CALCA and bacterial infectious disease: Procalcitonin (PCT) levels can be challenging to interpret in patients with comorbidities because conditions such as massive stress, medullary thyroid carcinoma, and small-cell lung cancer can elevate PCT levels even in the absence of bacterial infection.20 PCT levels are also frequently elevated in patients with renal dysfunction in the absence of disease.21 Interestingly, the PCT half-life is similar in patients with and without renal dysfunction, approximately 28.9 hours in those without renal dysfunction and 33 hours in those with dysfunction.