Predictive Value of Ultrasonography and Alkaline Phosphate (ALP) in Common Bile Duct (CBD) Stones.

Objective: To assess the predictive performance of trans‑abdominal US (TAUS) and serum ALP for detecting CBD stones in adults by taking MRCP as the reference standard. Study Design: Prospective Cross-validation study. Setting: Department of Gastroenterology, Kulsoom Bai Valika Hospital, Karachi, Pakistan. Period: Oct 2024 to Apr 2025. Methods: Adults (≥ 18 years) with clinical suspicion of common bile duct stones underwent TAUS (2–5 MHz convex probe) and serum ALP measurement within 6 hours of admission. All participants then received MRCP within 48 hours, interpreted by a radiologist blinded to TAUS and ALP results. In a subset proceeding to surgery (n=80), intraoperative findings and cholangiography confirmed stone presence and clearance. We calculated sensitivity, specificity, positive and negative predictive values, overall accuracy and area under the receiver‑operating‑characteristic curve (AUC) for TAUS, ALP ≥ 400 IU/L and their combination. Results: Of 210 enrolled patients (mean age 45.7 ± 12.5 years; 61.9 % female), MRCP confirmed choledocholithiasis in 122 (58.1 %). TAUS detected stones with 78.7 % sensitivity, 72.1 % specificity, 80.0 % PPV and 71.1 % NPV. ALP ≥ 400 IU/L yielded 65.6 % sensitivity, 42.0 % specificity, 61.1 % PPV and 46.8 % NPV. Among 80 surgically explored patients, 68 (85 %) had stones confirmed and 42 of 45 (93.3 %) underwent successful intraoperative cholangiographic clearance. Conclusion: High‑resolution TAUS outperform ALP ≥ 400 IU/L for non‑invasive choledocholithiasis detection and should remain the frontline diagnostic modality. MRCP or endoscopic ultrasound should be reserved for equivocal cases or intermediate‑risk patients.