biology

Viral disease testing

Viral disease testing is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Viral disease testing rather than just read about it. In short: Viral disease testing is the use of a variety of testing techniques for a variety of purposes, including diagnosing conditions, assessing immunity and understanding disease prevalence. The primary approaches include DNA/RNA tests, serological tests and antigen tests.

Key takeaways

Viral disease testing belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Viral disease testing to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Viral disease testing from memory before moving on to harder problems.

Reference excerpt

Viral disease testing is the use of a variety of testing techniques for a variety of purposes, including diagnosing conditions, assessing immunity and understanding disease prevalence. The primary approaches include DNA/RNA tests, serological tests and antigen tests.

History

COVID-19 In March 2020, Abbott received emergency use authorization (EUA) for its isothermal nucleic acid test for COVID-19. It produces test results in 5 minutes using its ID NOW portable testing system. It also received EUA for its m2000-based laboratory nucleic acid test for COVID-19. In April 2020, Abbott received EUA for its ARCHITECT IgG laboratory antibody test for COVID-19. Also in April, Abbott's ID NOW test was reported to have sensitivity of 85.2%. A later study found sensitivity of only 52%, inducing the FDA to issue an alert. A different study found sensitivity of 91%. The UK spent $20 million for antibody tests that proved flawed. In May 2020, a rapid antigen test from Quidel Corporation received EUA for detecting SARS-CoV-2. Test results were said to be available at point of care within 15 minutes. Sensitivity is 85%. Also in May 2020, a CRISPR genetic test was approved for emergency use that claimed 100% selectivity and 97.5% sensitivity. That month Abbott received EUA for its Alinity antibody test for COVID-19. The company claimed 100% sensitivity and 99.6% specificity for patients tested 14 days after symptoms began. Another review found that the accuracy of PCR tests depended on the interval between the infection and the test. Immediately after infection, the sensitivity was 0, rising to 80% after three days and then declining thereafter. In May 2020 the FDA withdrew approval for 29 of 41 antibody tests for which it had given EUAs.

Types

DNA/RNA tests Tests for viral DNA can look for either DNA or RNA. They typically use reverse transcriptase polymerase chain reactions to multiply the amount of genetic material in a small sample into an amount that is measurable. The genetic material is generally taken from the nose/sinus. One study found clinical sensitivity was found to range from 66 to 80%. Another found accuracy of 70%. A newer form uses CRISPR to produce a test result without requiring lab equipment. The test reacts with genetic material to produce a visible signal without requiring amplification.

Serological tests Serological tests look for the presence of antibodies in a test sample. Antibodies are materials that the body produces to fight off an infection. The primary antibodies sought in viral testing are IgE and IgG.

Rapid antigen tests A rapid antigen test quickly searches for antigens, protein fragments that are found on the surface of or within a virus. Antigen tests can be analyzed within a few minutes. Antigen tests are less accurate than PCR tests. It has a low false positive rate, but a higher false negative rate. A negative test result may require confirmation with a PCR test. Advocates claim that antigen tests are less expensive and can be scaled up more rapidly than PCR tests. Antigen tests are available for a variety of conditions, including streptococcus, influenza, giardia, Ebola and Helicobacter pylori. Antigens can be detected via blood, urine or stool.

Imaging Imaging such as computerized tomography can be used to inform a diagnostic process. CT scans are considerably more expensive than nucleic acid tests and involve a small dose of radiation. For COVID-19, they are seen as the most accurate diagnostic tool, because the disease creates patchy "ground glass" areas in the lungs that are revealed by a scan. One study found 97% sensitivity.

Accuracy Accuracy is measured in terms of specificity and selectivity. Test errors can come false positives (the test is positive, but the virus is not present) or false negatives (the test is negative, but the virus is present).

Sensitivity Sensitivity indicates whether the test accurately identifies whether the virus is or is not present. A 90% sensitive test will correctly identify 90% of infections, leaving 10% with a false negative result.

Specificity Specificity indicates how well-targeted the test is to the virus in question. Highly specific tests pick up only the virus in question. Non-selective tests pick up other viruses as well. A 90% specific test will correctly identify 90% of those who are uninfected, leaving 10% with a false positive result.

Worked examples

Example 1 — a first encounter with Viral disease testing

Start with the simplest possible case. Write down what Viral disease testing claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Viral disease testing before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Viral disease testing ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Viral disease testing

In research: Viral disease testing appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Viral disease testing in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Viral disease testing is common in secondary-school and first-year university syllabi. It links to neighbouring topics COVID-19 testing, Infectious disease blood tests, Viral diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Viral disease testing outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Viral disease testing in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Viral disease testing means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Viral disease testing out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Viral disease testing in simple terms?

Why does Viral disease testing matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Viral disease testing?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Viral disease testing.