be useful against covid-19, others have argued that antigen tests are highly sensitive when viral load is high and people are contagious, making them suitable for public health screening. routine antigen tests can quickly identify when asymptomatic people are contagious, while follow-up pcr can be used if confirmatory diagnosis is needed. antibody tests left: automated analyzer for immunoassays, used, for example, to find sars-cov-2 antibodies. right: example of quantitative results for sars-cov-2 antibody test. the body responds to a viral infection by producing antibodies that help neutralize the virus. blood tests (also called serology tests or serology immunoassays) can detect the presence of such antibodies. antibody tests can be used to assess what fraction of a population has once been infected, which can then be used to calculate the disease's mortality rate. they can also be used to determine how much antibody is contained in a unit of convalescent plasma, for covid-19 treatment, or to verify if a given vaccine generates an adequate immune response. sars-cov-2 antibodies' potency and protective period have not been established. therefore, a positive antibody test may not imply immunity to a future infection. further, whether mild or asymptomatic infections produce sufficient antibodies for a test to detect has not been established. antibodies for some diseases persist in the bloodstream for many years, while others fade away. the most notable antibodies are igm and igg. igm antibodies are generally detectable several days after initial infection, although levels over the course of infection and beyond are not well characterized. igg antibodies generally become detectable 10–14 days after infection and normally peak around 28 days after infection. this pattern of antibody development seen with other infections, often does not apply to sars-cov-2, however, with igm sometimes occurring after igg, together with igg or not occurring at all. generally, however, median igm detection occurs 5 days after symptom onset, whereas igg is detected a median 14 days after symptom onset. igg levels significantly decline after two or three months. genetic tests verify infection earlier than antibody tests. only 30% of those with a positive genetic test produced a positive antibody test on day 7 of their infection. rapid diagnostic test (rdt) rdts typically use a small, portable, positive/negative lateral flow assay that can be executed at point of care. rdts may process blood samples, saliva samples, or nasal swab fluids. rdts produce colored lines to indicate positive or negative results. enzyme-linked immunosorbent assay (elisa) elisas can be qualitative or quantitative and generally require a lab. these tests usually use whole blood, plasma, or serum samples. a plate is coated with a viral protein, such as a sars-cov-2 spike protein. samples are incubated with the protein, allowing any antibodies to bind to it. the antibody-protein complex can then be detected with another wash of antibodies that produce a color/fluorescent readout. neutralization assay neutralization assays assess whether sample antibodies prevent viral infection in test cells. these tests sample blood, plasma or serum. the test cultures cells that allow viral reproduction (e.g., vero e6 cells). by varying antibody concentrations, researchers can visualize and quantify how many test antibodies block virus replication. chemiluminescent immunoassay chemiluminescent immunoassays are quantitative lab tests. they sample blood, plasma, or serum. samples are mixed with a known viral protein, buffer reagents and specific, enzyme-labeled antibodies. the result is luminescent. a chemiluminescent microparticle immunoassay uses magnetic, protein-coated microparticles. antibodies react to the viral protein, forming a complex. secondary enzyme-labeled antibodies are added and bind to these complexes. the resulting chemical reaction produces light. the radiance is used to calculate the number of antibodies. this test can identify multiple types of antibodies, including igg, igm, and iga. neutralizing vis-à-vis binding antibodies most if not all large scale covid-19 antibody testing looks for binding antibodies only and does not measure the more important neutralizing antibodies (nab). a nab is an antibody that neutralizes the infectivity of a virus particle by blocking its attachment to or entry into a susceptible cell; enveloped viruses, like e.g. sars-cov-2, are neutralized by the blocking of steps in the replicative cycle up to and including membrane fusion. a non-neutralizing antibody either does not bind to the crucial structures on the virus surface or binds but leaves the virus particle infectious; the antibody may still contribute to the destruction of virus particles or infected cells by the immune system. it may even enhance infectivity by interacting with receptors on macrophages. since most covid-19 antibody tests return a positive result if they find only binding antibodies, these tests cannot indicate that the subject has generated protective nabs that protect against re-infection. it is expected that binding antibodies imply the presence of nabs and for many viral diseases total antibody responses correlate somewhat with nab responses but this is not established for covid-19. a study of 175 recovered patients in china who experienced mild symptoms reported that 10 individuals had no detectable nabs at discharge, or thereafter. how these patients recovered without the help of nabs and whether they were at risk of re-infection was not addressed. an additional source of uncertainty is that even if nabs are present, viruses such as hiv can evade nab responses. studies have indicated that nabs to the original sars virus (the predecessor to the current sars-cov-2) can remain active for two years and are gone after six years. nevertheless, memory cells including memory b cells and memory t cells can last much longer and may have the ability to reduce reinfection severity. a point of care test in peru. a blood droplet is collected by a pipette. blood from pipette is then placed onto a covid-19 rapid diagnostic test device. the rapid diagnostic test shows reactions of igg and igm antibodies. the left tray shows a negative result, and the right positive sniff tests sudden loss of smell can be used to screen people on a daily basis for covid-19. a study by the national institutes of health showed that those infected with sars-cov-2 could not smell a 25% mixture of ethanol and water. because various conditions can lead to the loss of the sense of smell, a sniff test would not be definitive but indicate the need for a pcr test. because the loss of the sense of smell shows up before other symptoms, there has been a call for widespread sniff testing. health care bureaucracies have generally ignored sniff tests even though they are quick, easy and capable of being self-administered daily. this has led some medical journals to write editorials supporting the adoption of sniff testing. imaging typical visible features on ct initially include bilateral multilobar ground-glass opacities with a peripheral or posterior distribution. covid-19 can be identified with higher precision using ct than with rt-pcr. subpleural dominance, crazy paving, and consolidation may develop as the disease evolves. chest ct scans and chest x-rays are not recommended for diagnosing covid-19. radiologic findings in covid-19 lack specificity. chest x-rays, computed tomography scans and ultrasounds are all ways the coronavirus disease can be detected. a chest x-ray is a portable lightweight machine. this machine is typically more available than polymerase chain reaction and computerized tomography scans. it only takes approximately 15 seconds per patient. this makes chest-x ray readily accessible and inexpensive. it also has quick turnaround time and can be crucial to the clinical equipment in the detection of coronavirus disease. computerized tomography scans involve looking at 3d images from various angles. this is not as available as chest x-ray, but still only takes about 15 minutes per patient. computerized tomography has been a known routine scanning for pneumonia diagnosis, therefore can also be used to diagnose coronavirus disease. computerized tomography scans may help with ongoing illness monitoring throughout treatment. patients who had low-grade symptoms and high body temperatures revealed significant lung indications on their chest computed tomography scans. they emphasized how important chest computerized tomography scans are for determining how serious the coronavirus disease infection is. ultrasound can be another tool to detect coronavirus disease. an ultrasound is a type of imaging exam that produces images using sound waves. unlike computerized tomography scans and x-rays, ultrasound does not use radiation. moreover, it is inexpensive, simple to use, repeatable, and has several additional advantages. using a hand-held mobile machine, ultrasound examinations can be performed in a variety of healthcare settings. there are some downsides to using imaging, however. the equipment needed for computed tomography scans is not available in most hospitals, making it not as effective as some other tools used for detection of the coronavirus disease. one of the difficult tasks in a pandemic is manually inspecting each report, which takes numerous radiology professionals and time. there were several problems with early studies of using chest computerized tomography scans for diagnosing coronavirus. some of these problems included the disease severity characters being different in severe and hospitalized cases. the criteria for doing a chest computerized tomography scan were not defined. there was also no characterization of positive chest computerized tomography scans results. the computerized tomography scans findings were not the same as positive computerized tomography scans findings of coronavirus. in a typical clinical setting, chest imaging is not advised for routine screening of covid-19. patients with asymptomatic to mild symptoms are not recommended to be tested via chest computerized tomography scans. however, it is still crucial to use, particularly when determining complications or disease progression. chest imaging also is not always the first route to take with patients who have high risk factors for covid. high risk patients that had mild symptoms, chest imaging findings were limited. although a computerized tomography scan is a strong tool in the diagnosis of covid-19, it is insufficient to identify covid-19 alone due to the poor specificity and the difficulties that radiologists may experience in distinguishing covid-19 from other viral pneumonia on chest computerized tomography scans. serology (colab score) tests the standard blood test (quick scan) taken at the emergency room measures different values. by use of the blood quick scan the colab score is calculated with a developed algorithm based on how the coronavirus causes changes in the blood. the software is intended for use in emergency rooms to quickly rule out the presence of the disease in incoming patients. a not negative result is followed by a pcr (polymerase chain reaction) or lamp (loop-mediated isothermal amplification) test. breath tests the breath test by a coronavirus breathalyzer is a pre-screening test for people who have no or mild symptoms of covid-19. a not negative result is followed by a pcr or lamp test. animals in may 2021, reuters reported that dutch researchers at wageningen university had shown that trained bees could detect the virus in infected samples in seconds and this could benefit countries where test facilities are in short supply. a two-month study by the necker-cochin hospital paris in conjunction with the french national veterinary school reported in may 2021 that dogs were more reliable than current lateral flow tests. researchers in paris in march 2022 reported in a preprint not yet peer-reviewed that trained dogs were very effective for rapidly detecting the presence of sars-cov2 in people, whether displaying symptoms or not. the dogs were presented with sweat samples to smell from 335 people, of whom 78 with symptoms and 31 without tested positive by pcr. the dogs detected 97% of the symptomatic and 100% of the asymptomatic infections. they were 91% accurate at identifying volunteers who were not infected, and 94% accurate at ruling out the infection in people without symptoms. the authors said "canine testing is non-invasive and provides immediate and reliable results.further studies will be focused on direct sniffing by dogs to evaluate sniffer dogs for mass pre-test in airports, harbors, railways stations, cultural activities or sporting events." functional assays tollotest is a molecular test that detects the activity of a sars-cov2 protease, which is a biomarker for active infection. history main article: development of covid-19 tests timeline of total number of tests in different countries in january 2020, scientists from china published the first genetic sequences of sars-cov-2 via virological.org, a "hub for prepublication data designed to assist with public health activities and research". researchers around the world used that data to build molecular tests for the virus. antigen- and antibody-based tests were developed later. even once the first tests were created, the supply