, Plasma (free) analysis by LC-MS/MS Carmen L. Wiley, PhD, DABCC, FACB and Catherine P. Riley, MS

CLINICAL APPLICATION The primary measurement of and in patient plasma is ORDER CODE: clinically relevant as a screening test for the presumptive diagnosis of - secreting , adrenal medullary or other neural crest tumors. This test can also be utilized for the initial diagnosis of hypertonia. PFMETS

CLINICAL BACKGROUND Metanephrine and normetanephrine are the physiological breakdown products of , and noradrenaline. Catecholamines are biogenic which QuickQuick FFactsacts are synthesized from the amino acid via the intermediate product dopa. They are synthesized predominately in the adrenal medulla and in the nerve ends of the sympathetic nervous system, where they are stored in the granula and released to specifi c stimulus. The • Evaluation of metanephrines main role of catecholamine is to help to body adapt to acute and chronic stress. in plasma is valuable as a fi rst- line screen for suspected The diseases associated with an increased concentration of metanephrine and pheochromocytomas and other normetanephrine are catecholamine-producing tumors such as , neural crest cell derived tumors. ganglioneuroma and . Of these, phenochromocytoma has the greatest Pheochromocytomas are rare but signifi cance. Pheochromocytoma is a tumor that develops in the adrenal medulla from potentially lethal. chromaffi n cells and can produce episodes of hypertension with palpitations, severe headaches, and sweating spells. Patients with pheochromocytoma may also present with • Metanephrines are extremely sustained hypertension, an incidentally discovered adrenal mass or may be asymptomatic. stable metabolites that are An unidentifi ed phenochromocytoma poses a serious risk to the patient and although these co-secreted with catecholamines, tumors are rare they are potentially lethal. resulting in sustained elevations in the plasma making them Approximately 1000 cases ( <1:100,000) of pheochromocytoma are diagnosed in more sensitive and selective United States yearly with most occurring in young or middle age adults. However, the than catecholamines in the disease can present at an earlier age in cases where it is hereditary. Around 10% of all identifi cation of neural crest phenochromocytomas show malignant growth and can be cured by operative therapy tumors. combined with medications. • Given that the levels are low CLINICAL MANAGEMENT for metanephrine and The measurement of plasma free metanephrines is the best test for excluding normetanephrine in the pheochromocytoma. The test’s sensitivity approaches 100%, making it extremely unlikely normal population, LC-MS-MS that individuals with normal plasma metanephrine and normetanephrine levels suffer from testing is ideal. pheochromocytoma. Due to the low prevalence of pheochromocytomas and related tumors, it is recommended to confi rm elevated plasma free metanephrines with a second, different testing strategy in order to avoid false-positive test results. Normal plasma metanephrine results typically excludes a diagnosis of pheochromocytomas. The recommended second- line test is measurement of fractionated 24-hour urinary catecholamines (CATUQ: CATECHOLAMINES FRACTIONATED, URINE 24HR). In most cases, this strategy will suffi ce in confi rming or excluding the diagnosis. LAB TEST CONNECT

Metanephrines, Plasma (free) analysis by LC-MS/MS_TCL_MPFA_0003 041113 Metanephrines, Plasma (free) analysis by LC-MS/MS

TEST INFORMATION METANEPHRINES, PLASMA (FREE) ANALYSIS BY LC-MS/MS DESCRIPTION The measurement of metanephrine and normetanephrine in patient plasma is a screening test for catecholamine-secreting pheochromocytomas, adrenal medullary neoplasms or other neural crest tumors. This test can also be utilized for the initial diagnosis of hypertonia. METHOD Tandem Mass Spectrometry ORDER CODE PFMETS CPT CODES 83835 SPECIMEN Plasma, (0.5 mL minimum, 2.0 mL preferred). Collect specimen and place in an ice bath. Centrifuge within 1 hour. Transfer 2 mL REQUIREMENTS of plasma to a standard PAML aliquot tube and refrigerate immediately. Store and transport refrigerated. COMMENTS The plasma may be stored at 2-8°C for up to 7 days, or for prolonged storage kept at -20°C or below for up to 1 month. Samples left at room temperature for beyond 12 hours are unacceptable. RANGES METANEPHRINES, FREE, PLASMA Reference Range Units Metanephrine, Free 0.0 - 0.49 nmol/L Normetanephrine, Free 0.0 - 0.89 nmol/L Total, Free (MN + NMN) 0.0 - 1.38 nmol/L

This test is useful in the detection of pheochromocytoma. Most patients who present with this condition have a plasma metanephrine and/or normetanephrine concentration greater than 10 times the upper limit of normal.

Patients with moderate elevations of metanephrine and/or normetanephrine (up to 4 times the upper limit of the normal range) may be due to medication or stress. If clinical suspicion remains, repeat plasma testing or test for metanephrines in a 24 hour urine collection.

To Convert units to pg/mL multiply the MN result by 182.2 and NMN by 197.0 Ref Range: MN = < 25 pg/mL NMN = < 175 pg/mL TEST SCHEDULE Mon, Wed, Fri TURNAROUND TIME 2 - 5 days

SELECTED REFERENCES

1. Schimnich A, Preissner CM, Young WF Jr, et al. Plasma or urine fractionated metanephrines follow-up testing improves the diagnostic accuracy of plasma fractionated metanephrines for pheochromocytoma. J Clin Endocrinol Metab. 2008;93:91-95.

2. Clarke MW, Cooke B, Hoad K, Glendenning P. Improved plasma free metadrenaline analysis requires mixed mode cation exchange solid-phase extraction prior to liquid chromatography tandem mass spectrometry detection. Ann Clin Biochem. 2011 Jul;48(Pt 4):352-7.

3. Marney LC, Laha TJ, Baird GS, Rainey PM, Hoofnagle AN. Isopropanol protein precipitation for the analysis of plasma free metanephrines by liquid chromatography-tandem mass spectrometry. Clin Chem. 2008 Oct; 54(10):1729-32.