“I told you I was sick”

Patient: “I have just come back from Bali and I have a fever and joint pains.”

Doctor: “Not to worry, I think you might have Dengue. I will do a blood test now, and another one in a month’s time to see if I am right.”

Patient: “Just a month, oh, it can’t be too serious then…”

Doctor: “No, it’s just Dengue, and what’s more I have some good news for you, I have just got some results back from the laboratory, that other illness you had 6 weeks ago turned out to be Legionella after all.”

Patient: “I told you I was sick…”

Even in the molecular age, it is surprising how often acute and convalescent serological testing is still utilised in clinical practice. Acute and convalescent serology is still frequently used for Legionella diagnosis, Dengue and other arboviruses, Lyme disease, Leptospirosis, the list goes on…

There are several potential reasons for this:

  • Requestor is used to ordering acute and convalescent serology-This is what the requestor has been doing for the past 30 years. Why change now?
  • Requestor is not aware that other options are available.- The requesting clinician may not be aware of the other options that are available for that particular condition, e.g PCR, antigen testing, etc.
  • Requestor scared/unaware they are allowed to order more “exotic” tests.- I find this a particular challenge when dealing with requests from the community setting. “I didn’t realise we were allowed to request a PCR test for this condition.”
  • Alternatives perceived to be more expensive.- And they are to a certain extent, particularly for arboviruses, but less so for Legionella. But don’t forget that 2 sets of serology along with the time for labour, interpretation and reporting is not an insignificant cost by any means.
  • Laboratory continues to offer acute and convalescent serology.- The laboratory can be guilty too, of not placing appropriate restrictions on acute and convalescent serology. The lab managers and clinical microbiologists of today are often  from an era where acute and convalescent serology was a mainstay of “diagnosis”.

If you were building a microbiology laboratory from scratch, and compiling a schedule or menu of tests, I would like to think acute and convalescent serology would be very low on the priority list.

There may be Public Health reasons why you might want to (retrospectively) confirm the diagnosis with acute and convalescent serology, but if this is the case, then it should be requested (or approved by) by Public Health doctors.

However for the purposes of acutely diagnosing the patient, by the time you get the result, the patient has either recovered, or not recovered…

Better to carefully restrict access to acute and convalescent serology, and “push” requestors into trying to make a real time diagnosis with more modern tests. The patient will thank you for it…



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