Evaluation of the Clonidine Suppression Test: The Cleveland Clinic Experience

The clonidine suppression test (CST) diagnoses pheochromocytoma (PCC) or paraganglioma (PGL) when initial catecholamine testing is indeterminate. Home blood pressure (BP) medications are held for 24 hours and a 0.3 mg dose of clonidine is administered orally. Given the risk of hypotension, BP is monitored every 30 minutes for 3 hours. Catecholamine levels are drawn at baseline and 3 hours. We aim to review 5 years of experience with CST at our institution with regards to adverse events and overall test performance. We report the number of PCCs and PGLs diagnosed by CST relative to the total number of PCCs and PGLs confirmed by surgical pathology at our institution in the same time frame.

Methods:

This is a retrospective cohort study of patients who had a CST at our institution between July 2016 and January 2022. We chart-reviewed patients who had CST for adverse events, CST results, and any subsequent PCC/PGL workup. Descriptive statistics were used.

Results:

From July 2016 to January 2022, there were 65 patients who had clonidine suppression testing at our institution; 43 (66%) were female with a mean age of 57 years (±12 yrs). A total of 15 patients (23%) had hypotension prompting intervention, 11 (17%) required IV fluid resuscitation. One patient required ICU admission for persistent hypotension. Other adverse effects included shortness of breath requiring supplemental oxygen in 1 patient. Regarding CST results, 7 (11%) were positive, 55 (85%) were negative, and 3 (5%) did not result due to post-collection lab errors. Of the 7 that tested positive, 1 patient went to surgery and had a pathology-confirmed PCC, 3 patients have ongoing workup, and 3 had subsequent imaging that excluded PCC/PGL. There have been no cases of PCC/PGL detected amongst patients who tested negatively on CST. Excluding pending workups, the CST sensitivity is 100% and specificity is 95%, with positive predictive value (PPV) 25% and negative predictive value (NPV) 100% in our patient population. In the same timeframe there have been 185 pathology-confirmed catecholamine-secreting tumors (81 PCCs and 104 PGLs) at our institution, 184 of which were identified by alternative diagnostic workup.

Discussion/Conclusion:

Despite the high incidence of PCC/PGL at our institution over the past 5 years, the CST has poor PPV and only a very small number of PCC/PGL cases (n=1) have been identified by this test. CST remains a good tool for ruling out PCC/PGL, but incurs resources and costs, not least of which is hypotension which occurred in nearly a quarter of our patients. Given newer imaging modalities that have diagnostic criteria for identifying pheochromocytoma, providers may wish to consider other diagnostic workup prior to CST.