CALCA and infection: Synthesized by C-cells of the thyroid and various other tissues in response to bacterial toxins, PCT levels rise rapidly, usually within 2–3 h, and peak around 12–24 h after infection onset, with a half-life of approximately 22–35 h [36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54].