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Infectious‑disease surveillance has become an exercise in layered intelligence: each test adds a distinct dimension—speed, specificity, breadth—that together enable public health actors to detect, confirm, and monitor pathogens across time and space.



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1. The "speed" advantage of rapid tests


Rapid antigen or molecular assays can produce results within minutes. In the field—school screening, point‑of‑care clinics, airport gates—their immediacy turns a potential delay into an actionable moment. A single positive screen triggers isolation protocols before the patient even reaches a laboratory, preventing onward transmission that would otherwise occur while awaiting standard testing.



Because these assays do not require sophisticated instrumentation or extensive training, they are deployable in low‑resource settings where conventional diagnostics are impractical. The trade‑off is usually a lower sensitivity; still, for outbreak control, catching a fraction of cases early can outweigh the missed ones later.




2. Confirmatory Testing



What Is It?


Confirmatory testing employs highly specific, gold‑standard methods—such as PCR (polymerase chain reaction) or culture—to verify positive results obtained from screening tests. These methods have high sensitivity and specificity, providing definitive evidence of the presence of a pathogen.




Why Is It Important?




Accuracy: Reduces false positives that may arise from less specific screening assays.


Clinical Decision‑Making: Provides reliable data for diagnosis, treatment plans, and patient counseling.


Public Health Measures: Ensures correct identification of cases for contact tracing, isolation protocols, and epidemiological surveillance.




How Is It Used?


After a positive result in a screening test, confirmatory tests are performed. For instance:





A rapid antigen test indicating COVID‑19 infection is followed by an RT‑PCR assay.


An initial antibody test suggesting HIV infection is confirmed with Western blot or nucleic acid testing.







3. Comparing Screening Tests and Diagnostic (Confirmatory) Tests



Feature Screening Test Confirmatory/Diagnostic Test


Purpose Detect possible disease presence early; identify individuals needing further evaluation. Verify actual disease status; establish definitive diagnosis.


Sensitivity vs Specificity High sensitivity, lower specificity → minimize missed cases. Higher specificity (often ≥95%) and also high sensitivity → accurate diagnosis.


Cost & Turn‑around Cheaper, rapid, often point‑of‑care. More expensive, may require lab equipment or specialist interpretation; longer wait time.


False Positive/Negative Rates Acceptable false positives (to be followed up). False positives must be minimized to avoid unnecessary treatment.


Examples Rapid strep test, pregnancy tests, HIV rapid screening. PCR confirmation of viral infection, blood culture for bacteremia, confirmatory imaging.


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3. Practical Tips When Choosing an Assay



Situation Recommendation


Low disease prevalence Use a highly specific assay to avoid many false positives.


High stakes (e.g., cancer diagnosis) Prefer assays with very high sensitivity; consider combining multiple markers or using confirmatory tests.


Resource‑limited setting Select an assay that is affordable, requires minimal equipment and training, even if it sacrifices some performance metrics.


Research/early‑stage discovery Initially use a broad screening platform (e.g., proteomics) to identify potential biomarkers; later develop targeted, high‑performance assays for validation.


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3. Practical "Checklist" for Choosing an Assay




Define the clinical objective


- Screening? Diagnosis? Prognosis? Treatment monitoring?



Determine required performance thresholds (sensitivity, specificity, LOD) based on the above.



List available assay formats and map their intrinsic strengths/weaknesses to your requirements.



Assess technical feasibility:


- Sample type & volume

- Laboratory equipment & expertise

- Turn‑around time





Consider regulatory status (CE‑mark, FDA approval) if the assay will be used clinically.



Budget for consumables and instrument amortization.



Pilot a small validation study comparing the chosen format to a reference method.



Finalize selection: choose the format that best balances performance, practicality, and cost.







Quick‑reference decision matrix (for 4–10 µg total protein)



Requirement Ideal Format Practical Example


Highest sensitivity for low‑abundance proteins Western blot (high‑affinity primary + HRP/chemiluminescence) Standard WB with enhanced chemiluminescence kit


Simpler, rapid screening ELISA (commercial kits) Plate‑based ELISA using capture antibody


Multiplex detection of several proteins Luminex bead assay or multiplex ELISA 8–10 cytokine panel on Luminex platform


Semi‑quantitative relative abundance Flow cytometry (if cell surface marker) FACS analysis of surface antigens


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4. Practical "What‑to‑Do" Checklist



Step What to Do Why It Matters


Sample Prep Thaw at 37 °C, centrifuge, resuspend in PBS (or appropriate buffer). Keep on ice. Ensures viability and consistent antibody binding.


Blocking Incubate with Fc block (e.g., anti‑CD16/32) for 10 min at 4 °C. Prevents non‑specific Fc receptor engagement, especially important in NK cells or myeloid populations.


Antibody Panel Prepare master mix of all fluorochrome-conjugated antibodies plus viability dye. Titrate each antibody if needed. Guarantees optimal signal-to-noise; reduces spillover.


Staining Add antibody mix, incubate 20–30 min at 4 °C in the dark. Avoid washing until after staining unless required by protocol (e.g., for live/dead dye). Maintains fluorescence integrity and reduces background.


Washing Wash cells once with cold PBS + 2% FBS or directly fix if using intracellular markers. Use gentle centrifugation (