Serological Techniques: The science of detecting antigens (bacterial, viral, parasitic) or antibodies to antigens in blood serum.

The antigen-antibody reactions results in agglutination, neutralization or haemolysis.

When an antigen is exposed to an antibody in suspension in an appropriate concentration, they react.

The reaction can be a visible one, such as the formation of a precipitate made up of a complex of the antigen and the antibody

Rapid tests, also known as rapid diagnostic tests (RDTs), are easy-to-use tests that provide quick results, usually in 20 minutes or less. Unlike most standard tests, which have to be sent to a lab, rapid tests are done and provide results at the point of care. The point of care is the place where you are getting care. It can include your provider’s office, a clinic, or even your own home.

An antibody is a protein produced by the body’s immune system when it detects harmful substances, called antigens. Examples of antigens include microorganisms (bacteria, fungi, parasites, and viruses) and chemicals.

Antigen

Any substance that causes the body to make an immune response against that substance. Antigens include toxins, chemicals, bacteria, viruses, or other substances that come from outside the body.

agglutination

a reaction in which particles (as red blood cells or bacteria) suspended in a liquid collect into clumps and which occurs especially as a serological response to a specific antibody.

The incubation period is the number of days between when you’re infected with something and when you might see symptoms. Health care professionals and government officials use this number to decide how long people need to stay away from others during an outbreak.

window period

The time period that starts when a person becomes infected with the human immunodeficiency virus (HIV) and ends when the body makes enough antibodies against the virus or HIV DNA or RNA to be found with an HIV test.

Non Reactive

This means that the test did not find any evidence of infection.

Reactive

This means that the test did find any evidence of infection.

If a package has been open for some time before the RDT is used, the RDT may be damaged by heat or humidity and give an invalid (false) result. You should discard this package and use another, unopened, package.

They either detect antibody (Ab) or antigen (Ag) that an individual develops against the infection or the viral protein i.e. the antigen of the pathogen.

look for certain antibodies to see whether a person has been exposed to or infected with a virus or other infectious agent. Sometimes antibodies are made against the body’s own tissues.

Standard Operating Procedure (SOP)

An SOP is a procedure specific to your operation that describes the activities necessary to complete tasks in accordance with industry regulations, provincial laws or even just your own standards for running your business.

There are two types of rapid diagnostic test

1.Rapid antibody test

2.Rapid antigen test

Rapid antibody test

A rapid antibody test kit detects the presence of a patient-generated antibody that is produced in response to a certain infection.

Generally, IgG and IgM antibody isotypes are detected in this test.

IgM is an initial antibody that is produced against the infection whereas the IgG antibody appears later during the infection.

These antibodies are present in the blood sample when a person has an infection and gives a positive test result.

RAPID ANTIGEN TEST

Rapid antigen kit detects the presence of specific viral protein known as antigen which indicates the current viral infection.

This test is commonly used for the detection of respiratory pathogens like the influenza virus, respiratory syncytial virus (RSV), and coronavirus.

Some examples of serological tests are

Malaria Rapid Diagnostic Test (mRDT)

HIV rapid test

RPR

VDRL test

Widal test

RDTs are lateral flow immuno-chromatographic antigen-detection tests, which rely on the capture of dye-labelled antibodies to produce a visible band on a strip of nitro-cellulose, often encased in plastic housing, referred to as cassettes.

Inside the cassette is a strip made of filter paper and nitrocellulose. Typically, a drop of blood is added to the RDT through one hole (A; sample well), and then a number of drops of buffer usually through another hole (B; buffer well). Buffer carries the blood along the length of the RDT.

The first step of the test procedure involves mixing the patient’s blood with a lysing agent in a test strip or well. This ruptures the red blood cells, releasing more parasite protein.

Cont….

Dye-labelled antibody, specific for target antigen, is present on the lower end of nitrocellulose strip or in a plastic well provided with the strip. Antibody, also specific for the target antigen, is bound to the strip in a thin (test) line, and either antibody specific for the labelled antibody, or antigen, is bound at the control line.

Blood and buffer, which have been placed on strip or in the well, are mixed with labelled antibody and are drawn up the strip across the lines of bound antibody

If antigen is present, some labelled antibody-antigen complex will be trapped and accumulate on the test line. Excess-labelled antibody is trapped and accumulates on the control line. A visible control line indicates that labelled antibody has traversed the full length of the strip, past the test line, and that at least some free antibody remains conjugated to the dye and that some of the capturing properties of the antibodies remain intact.

The intensity of the test band will vary with the amount of antigen present, at least at low parasite densities (antigen concentration), as this will determine the amount of dye particles which will accumulate on the line. The control band intensity may decrease at higher parasite densities, as much of the labelled antibody will have been captured by the test band before reaching the control.

Cost; RDTs are generally cost-effective compared to other laboratory test, so it is affordable.

Time; RDTs provide results within few minutes and help in immediate initiation of treatment and can prevent further transmission.

Easy to train and easy to use; are always portable and does not required specialize laboratory equipment.

Effective tools for screening; RDTs are effective tools for screening individuals at risk of specific disease and also to monitor disease prevalence, track outbreaks and guide public health.

Little or no special equipment required. This is especially useful in areas with limited resources or access to specialized labs.

Disadvantages of rapid tests

Lower sensitivity than lab tests. Sensitivity means how well a test can identify a disease or condition. Rapid tests are not as good as lab tests at finding diseases in the earliest stages of infection.

False negatives are more common. A false negative result means your test shows you don’t have a disease or condition, but you actually do have it.