CALCA and empyema: Falsely low PCT in localized infections like cellulitis, appendicitis, abscess and empyema can be misleading.30, 61-63 However, some data shows a modest performance of PCT in differentiating para-pneumonic effusion from malignant or transudative effusions.64 Interpretation of PCT levels can be difficult in patients with severe trauma, major burns, multi-organ failure, islet cell tumors and medullary thyroid carcinoma.