Avidin and 111In-labelled biotin scan: A new radioisotopic method for localising vascular graft infection

Objectives:To evaluate a new imaging technique, for diagnosis of prosthetic vascular graft infection. Avidin is a protein which accumulates nonspecifically at sites of inflammation or infection. Due to its extremely low dissociation constant with biotin sites of infection can be imaged, using avidin as a pre-target, followed by injection of 111In-labelled biotin. This technique is much simpler than the common scintigraphic methods which employ labelling of blood components and its target-to-background ratio is greater than the methods employing radiolabelled proteins.Design:Prospective clinical study.Setting:A single department of vascular surgery and one of nuclear medicine of a Northern Italian hospital.Materials:Between May 1993 and May 1994, 31 grafts in 26 patients were studied; the series included 23 men and three women with a mean age of 65.5 years (range 54–76 years). The prosthetic graft (Dacron-16, ePTFE-15) were: aortoaortic 5, aortobifemoral 15, aortoiliac 1, and femoropopliteal 10. Sixteen patients were suspected of having a vascular graft infection (Group A), the other 10 patients served as controls (Group B). 20 mg of Avidin were injected iv, followed 24 h later by i.v. injection of 500 μg of Biotin labelled with 74 MBq of 111In.Chief outcome measures:Whole-body imaging was performed at 10 min and 2 h post-injection, along with SPECT imaging when indicated. Scan results were correlated with the traditional imaging modalities and the clinical outcome of the patients.Main results:In Group A: two patients (three grafts) were excluded from the study, there were six true-positives, one false-positive and 11 true-negatives. Results in Group B: 10 true-negatives. The overall sensitivity was 100%, the specificity 95%, the accuracy 96%, the positive predictive value 86% and the negative predictive value 100%.Conclusions:These data suggest that Avidin/111In-labelled Biotin scintigraphy is a useful non invasive diagnostic method for early diagnosis of suspected prosthetic vascular graft infection