The use of procalcitonin in the management of bacterial infections has recently received a lot of attention. A quick search of PubMed reveals more than 4000 hits in the last decade alone! Yet it's only just crept into my clinical practice. Perhaps the delay was due to too much research – too many conflicting results leading to a message that was hard to fathom. Or just as likely, it had never featured in my training or been used by those I've worked alongside. Nevertheless, in recent months I've started to use it in my day-to-day practise and thought this would be a good time to try and explain why!
Procalcitonin is the precursor of calcitonin, a hormone that is normally produced by the thyroid gland. Over the years researchers have found that the molecule is also produced by other parts of the body in response to a bacterial infection. Since it is far more specific than c-reactive protein (CRP), erythrocyte sedimentation rate (ESR) or white cell count (WCC), procalcitonin measurements are now becoming being widely used in guiding antibiotic prescribing.
A procalcitonin measurement can be obtained from a single blood sample (<5mls) and costs less than £25 to process. Results are available in just a couple of hours. Typically, procalcitonin levels peak within 24 hours of infection and fall quickly with treatment. This allows clinicians to not only use procalcitonin to initiate antibiotics but also to stop them when levels fall.
A table like this can be used to guide antibiotic prescribing in lower respiratory tract infection. Used appropriately, procalcitonin measurements have been shown to safely reduce drug use. This has far reaching implications - not only can it benefit patients by reducing the incidence and severity of side effects, but in the long term procalcitonin has the potential to reduce antibiotic resistance
So how can it be used in clinical practise? Rather than rely entirely upon a measurement to guide antibiotic prescribing, the answer is to use procalcitonin as part of a much wider clinical assessment. Here’s 2 recent cases where procalcitonin helped determine whether antibiotics should be administered...
A man in his 70’s with a background of chronic obstructive pulmonary disease (COPD) was admitted to hospital with symptoms of cough and breathlessness. His x-ray showed an area of lung collapse and inflammatory markers were raised. Despite being given 3 courses of antibiotics, his symptoms slowly worsened over 7 days and he was referred to HDU for high flow oxygen therapy and monitoring. On admission he tested positive for influenza A. Temperature 37.8C. CRP and WCC measurements were unchanged since admission. His procalcitonin measurement was 0.1ng/ml. Rather than continue, antibiotics were stopped and over the next few days the patient went on to make a complete recovery.
A woman in her 40’s with a history of gall stone disease presented with an episode of pancreatitis. She was found to have low blood pressure (70/30) and admitted to HDU for vasopressor support and monitoring. In the Emergency Department she had received a dose of antibiotics. CRP and WCC were mildly elevated. Temperature 37.2C. Blood cultures were negative. CT scanning revealed an inflamed pancreas with no evidence of necrotic damage. Her procalcitonin measurement was 0.1ng/ml. Antibiotics were stopped and the patient recovered quickly following the passing of a gallstone.
In each of these cases procalcitonin was used alongside a number of other tests, observations and measurements to determine whether a bacterial infection was present. You might argue that there was enough evidence in both cases to decide that antibiotics were not needed. You're probably right! But in these cases the procalcitonin concentration made the decision making process a lot easier. The last thing any clinician wants to do is discontinue antibiotics if the patients need them.
Is there a role for accurately identifying bacterial infections in a remote mountain environment? Of course there is! We all want to know whether a Khumbu Cough is caused by a bacterial infection or persistent diarrhoea needs antibiotics. In recent years, there has been a growing demand from clinicians for point of care testing and the medical technology industry has responded. Several procalcitonin tests are now available. These range from a simple lateral immunoassay test strip that provides a positive (>0.1ng/ml) or negative result, to more sophisticated battery powered, hand held devices that provide definitive measurements in minutes.
In the Biopanda Rapid PCT Test two drops of blood are mixed with 1 drop of buffer solution in a specimen well. The mixture migrates along the test strip by capillary action and comes into contact with a procalcitonin antibody lined membrane
The presence of procalcitonin (>0.1ng/ml) produces a coloured line (T). A second coloured line always appears in the control (C) indicating that sufficient volume has been added. Results are available in 15 minutes
Access to procalcitonin measurement is clearly increasing. When used together with other tests, observations and measurements, this has the potential to transform the diagnosis and treatment of bacterial infection - not only in our day-to-day practise but in the mountains as well!
Postscript - it's worth saying that procalcitonin has been very useful in the management of patients with suspected Covid-19. In the past - when it would have been difficult to distinguish between a bacterial and viral infection - many of these patients would have received antibiotics for 7 or more days. Now with procalcitonin testing, clinicians have been able to distinguish between these organisms and prescribe far fewer antibiotics.