Question
DEC provocation test
Answer
The DEC (Diethylcarbamazine) provocation test is used to enhance the detection of microfilariae (particularly Wuchereria bancrofti) in peripheral blood when routine nocturnal blood collection is impractical, or in suspected cases with occult/low-density microfilaraemia.
Principle: a single oral dose of DEC (a filaricidal drug) is given during the daytime, when circulating microfilarial density is normally at its lowest (due to nocturnal periodicity); DEC provokes a rapid mobilization of microfilariae from the pulmonary capillary bed into the peripheral circulation within about 15–30 minutes to an hour, allowing detection on a blood smear taken shortly afterward, without needing to wait for or collect blood at midnight.
Procedure: a test dose of DEC (typically 50–100 mg in adults) is administered orally; peripheral blood samples are then taken at set intervals (e.g., 15, 30, 45, and 60 minutes) after administration and examined microscopically for microfilariae.
Clinical/practical significance: provides a practical alternative to the inconvenient requirement for midnight blood collection dictated by nocturnal periodicity, particularly useful in outpatient/field settings where night-time sample collection is not feasible; a positive test (microfilariae detected) confirms active microfilaraemia, while a negative test does not entirely exclude infection given some variability in test sensitivity.
Limitation: less commonly used now with the availability of the circulating filarial antigen (CFA) test, which detects adult worm antigen and is entirely independent of periodicity or provocation, offering a simpler and increasingly preferred diagnostic alternative.