How to Diagnose Pheochromocytoma: Labs, Imaging & Genes

Pheochromocytoma diagnosis follows a three-step sequence: biochemical confirmation through blood or urine tests for catecholamine metabolites, anatomical imaging to locate the tumor, and genetic testing to identify hereditary causes. The single most important first step is measuring plasma free metanephrines, a blood test with sensitivity around 96 to 99 percent that catches nearly every tumor. But what seems like a straightforward lab-then-scan pathway gets complicated quickly by false positives, medication interference, tumors that produce no symptoms, and a surprisingly high rate of inherited mutations that demand lifelong surveillance.

Who Should Be Tested in the First Place

Not everyone with high blood pressure needs a pheochromocytoma workup. The tumor is rare, affecting only a few people per million each year, and screening the general hypertension population would generate far more false alarms than real diagnoses. Current recommendations target testing toward people whose clinical picture raises the odds enough to justify it: those with blood pressure that spikes in sudden episodes, resists standard treatment, or appeared unusually early in life; people with symptoms suggesting bursts of adrenaline-like activity such as pounding headaches, rapid heart rate, and drenching sweats; patients with hereditary syndromes known to carry pheochromocytoma risk; and anyone with an adrenal mass discovered incidentally on imaging that measures above 10 Hounsfield units on a non-contrast CT scan.

That last group, the incidentalomas, has become the most common route to diagnosis. In one study of 92 confirmed cases, roughly two-thirds were discovered by accident during imaging done for something else entirely. The classic triad of headache, sweating, and palpitations was present in only about 14 percent of those incidental cases, and a full 12 percent had no symptoms at all.² A recent case report underscored the point: a woman in her late seventies had a 5-centimeter adrenal mass found during unrelated imaging, with well-controlled blood pressure and zero classic symptoms, yet her biochemical testing confirmed pheochromocytoma.³ The takeaway is that waiting for textbook symptoms means missing the majority of tumors.

The First-Line Blood Test

The diagnostic workhorse is the measurement of plasma free metanephrines, which are breakdown products of the hormones norepinephrine and epinephrine. What makes these metabolites so useful is that pheochromocytoma cells continuously convert catecholamines into metanephrines inside the tumor itself, regardless of whether the tumor is actively releasing hormones into the bloodstream. That means plasma free metanephrines stay elevated even between symptomatic episodes, avoiding the false negatives that plagued older tests relying on catching a spike of catecholamines at the right moment.⁴

In a landmark study comparing six different biochemical tests, plasma free metanephrines had a sensitivity of 99 percent, meaning they missed virtually no tumors. That sensitivity was higher than urinary catecholamines at 86 percent, plasma catecholamines at 84 percent, and urinary vanillylmandelic acid (VMA) at just 64 percent. When both sensitivity and specificity were compared using diagnostic accuracy curves, plasma free metanephrines came out on top overall.⁵ Urinary fractionated metanephrines, collected over 24 hours, run close in sensitivity but have lower specificity, meaning more false positives. One study directly comparing the two approaches found matched sensitivities of about 96 percent, but urinary specificity was significantly better than plasma drawn while sitting, at roughly 94 percent versus 76 percent.⁶

This gap in specificity matters in practice. Blood drawn while a patient is sitting tends to yield more borderline elevations than blood drawn after resting supine for 20 to 30 minutes. Many clinics draw samples from seated patients for convenience, but the tradeoff is a higher false-positive rate and more follow-up testing. If the initial screen comes back mildly elevated, repeating the test after supine rest or switching to a 24-hour urine collection can help sort real disease from a physiological blip.

Medications That Muddy the Results

Certain drugs can push metanephrine levels above the normal range even when no tumor is present, and norepinephrine reuptake blockers are the biggest culprits. These include some antidepressants, particularly tricyclics and serotonin-norepinephrine reuptake inhibitors. In one study, patients taking norepinephrine reuptake blockers had plasma normetanephrine levels about 40 percent higher on average than people not on those drugs, and the false-positive rate jumped from under 5 percent to 23 percent. Tricyclic antidepressants drove another metabolite, methoxytyramine, up by 127 percent, with a false-positive rate ballooning from under 1 percent to nearly 29 percent.⁷ Most of these elevations are mild, but there are exceptions: one highlighted case showed levels more than six times the upper limit of normal purely from medication, initially mimicking a pheochromocytoma convincingly until functional imaging ruled it out and levels normalized after stopping the drug.

A separate multivariable analysis confirmed that norepinephrine reuptake blockers were the only drug class independently linked to raised normetanephrine, and the effect was dose-dependent. Antipsychotics and nicotine use also influenced methoxytyramine levels. Importantly, selective serotonin reuptake inhibitors (SSRIs) did not raise any of these metabolites.⁸ When a patient on one of these medications has borderline metanephrine levels, clinicians face a judgment call: withdraw the medication for a retest (which requires psychiatric clearance and careful management), proceed to imaging, or use a confirmatory test like the clonidine suppression test.

Sorting Borderline Results With the Clonidine Suppression Test

When plasma metanephrines are elevated but not dramatically so, the clonidine suppression test can help distinguish a true tumor from a false alarm. Clonidine lowers the nervous system’s release of norepinephrine but does not affect tumor-produced catecholamines. A patient takes a dose of clonidine, and blood is redrawn a few hours later. If normetanephrine fails to drop adequately, the suspicion for pheochromocytoma stays high.

This test performs well in the borderline zone. Using age-adjusted cutoffs, one study achieved a sensitivity of 94 percent and specificity of 97 percent, though two patients with small tumors slipped through.⁹ A separate analysis concluded that the clonidine suppression test correctly identified all false-positive screening results when used in the right clinical context, specifically for patients whose initial plasma normetanephrine was only modestly above normal.¹⁰ Its accuracy drops in patients with very low baseline catecholamine levels, where a stimulatory test using glucagon may be more informative.¹¹

Chromogranin A as a Supporting Marker

Chromogranin A is a protein released by neuroendocrine cells and can serve as a complementary blood marker. It is not a replacement for metanephrines but fills a specific gap: nonfunctional tumors. Some paragangliomas, particularly those in the head and neck, produce little or no catecholamine excess, which means metanephrine tests may come back normal despite an active tumor. In one series, chromogranin A was elevated in about 87 percent of confirmed pheochromocytoma and paraganglioma patients at diagnosis, with sensitivity reaching 97 percent for adrenal pheochromocytomas specifically. For nonfunctional paragangliomas, chromogranin A was elevated in about 62 percent and showed potential as a follow-up marker.¹² Sensitivity improves with tumor size: one analysis found it was about 70 percent for tumors under 5 centimeters and 95 percent for those 5 centimeters or larger.¹³ Clinicians also use it during follow-up, as rising chromogranin A levels have occasionally been the first sign of recurrence before other biochemical markers or imaging caught on.¹²

Locating the Tumor With CT and MRI

Once biochemistry confirms catecholamine excess, the next step is finding the tumor. CT of the abdomen and pelvis is the standard starting point. Most pheochromocytomas sit on one of the adrenal glands, and on non-contrast CT they typically measure above 10 Hounsfield units, helping to distinguish them from the more common benign adrenal adenomas that tend to be fat-rich and measure below that threshold. Arterial-phase CT boosts differentiation further. In one study, arterial-phase attenuation values provided excellent discriminatory power, with an area-under-the-curve of 0.967, and a cutoff of about 140 Hounsfield units offered 100 percent specificity for pheochromocytoma.¹⁴

There is, however, a well-documented pitfall. A small fraction of pheochromocytomas contain enough intracellular fat to mimic adenomas. A case series found that two of nine pheochromocytomas had attenuation values below 10 Hounsfield units on non-contrast CT and even showed rapid contrast washout, the very pattern that radiologists rely on to call a mass a benign adenoma. These low-density pheochromocytomas are rare but dangerous to miss, which is why biochemical testing should not be skipped even when a mass “looks like” an adenoma on imaging.¹⁵

MRI is a reasonable alternative, particularly in patients who cannot receive iodinated CT contrast or in whom radiation exposure is a concern, such as children and pregnant women. On T2-weighted MRI, pheochromocytomas classically appear very bright, though this “lightbulb sign” is not universal. Both CT and MRI perform similarly for identifying adrenal tumors, but neither is sufficient on its own for ruling out extra-adrenal disease or metastases, which is where functional imaging enters the picture.

Functional Imaging for Difficult and Metastatic Cases

Functional imaging uses radioactive tracers that target specific biological properties of pheochromocytoma cells. For decades, MIBG scintigraphy was the go-to: the tracer is taken up by the same transport mechanism that moves norepinephrine into tumor cells. A large prospective trial of 123-I MIBG reported sensitivity of 82 to 88 percent and specificity of 82 to 84 percent for primary or metastatic disease, with somewhat lower sensitivity for extra-adrenal tumors at 67 percent.¹⁶

MIBG has been steadily displaced by 68-Gallium DOTATATE PET/CT, which targets somatostatin receptors expressed on pheochromocytoma and paraganglioma cells. Head-to-head comparisons consistently favor the newer scan. In one study, DOTATATE PET/CT had a per-patient sensitivity of 100 percent compared to about 78 percent for MIBG.¹⁷ Another found DOTATATE’s lesion-based sensitivity for primary tumors was 94 percent versus 75 percent for MIBG, and for metastatic disease it was 85 percent versus 59 percent.¹⁸ The advantage is especially striking for metastatic disease involving bone. A study focused on spinal metastases found DOTATATE detected nearly 99 percent of lesions compared to 72 percent for FDG-PET and just 45 percent for whole-body CT.¹⁹

For tumors driven by SDHB mutations, which carry a higher risk of metastatic spread, DOTATATE PET/CT has been shown to identify about 99 percent of lesions, outperforming every other functional modality and CT/MRI.²⁰ MIBG still has a role in treatment planning, since patients whose tumors take up MIBG may be candidates for MIBG-based radionuclide therapy, but for pure diagnostic localization, DOTATATE is now the preferred scan where available.

Why Every Patient Needs Genetic Testing

Pheochromocytoma has one of the highest rates of hereditary causation of any tumor. A large universal screening study found that about 28 percent of patients with pheochromocytoma or paraganglioma carried a disease-causing germline mutation. The most commonly affected gene was SDHB, accounting for about 40 percent of positive results, followed by SDHD at 21 percent, SDHA at 10 percent, and VHL at 8 percent. Smaller shares went to SDHC, RET, MAX, and several rarer genes.²¹ A critical finding from that same study: restricting testing to just the three most obvious SDH genes (SDHB, SDHC, SDHD) would have missed about a third of patients with mutations. Broad multi-gene panels catch more.

The mutation rate is even higher in specific subgroups. Paragangliomas carry germline mutations more often than adrenal pheochromocytomas, with rates of about 29 percent versus 5 percent in one series of 329 patients.²² Patients with extra-adrenal tumors and a family history had an 86 percent chance of carrying a mutation in the larger study.²¹ Data from a smaller Japanese cohort found pathogenic variants in about 22 percent of patients, confirming that the high hereditary rate is not confined to European populations.²³

Knowing the specific gene matters for clinical management. SDHB mutations carry a higher risk of metastatic disease, particularly when tumors are larger than 5 centimeters, located outside the adrenal gland, or show elevated methoxytyramine levels.²⁴ VHL mutations predispose to other tumors such as kidney cancer and retinal lesions. RET mutations are linked to multiple endocrine neoplasia type 2, which also involves thyroid cancer. Genetic results determine the surveillance schedule, what other organs to screen, and whether family members should be tested.

Pheochromocytoma in Children

Pediatric cases deserve their own mention because the hereditary rate is dramatically higher. Up to 80 percent of pheochromocytomas in children are inherited, compared to roughly a quarter in adults.²⁵ An international consensus statement recommends genetic testing for all children with pheochromocytoma or paraganglioma, as well as for any child whose first-degree relative carries a known disease-causing variant.²⁶ Many pediatric diagnoses now come through presymptomatic screening in families already known to carry mutations for syndromes like MEN2 or von Hippel-Lindau disease.²⁷

The biochemical workup in children is essentially the same, with plasma free metanephrines preferred in those with a high pretest probability. For younger children with low clinical suspicion and needle phobia, a first-morning spot urine sample has been proposed as a less invasive alternative, though prospective validation studies are still needed.²⁶ Given the high mutation rate, lifelong surveillance for recurrence is recommended in every pediatric patient.

Pseudopheochromocytoma and When the Workup Comes Back Negative

Some patients present with the full clinical picture of pheochromocytoma — sudden severe blood pressure spikes, pounding heart, sweating, anxiety — yet their metanephrine levels are normal and no tumor appears on imaging. This condition is called pseudopheochromocytoma, and it involves severe paroxysmal hypertension without true catecholamine excess or an identifiable mass. The symptoms overlap with but are not identical to those of genuine catecholamine-secreting tumors.²⁸ Understanding that this entity exists is important because it prevents patients from undergoing unnecessary adrenal surgery or repeated rounds of imaging chasing a tumor that is not there. The causes of pseudopheochromocytoma are varied and can include panic disorder, obstructive sleep apnea, baroreflex dysfunction, and certain medications. Treatment is directed at the underlying cause rather than the adrenal gland.

Assessing Whether a Tumor May Be Aggressive

No reliable way exists to definitively call a pheochromocytoma “benign” or “malignant” at the time of initial surgery. The World Health Organization now acknowledges that all pheochromocytomas and paragangliomas carry some metastatic potential, though the risk varies enormously. Histopathological scoring systems have been developed to try to stratify risk. A comparative study of three such systems found that a modified scoring tool incorporating SDHB immunohistochemistry had the best specificity and negative predictive value, reaching about 71 percent and 98 percent respectively. In other words, it was relatively reliable at ruling out aggressive behavior, though its sensitivity for catching all aggressive tumors was low at about 21 percent.²⁹ Expert consensus for SDHB-mutated tumors identifies initial tumor size above 5 centimeters, extra-adrenal location, and elevated plasma methoxytyramine as features associated with higher progression and metastasis rates.²⁴ Because no single test definitively predicts behavior, long-term follow-up with periodic biochemical and imaging surveillance remains the standard approach for everyone diagnosed with these tumors.

Pregnancy and Pheochromocytoma

Diagnosing pheochromocytoma during pregnancy is rare but carries high stakes: an unrecognized tumor during labor can trigger a hypertensive crisis dangerous for both mother and baby. The symptoms — high blood pressure, headaches, sweating — overlap with preeclampsia, making the diagnosis easy to miss. Biochemical confirmation follows the same principle as in non-pregnant patients, relying on plasma and urinary catecholamines and their metabolites.³⁰ The key difference is imaging: MRI without gadolinium contrast is the preferred localization method, since CT involves ionizing radiation and iodinated contrast. Functional nuclear scans are avoided during pregnancy. When a pheochromocytoma is confirmed, alpha-adrenergic blockade is started promptly, and the timing and mode of delivery are carefully planned with a multidisciplinary team.

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