The Specificity of a Diagnostic FDG-PET Study Is a Function of the Patient and the Location

The present paper is based on the observations that 1) there is reported variation in the specificities according to the type of tumor targeted (target) by FDG PET and 2) that while one can posit that the sensitivity of the tracer depends on the avidity for glucose and the plasma supply of the target, even so that the targeting cannot influence the avidity of unrelated tissues or lesions. The hypothesis to be tested is twofold: 1) patients imaged for different types of lesions could have a different prevalence of FDG avid tissues or lesions different from the target and 2) that the target lesions could be generally located in body location (sites) more likely to contain unrelated foci of increased uptake. Variance analysis shows that the sensitivity varies according to the target (p = 0.022), but not according to the location (p = 0.34); the specificity varies with the location (p = 0.0012) and the target (p = 0.05). Specificities are significantly different in different primary targets and target locations. The former is assumed to be due to different comorbidities in patients with different targets, the latter to the different locations of unrelated glucose avid organs or structures. Conclusion: When specificities are recorded or defined, the patient population characteristics and the organ or pathology of the false positives should also be described.