Plasma chromogranin A or urine fractionated metanephrines follow-up testing improves the diagnostic accuracy of plasma fractionated metanephrines for pheochromocytoma.
BACKGROUND
The initial diagnosis of pheochromocytoma relies on plasma fractionated metanephrines levels. Normal levels exclude pheochromocytoma, but positive tests have a low positive predictive value due to the disease's rarity.


OBJECTIVE
The objective of the study was to evaluate three approaches to distinguish between true-positive and false-positive tests: 1) increased cutoff for plasma fractionated metanephrines, 2) measurement of serum/plasma chromogranin A (CGA), and 3) urine fractionated metanephrine testing.


METHODS
We studied retrospectively all Mayo Clinic patients with positive plasma fractionated metanephrine tests over a 15-month period and determined their final diagnosis based on histology, imaging, additional biochemical tests, and more than 1 yr follow-up. For a subgroup, urine fractionated metanephrine results were available. All original plasma samples were retested for CGA.


RESULTS
Of 140 patients, 40 had a chromaffin tumor confirmed and 100 excluded, indicating a positive predictive value of plasma fractionated metanephrines of 28.6%. Increasing the threshold for a positive test improved specificity to 98% but missed eight cases (20%). Incorporation of urine fractionated metanephrine testing as follow-up test achieved 80% specificity and 91% sensitivity. The corresponding figures for CGA were 71 and 87% for all patients and 89 and 87% when patients taking proton pump inhibitors were excluded.


CONCLUSIONS
Unless plasma fractionated metanephrines levels are elevated more than 4-fold above the upper limit of normal, patients with a positive plasma fractionated metanephrines test should be evaluated with urine fractionated metanephrines and serum/plasma CGA assays before being subjected to imaging or invasive diagnostic tests.
Algeciras-Schimnich
Alicia
A
Department of Laboratory Medicine and Pathology, Mayo Clinic, 200 First Street Southwest, Rochester, Minnesota 55905, USA.
Preissner
Carol M
CM
Young
William F
WF
Singh
Ravinder J
RJ
Grebe
Stefan K G
SK
D000310:Adrenal Gland Neoplasms / Q000097:blood* / Q000652:urine*; D053379:Chromogranin A / Q000097:blood*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008676:Metanephrine / Q000097:blood* / Q000652:urine*; D008875:Middle Aged; D008910:Minnesota; D010673:Pheochromocytoma / Q000097:blood* / Q000652:urine*; D011237:Predictive Value of Tests; D012372:ROC Curve; D012189:Retrospective Studies
D053379:Chromogranin A; D008676:Metanephrine