PET/CT Using FDG-Labeled Leukocytes Detects Infection in Acute Pancreatitis Patients

Acute pancreatitis (AP) is an abrupt inflammation of the pancreas. It can have severe complications and high mortality despite treatment. Whereas mild cases of AP are frequently effectively treated with conservative measures, such as nil per os (NPO) and aggressive intravenous fluid rehydration, severe cases may require admission to the intensive care unit or even surgery to deal with complications of the disease process. Early detection of infection in AP affects the choice of treatment and clinical outcome.

“Documenting infection of pancreatic necrosis/pancreatic or peripancreatic fluid collections is one of the key questions in managing such patients. So far only fine needle aspiration under radiological guidance could establish that with limitations of invasive procedure and at times insufficient amount of aspirate,” said Anish Bhattacharya, MD, Postgraduate Institute of Medical Education and Research (Chandigarh, India), and lead author of the study, which was reported in the August 2014 issue of the Journal of Nuclear Medicine.

The researchers utilized positron emission tomography/computed tomography (PET/CT) imaging using 18F-fluorodeoxyglucose (FDG)-labeled autologous leukocytes for the diagnosis of infected fluid collections in acute pancreatitis. “The present study, for the first time, gives evidence of a noninvasive investigation that can answer the question of infected pancreatic fluid collections. It even distinguishes two collections, one with and the other without infection. It could also be used to follow up with such patients after a radiological or endoscopic intervention,” added Dr. Bhattacharya.

In the study, the researchers studied 41 patients, 28 male, and 13 female, aged 21–69 with AP and radiologic evidence of fluid collection in or around the pancreas. Leukocytes were separated from the patient’s venous blood, labeled with 18F-FDG and re-injected intravenously, followed by PET/CT imaging two hours later. A final diagnosis of infection was based on microbiologic culture of fluid aspirated from the collection. Patients were treated with supportive care and antibiotics; percutaneous drainage/laparotomy was performed when indicated.

Blood glucose, total leukocyte count, neutrophil count, and leukocyte labeling efficiency varied from 83 to 212 (118 ± 30) mg/100 mL, 4,600 to 24,200 (1,1648 ± 5,376)/mm3, 55%–90% (73 ± 10) and 31%–97% (81 ± 17), respectively. Increased tracer uptake was seen in the collection in 12 out of 41 patients; 10 had culture-validated infection and underwent percutaneous drainage, while aspiration was unsuccessful in two. The scan was negative for infection in 29 patients (25 out of 29 fluid cultures negative for infection and aspiration unsuccessful in four). Sensitivity, specificity and accuracy of the scan were 100% in 35 patients in whom fluid culture reports were available.

“This research uses a new technique to diagnose infection occurring in patients with pancreatic fluid collections. The patient is spared empirical antibiotic therapy or radiological intervention followed by time-consuming microbiological work-up,” noted Dr. Bhattacharya.

The search for a suitable infection imaging radiopharmaceutical agent has continued for several decades now, noted Dr. Bhattacharya. “This study suggests that PET-CT using FDG-labeled leukocytes may be useful in swiftly and accurately detecting or ruling out active infection in any part of the body, bringing nuclear medicine to the forefront of clinical management in these situations. This would encourage researchers to identify more such techniques in future,” he said.

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