Cholecystokinin cholescintigraphy: victim of its own success?

Numerous publications have reported that a low gallbladder ejection fraction (GBEF) determined by cholecystokinin (CCK) cholescintigraphy has a high positive predictive value for the diagnosis of chronic acalculous cholecystitis (CAC). Clinicians and surgeons have found this test to be clinically useful as an objective method to confirm their clinical diagnosis. However, an abnormally low GBEF is not specific for CAC. For example, numerous other diseases have been associated with a low GBEF, and various therapeutic drugs can cause poor gallbladder contraction. Importantly, improper CCK infusion methodology can result in an erroneously low GBEF. More than one third of healthy subjects and patients who receive sincalide, 0.02 microg/kg infused over 1-3 min, will have an erroneously low GBEF but will have a normal GBEF with a slower infusion (30-60 min) of the same total dose. Because of enthusiastic acceptance of CCK cholescintigraphy by clinicians, the types of patients referred for this test have changed over time. Patients investigated in publications confirming the usefulness of CCK cholescintigraphy had a high pretest likelihood of disease. They underwent extensive workup to rule out other diseases and were followed up for months or years before CCK cholescintigraphy was performed, allowing other diseases to become manifest or symptoms to resolve. However, CCK cholescintigraphy is now being used by clinicians to shorten the workup and follow-up time based on the rationale that CCK cholescintigraphy can quickly confirm or exclude the diagnosis. This new group of referral patients has a lower likelihood of the disease. Many will ultimately be diagnosed with diseases other than CAC. The positive predictive value of this test will likely be lower and the false-positive rate will likely be higher. Nuclear medicine physicians must work to minimize false-positive studies to maintain the confidence of referring clinicians. First, we can educate referring physicians as to the proper use of this study. Next, we must perform CCK cholescintigraphy using optimal methodology that will result in the lowest possible false-positive rate. And finally, we must interpret CCK cholescintigraphy in light of the patient's history, prior workup and clinical setting.