In immunochromatographic rapid diagnostic tests (RDTs) for malaria, the 'control line' appearing regardless of test outcome serves to:

• A Confirm the presence of Plasmodium falciparum antigen (HRP2) in the sample
• B Detect Plasmodium vivax-specific pLDH antigen separately from falciparum
• C Verify that the test device is functioning correctly and adequate sample/conjugate has flowed ✓
• D Indicate a high parasitaemia requiring quantitative confirmation by microscopy

Explanation

In lateral flow immunochromatographic RDTs, the control line contains antibody against the gold-conjugate (usually anti-species antibody against the conjugate antibody), and it always appears when the test has run correctly — it is a procedural control, not a disease result. If the control line is absent, the test is invalid regardless of the test line result. The test line(s) detect specific malaria antigens (HRP2 for P. falciparum, pan-pLDH or aldolase for all Plasmodium species). Control line appearance confirms adequate capillary flow and reagent function; a missing control line indicates device failure.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.