The Cost Effectiveness of Endoscopic Ultrasound ( EUS ) Based Strategy in Diagnosis of Common Bile Duct Stones

Background: Multiple reports showed the efficacy of EUS comparable to ERCP in the diagnosis of CBD stone. The EUS-based strategy has provided the cost saving in diagnosis of CBD stone in patients with intermediate risk in previous studies in western population. There were multiple parameters involved the cost effectiveness analysis included cost of ERCP, cost of EUS, prevalence of CBD stones, the sensitivity and specificity of EUS and the rate of complications related to EUS and ERCP. These parameter may vary from center to center and from region to region.

Aims: To assess the cost effectiveness of EUS based strategy versus ERCP based strategy in diagnosis of CBD stones in patients with intermediate risk in a developing country.

Method : A prospective study in 141 patients with suspected CBD stones based on clinical, biochemical and imaging by trans-abdominal ultrasonography or computed abdominal tomography. All patients underwent EUS. All patients with high risk for CBD stone underwent ERCP after the EUS. For patients with intermediate risk for CBD stone, ERCP's were done at the discretion of the attending physicians. For patients with ERCP done, the diagnosis of CBD stone was confirmed by ERCP demonstration of CBD stone. In patients with intermediate risk without ERCP done, clinical follow up to assess biliary symptoms and liver function test as surrogated markers for CBD stone at 3 months interval for one year were done. The false negative rate in patients with EUS and ERCP done in this study was used to estimate the false negative rate in patients in clinical surrogated group.

Definition: High risk of CBD stones was defined when CBD stone was detected by US/CT or dilated duct with abnormal liver function test ( LFT ). Intermediate risk of CBD stones was defined when US/CT showed normal bile duct with abnormal LFT or dilated duct with normal LFT.

Cost analysis :The cost of making diagnosis of CBD stone excluding all costs of treatment was analyzed. The cost of all patients with suspected CBD stones undergoing ERCP was calculated and compared with the strategy of EUS follow by ERCP. The cost was evaluated by (1) mean costs of EUS and ERCP based on the actual cost in our center which included costs of medical staffs, disposable materials, drugs, equipment amortization and maintenance. (2) cost associated with complications induced by the procedure.

Statistical analysis: Test performance of the endoscopic ultrasound in diagnosis of CBD stones was analyzed with two by two tables. The sensitivity, specificity, positive and negative predictive values were calculated.