Specificity of 99mTc-UBI for detecting infection foci in patients with fever in study

Fever of unknown origin (FUO) represents a challenge to clinical medicine, and bacterial cultures have been considered the 'gold standard' in discriminating between fevers resulting from bacterial infection and sterile inflammations. In nuclear medicine, a synthetic radiolabeled antimicrobial peptide (Tc-UBI) is used to image the molecular localization of infectious microorganisms.

The aim of this research was to determine the absolute and relative frequencies of Tc-UBI, by molecular imaging, to detect infection foci in patients with fever in study or FUO.

Images (207) from 196 patients with FUO acquired with Tc-UBI and a Siemens gammacamera were read by two nuclear medicine physicians and classified as positive or negative for infection foci. The diagnostic value was corroborated with our gold standard, which comprises bacterial cultures of biopsies, blood and urine, plus laboratory studies, morphological images (radiographs, nuclear magnetic resonance, computed tomography) and the clinical history of each patient. The absolute and relative frequencies of Tc-UBI were calculated from the molecular images versus the gold standard.

The specificity of Tc-UBI for localizing infection foci and for discarding sterile inflammation was 95.35%, the sensitivity was 97.52%, the positive predictive value was 96.72%, the negative predictive value was 96.47%, the accuracy was 96.62%, and the observed agreement between the bacterial culture and the molecular image was 96.62% (P=0.0001).

Considering that the absolute and relative frequencies are very high, we propose that, in the future, Tc-UBI molecular imaging could be the gold standard to detect infection sites and to discard sterile inflammation.