Can inflammatory markers and clinical indices serve as useful referral criteria for leukocyte scan with inflammatory bowel disease?

Background: In the follow-up of patients with inflammatory bowel disease (IBD), Tc-99m-HMPAO labelled leukocytes scintigraphy (leukocyte scan; LS) has long been established as a valuable diagnostic tool. The aim of this study was to estimate the relationship between scintigraphic results, inflammatory markers (IM) (including white blood cells (WBCs) and C-reactive protein (CRP)), clinical parameters and clinical indices of the disease activity (CI), in order to determine clinical settings in which LS is indicated.

Materials and methods: A total of 147 patients who underwent LS, (79 males, 68 females, median age 36), were examined from April 2010 until December 2017 at the University Hospital Centre Zagreb, Croatia. Among these, 126 (86%) had Crohn's disease (CD) and 21 (14%) had ulcerative colitis (UC). Either increased IM (either WBCs ≥10x109/L and/or CRP ≥7.4 mg/L) and/or CI, Crohn's disease activity index (CDAI) score ≥220 points, Harvey-Bradshaw index (HBI) score ≥8 points, and severe colitis defined according to Truelove and Witts' criteria (TWC) for UC, respectively, were considered consistent with active disease.

Results: Eighty-two patients (56%) had negative scans, while in 65 (44%) the scans were positive. Positive correlations were found between LS and all of the 3 parameters, WBCs, CRP and CI. When combined, the 3 parameters demonstrated even stronger positive correlation with the LS results with the correlation coefficient 0.76 (p<0.0001, 95% CI [0.68-0.82]). Using endoscopy and histological study findings of the obtained specimens as a composite reference standard, the overall sensitivity, specificity, positive predictive value and negative predictive value of IM and CI for LS were determined, being 91%, 85%, 83%, and 92%, respectively. IM and CI were both negative in 76 (52%) out of the total subjects. Of these, 70 had negative LS as well.

Conclusion: In the presence of normal IM with CI pointing to no active or mildly active disease, LS is not necessarily indicated.