Scientific Session 09 — Gastrointestinal - Diffuse Liver DiseaseTuesday, May 2, 2017
2465. Defining an Optimal CT Liver Attenuation Threshold to Screen for Hereditary Hemochromatosis
Lawrence E*, Pooler B, Pickhardt P. University of Wisconsin School of Medicine and Public Health, Madison, WI
Address correspondence to E. Lawrence (firstname.lastname@example.org)
Objective: The purpose of this study was to evaluate a liver attenuation threshold on unenhanced CT that would allow reasonably sensitive and specific detection of unsuspected hereditary hemochromatosis.
Materials and Methods: To establish the normal distribution of liver attenuation and test-positive rates of various thresholds, hepatic ROI attenuation measurements were performed in 3357 consecutive asymptomatic adults (mean age, 57.0 years) undergoing CT colonography (CTC) screening. To assess sensitivity, right and left hepatic attenuation were measured on unenhanced CT in 12 patients with genetically confirmed hemochromatosis (mean age, 48.3 years), including three cases detected on screening CTC. The inclusion criteria for the hemochromatosis cohort consisted of homozygous state for C282Y mutation of HFE gene, clinical diagnosis of hemochromatosis, and unenhanced CT performed before prolonged treatment. Fifteen patients were excluded because of a compound heterozygous state (n = 5) or lack of unenhanced CT (n = 10).
Results: Mean liver attenuation ± SD in asymptomatic adults was 59.4 ± 12.7 HU, compared with 78.7 ± 13.1 HU (range, 59–105 HU) in the hemochromatosis cohort. The test-positive rates for triggering a blood draw for ferritin (iron) testing in the screening cohort were 30.6% (n = 1028) at 65 HU, 8.2% (n = 275) at 70 HU, 1.2% (n = 39) at 75 HU, and 0.2% (n = 7) at 80 HU. The sensitivities for identifying hemochromatosis using these escalating liver attenuation thresholds were 83.3% at 65, 70, and 75 HU and 50.0% at 80 HU.
Conclusion: Our results indicate that an unenhanced CT liver attenuation threshold of 75 HU would be both sensitive (83%) and specific (~99%) for the detection of clinically relevant hereditary hemochromatosis. An unexplained liver attenuation at 75 HU (seen in ~1% of our adult screening population) should trigger appropriate laboratory investigation, since early intervention with phlebotomy can prevent significant organ damage.