Abstract
Testing for pheochromocytoma becomes more frequent in clinical practice. False positive
test results may cause patient anxiety and unnecessary imaging studies. The data on
false positive results for pheochromocytoma in routine clinical practice are lacking.
To examine the prevalence of false positive results and to reveal the clinical features
and laboratory tests of patients with markedly elevated but false positive test results,
a database of tests for pheochromocytoma at a large general hospital between 2000
and 2008 was reviewed. Of 1 896 patients tested, 417 (22.0%) had at least one abnormal
test result and 66 (3.5%) had markedly elevated results. 24 patients with markedly
elevated but false positive results received 65 imaging studies and 1 adrenalectomy.
The causes of the misleading results included physiological variations (33%), laboratory
errors (29%), and drug interference with measurement (21%). The false positive rate
of a markedly elevated result was lowest for vanillylmandelic acid (9%) and highest
for urine metanephrines (50%) (p=0.03). Nearly half of all test results were normal and 79% of patients had at least
one normal result. Therefore false positive test results for pheochromocytoma are
rather common. Markedly elevated but false positive test results can potentially be
avoided by judicious selection of patients and tests. Pretest risk, physiological
variations of catecholamine levels, laboratory errors, and drug interference should
be considered in interpreting abnormal test results.
Key words
pheochromocytoma - laboratory tests - false positive results
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Correspondence
R. YuMD,PhD
Division of Endocrinology and Carcinoid and Neuroendocrine Tumor Center
Cedars-Sinai Medical Center
B-131
8700 Beverly Blvd
Los Angeles, CA 90048
Phone: 310-423-4774
Fax: 310-423-0440
Email: run.yu@cshs.org