loa loa, blood should be collected between 10 a.m. and 2 p.m.
Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria. DPDx, Diagnostic Procedures. 2013. Available at http://www.cdc.gov/dpdx/diagnosticProcedures/blood/specimencoll.html
A portion of the blood specimen is concentrated by centrifugation after adding 2% formalin. The sediment is examined as a wet preparation and, if positive, the slide is air dried, fixed in methyl alcohol, and stained with Giemsa to aid in species identification.(Garcia L: Diagnostic Medical Parasitology. Fifth edition. Washington, DC, American Society for Microbiology, 2005)
Monday through Friday
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.
87015
87210
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
FIL | Filaria, B | 10662-5 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
FIL | Filaria, B | 10662-5 |