Most diagnostic laboratories have now left viral culture behind, but a lot still have sizeable Infectious Serology departments.

However there are a lot of infections where molecular methodology now gives a more sensitive and specific diagnosis. Take for example measles, mumps, pertussis, and herpes simplex virus for starters.

In addition, for those infections that require the interpretation of both acute and convalescent serology, molecular methods are also a lot faster.

Looking at the more serious end of the spectrum of infectious diseases, for example the haemorrhagic fevers, leptospirosis, and some of the arboviruses such as Dengue, Zika and Chikungunya, a lot of clinicians are still used to diagnosing these conditions by serological means, because for a long time this was the only means available. However for a lot these conditions, PCRs are now available and it is a responsibility of the microbiology lab to educate requestors as to what is available locally in order to offer the most rapid and sensitive diagnosis for the (often sick) patient.

The molecular methodology may still be more expensive (the price is coming down all the time) but the cost benefit analysis for a lot of these conditions is starting to weigh more in favour of molecular.

There are two areas where Infectious serology is still well established and may well be for some time yet:

“Infectious mononucleosis” screens. In this area there is still a lot of serology performed for EBV, CMV and Toxoplasmosis. The serological tests for these pathogens are relatively cheap, and outwith the immunocompromised/pregnant cohort, of relatively low clinical importance.

Hepatitis & HIV Screening: The cost of Hepatitis A, B and C PCR tests is still quite significant, so I think serology will stick around in this area for a while yet. In addition for Hepatitis B serology there is quite a lot of information one can gleam from the serological pattern of results regarding the epidemiology, chronicity and time course of infection.

Despite the above I can only see Infectious serology departments gradually shrinking over the years, at the expense of expanding molecular departments.

Infectious serology has always been and always will be a bit of a dark art. I do foresee the time (and possibly during my career) when serological testing will be restricted only to confirming past infection/immunity and all acute infections will be diagnosed by molecular methods such as PCR.

I believe one of the roles of clinical microbiologists and senior scientists is to weigh up the cost-benefit analysis for each of the pathogens where infectious serology could be potentially replaced by molecular methods. Such changes may not always be popular, as funders may baulk at the costs and serology staff may see their jobs on the line, but that is part and parcel of creating a lab that is future-proofed….

Michael