Medical Fun Facts Podcast

MFF0044: Serology

If I’ve timed this correctly, tonight’s show is dropping on Thursday 2 March 2017.

So, what is serology? I’m going to confine myself to describing serology in clinical microbiology. Serology is a technique used to diagnose infections and determine the cause of an infection. In days gone by, especially with some hard to grow viruses and some fastidious or dangerous bacteria, serology was the best way to make a diagnosis. That said, serology is an indirect method of diagnosis. You make a series of assumptions when using serology to diagnose an infection. In clinical microbiology circles, it’s often said that serology can be as much art as it is science.

Serology is the detection of antibodies to antigens which are associated with pathogenic microorganisms. Take for example my first exposure to clinical microbiology. It was 1982 and I was in grade 12 at high school. I had been given permission from a local private pathology practice to undertake an experiment where I compared three different serological techniques to quantify the amount of antibody mice made to rubella virus vaccine. Around that time there had been some questions about the quality of the vaccine being used in the national program and questions had been asked about the tests being used. I compared hæmagglutination inhibition, FIAX and enzyme-linked immunosorbent assay (ELISA). It turns out each method was comparable but the ELISA fitted in better with the laboratory work flow. Each of these methods used different approaches to detect the presence of antibody and to also do an additional step of quantifying the antibody.

Not only can serology be used to diagnose an infection, for some situations, measuring the antibody can indicate if a person is immune or susceptible to an infection. If we go back to rubella, if you’ve had the infection, we would expect a brisk antibody reaction and quite a high titre of antibody. If you’ve been immunised with a commercial vaccine, we also expect to see the development of antibody a few weeks after it’s been administered. If we don’t then we know the immunisation process hasn’t worked. If we test more people and discover they haven’t responded by producing antibody, we know we have a problem with the vaccine and a regulatory investigation is needed.

In some situations, it’s important to know if you’ve been exposed to an infection for the purposes of work. Take, for example, healthcare workers, Hepatitis B virus infection is important. Most healthcare workers will be offered vaccination if, after testing, antibodies to Hepatitis B virus surface antigen are not found. Being able to test for past exposure and determine immunity is important for the healthcare worker and for their patients.

The interpretation of serological results can also be problematic. Cross reactions are common and it takes time and experience to interpret the results. This is why specialisation in clinical medicine is important. I have no doubt that if a GP had training in medical laboratory science and was an experienced serologist, she or he could interpret results without the assistance from a pathologist. That is not usually the case. GPs are very good at what they do, the bulk of them along with most other medical practitioners would not be expert in interpreting serological results. I’m all for patients and their doctors having as much information as possible, but that should not be at the expense of wisdom.

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