Can procalcitonin guide decisions about antibiotic management?
ROLE IN PROGNOSIS
In addition to being a useful marker for diagnosis of bacterial infections, the procalcitonin level has significant prognostic implications, as a high or persistently elevated level correlates with a higher rate of all-cause mortality.17 The prognostic capability may enhance triage decisions.
Because the procalcitonin level lacks specificity, clinicians need to be aware of noninfectious causes of elevations such as malignancy, surgery, impaired renal function,8 and myocardial infarction.18 In these scenarios, it is important to think critically about the procalcitonin result and consider an adjusted cutoff.
A study of procalcitonin to predict a positive blood culture in patients with renal disease suggested an optimal cutoff value of 1.06 ng/mL for patients with an estimated glomerular filtration rate of 30 to 60 mL/min/1.73m2, and a value of 2.50 ng/mL for a rate less than 30 mL/min/1.73m2.8
In a chronic process like malignancy, the procalcitonin level is usually not markedly elevated. But it can also remain persistently elevated, with no improvement associated with effective antibiotic treatment and no clinical deterioration associated with treatment failure.
Use of procalcitonin and troponin
For some patients, there may be diagnostic uncertainty about interpreting procalcitonin and troponin results, as both plaque-rupture myocardial infarction and demand ischemia from sepsis can cause elevation in both values. In a study of patients with acute myocardial infarction, the procalcitonin level peaked at 3.57 ng/mL and troponin peaked at 60 ng/mL at about 24 hours after admission.18 This suggests that a troponin-to-procalcitonin ratio may help distinguish acute myocardial infarction from demand ischemia, though the optimal cutoff is unknown.
Both troponin and procalcitonin levels can help rule out acute severe illness (eg, bloodstream infection, acute myocardial infarction). But both can be falsely negative in early presentation or in less severe disease (eg, localized infection, unstable angina), as well as in noninfectious inflammation and nonobstructive myocardial injury.
Both are important prognostic markers. Furthermore, both can be chronically elevated in patients with renal disease, but both still have a characteristic rise and fall in acute disease states. But neither should be used in isolation without information from electrocardiography, other tests, and the clinical context.
CAVEATS AND CHALLENGES
Based on clinical experience and reported studies, procalcitonin testing has proven valuable in the diagnosis, prognosis, and management of a range of diseases, particularly certain infections.
However, procalcitonin testing must be applied cautiously and judiciously. There is a potential for early false-negative results, and false-positive results can occur in conditions such as kidney disease, myocardial infarction, postoperative stress response, and malignancy, though there may be ways to factor these conditions into interpretation of procalcitonin results.
Widespread procalcitonin testing may lead to excessive costs, though the cost for each test is reasonable and probably offset by benefits of diagnostic clarification and decreased use of antibiotics, if appropriately applied.
The primary roles for procalcitonin testing are to rule out infection in patients with low probability of infection and to allow safe early cessation of antibiotic therapy in patients with presumed bacterial infection. Procalcitonin testing can enable providers to stop antibiotics safely, with the general trend showing decreased antibiotic utilization without patient harm. This can result in healthcare cost savings and improved patient outcomes such as decreased length of hospital stay, decreased readmission rates, fewer adverse effects from antibiotics, and possibly improved mortality rates.
Despite the potential benefits from procalcitonin testing, results must be interpreted within the clinical context because a host of factors can affect the values. Extreme values are more useful than intermediate values, which are difficult to interpret and have poor predictive value.
Although all current biomarkers for infection are imperfect, procalcitonin appears to have better diagnostic accuracy than other markers such as the white blood cell count and C-reactive protein in multiple clinical scenarios, and its appropriate use appears to improve important outcomes such as survival.
