From the Research
The optimal range for metanephrines in females is typically less than or equal to 148 pg/mL for plasma free metanephrine, as marked elevations above this level are highly suggestive of pheochromocytoma or paraganglioma 1.
Key Considerations
- Metanephrines are metabolites of catecholamines and are used to diagnose conditions like pheochromocytoma and paraganglioma.
- The measurement of metanephrines can be influenced by various factors, including stress, exercise, certain medications, and substances like caffeine and alcohol.
- For accurate results, blood collection should ideally occur after the patient has been resting supine for at least 30 minutes, and patients should fast for 8-10 hours before the test.
Diagnostic Approach
- Values above the reference range do not automatically indicate disease but warrant further investigation, especially if accompanied by symptoms like episodic hypertension, headaches, sweating, and palpitations.
- The use of urinary fractionated metanephrines has been recommended for the diagnosis of pheochromocytoma, with different diagnostic cut-off values potentially needed according to sex 2.
- Recent studies have also explored the stability and reference intervals of spot urinary fractionated metanephrines and methoxytyramine by tandem mass spectrometry as a screening method for pheochromocytoma and paraganglioma, highlighting the importance of gender-specific reference intervals 3.
Clinical Implications
- The incidence of pheochromocytoma is extremely low, and clear guidelines for the referral of patients for biochemical testing are needed to avoid unnecessary costs and to identify the correct diagnosis promptly 4.
- Analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) is recommended for the measurement of metanephrines due to its high sensitivity, specificity, and throughput 5.