Influenza, antibiotics, and procalcitonin

Sure, I know what procalcitonin is, namely that which is not yet but will be calcitonin or the hormone produced by the thyroid which shuts off bone breakdown. Salmon calcitonin (Miacalcin) nasal spray used to be the only drug available for treatment of osteoporosis before Sally Field and other aging baby boomers elevated this condition to a status worthy of new and better compounds.

So what's this got to do with antibiotics? Nothing that we knew about back when I was in med school, I can assure you of that. An article and editorial in a September issue of JAMA(1), therefore, was quite an eye-opener on just how important it is to continue on with continuing medical education.

First, a word or two about lower respiratory tract infections (LTRI) and antibiotic use, a subject that impacts my patients and my decision-making processes every day, especially as swinish flu slams the Denver area. Why do I closet myself several times an hour with some miserable coughing wretch at great personal risk to my own lower respiratory tract? To distinguish ordinary, show-stopping/week-ruining influenza from its many complications, particularly secondary bacterial bronchitis and pneumonia. Often it's me (don't want to overprescribe antibiotics to avoid complications to the patient and antibiotic resistance to the public) vs. them (No time for this! Need antibiotics! Big test/presentation/trip/wedding coming up! Need antibiotics!).

I check out: how sick are they, how long have they been sick, are they having trouble breathing, is their O2 level low, how do their lungs sound, what color are their secretions. Knowing all the while that they feel miserably sick, any days with flu are too many days, their airways are swollen so of course they feel short of breath, and, of course, their secretions are doubtless gross because flu-sloughed cells in the airway plus gobs of white cells will make that which they hack out green.

Surely there must be a better formula other than my experience + intuition + observations. Enter procalcitonin(PCT), and it's not just for regulating calcium anymore. While the thyroid C-cells make PCT and turn it into calcitonin depending on the biochemical need to drop calcium levels in the blood, all sorts of other tissues release PCT when the body is fighting bacterial attack. Under normal conditions, PCT is barely detectable in the blood but levels can soar 100,000-fold with widespread sepsis as bacteria invade the bloodstream.

So here we have a wonderful demonstration of theragnostics (another concept that's new to me) wherein a diagnostic test--say PCT levels--identifies patients likely to be helped by a certain therapy, and then targeted drug therapy is given--e.g.antibiotics--based on those results. And I, with my expensive cognitive skills, am cut out of the equation thus making therapy not only more scientific and less intuitive, but also more accessible and affordable!

Now of course this is not yet anything you'll find in a Walgreen's TakeCare Clinic (until perhaps a handheld PCT-O-Meter is developed) but the possibilities are exciting. Not only could we know just when to treat acute bronchitis or pneumonia with antibiotics because PCT levels indicate a bacterial source, we could use this test in other puzzling situations such as whether or not artificial joints are infected or a patient with worsening chronic lung disease has an infectious complication.
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1) Schuetz, P et al. Effect of Procalcitonin-Based Guidelines vs Standard Guidelines on Antibiotic Use in Lower Respiratory Tract Infections. JAMA Sept. 9, 2009 Vol 302, No. 10 1059-1066.