Widal Test (Tube Test)

Collect venous blood into a plain (red-top) tube or a serum‑separator tube (SST, gold/yellow top) that contains no anticoagulant. Allow the sample to clot, centrifuge, and use the separated serum for the Widal agglutination test. Avoid anticoagulated tubes (EDTA, citrate, heparin), as they prevent proper clotting and can interfere with serological agglutination results.

The Widal tube test reports agglutination titers against Salmonella antigens: O (somatic) and H (flagellar), often for Typhi and Paratyphi. Results appear as dilutions (e.g., 1:40, 1:160). A fourfold rise between acute and convalescent samples or a single high titer (region-specific cutoff, commonly ≥1:160) suggests infection. Interpret with clinical context and local cutoffs; cross-reactions limit specificity.

Perform serial twofold dilutions of patient serum in labeled tubes. Add equal volumes of standardized antigen suspension to each tube, include positive and negative controls, mix gently, and incubate (usually 37°C for 1–2 hours). After incubation, examine tubes for visible agglutination; the highest serum dilution showing definite clumping is the antibody titre. Use aseptic technique and repeat ambiguous results for confirmation.

Typhidot is performed on serum or whole blood. For laboratory testing, collect blood in a plain red‑top tube or serum‑separator tube (SST) to obtain serum. For rapid/point‑of‑care use, EDTA or heparinized tubes (or capillary finger‑stick blood) can be used. Process promptly: allow clotting, centrifuge to separate serum, avoid hemolysis, and refrigerate specimens if testing is delayed.

ELISA (enzyme-linked immunosorbent assay) is used to detect and quantify specific proteins, antigens, or antibodies in blood and other fluids. Common applications include diagnosing infections (e.g., HIV and other viral serology), measuring hormones and biomarkers, monitoring vaccine-induced immune responses, and screening for autoimmune disorders. It’s widely used in clinical diagnostics, epidemiology, and biomedical research for its sensitivity and scalability.

For a Widal tube agglutination test, patient serum is serially diluted in saline or a suitable buffer using doubling dilutions (for example 1:20, 1:40, 1:80, 1:160). Each dilution is combined with standardized Salmonella O and H antigens; visible agglutination indicates antibodies. The highest dilution showing agglutination is reported as the titre. Perform testing in a qualified laboratory with proper controls.