The Widal test is a blood test that can help diagnose typhoid fever, also known as enteric fever: How it worksA patient's serum is mixed with antigens from the bacteria that causes typhoid fever, and then tested for antibodies against those antigens. If antibodies are present, the test is positive. HistoryThe Widal test was developed in 1896 by Georges-Fernand Widal.UsageThe Widal test is still used in many developing countries, but is not commonly performed in the United States and other developed countries. LimitationsThe Widal test can produce false positives or false negatives for a number of reasons, including: Vaccination against typhoid fever Infections with other bacteria Performing the test too early in the disease course ProcedureThe Widal test involves drawing a blood sample from a vein in the arm, and then transferring the sample to a lab for processing

Dengue IgM and IgG antibodies can be used to determine if someone has been infected with the dengue virus, and to differentiate between primary and secondary infections: IgM antibodiesThese antibodies are produced early in an infection, and can be detected 3–7 days after exposure. A positive IgM test indicates a recent infection, but it can also be caused by a cross-reaction with a similar virus like chikungunya. IgM antibodies can remain detectable for up to 6 months after the infection has resolved. IgG antibodiesThese antibodies are produced 7–14 days after infection, and can be detected for months or even years. A positive IgG test indicates exposure to the virus in the past. IgM/IgG ratioThe ratio of IgM to IgG antibodies can be used to distinguish between primary and secondary infections. A primary infection is indicated by an IgM/IgG ratio greater than 1.2, while a secondary infection is indicated by a ratio less than 1.2. Test resultsA negative test for both IgM and IgG antibodies may indicate that the person doesn't have a dengue infection, or that the antibody levels are too low to detect.

Malaria antigen detection tests are a group of rapid diagnostic tests that detect proteins produced by malaria parasites in the blood of infected people. These tests can help diagnose malaria quickly, even when traditional laboratory techniques or equipment aren't available. Here are some things to know about malaria antigen tests: How they workMalaria antigen tests detect specific proteins released into the blood by the malaria parasite during its lifecycle. Different types of testsSome tests can detect only one species of malaria parasite, like Plasmodium falciparum or *P. vivax*, while others can detect multiple species. When to use themAntigen tests can show a positive result even in the early stages of infection, when antibody tests might still be negative. Importance of early diagnosisMalaria can lead to serious complications if left untreated, including kidney and liver damage, internal bleeding, and neurological problems. Common symptoms include high fever, chills, shivering, jaundice, nausea, vomiting, and convulsions