The challenge of improving the diagnostic yield from metanephrine testing in suspected phaeochromocytoma and paraganglioma

Background

Plasma-free metanephrines (PFM) or urinary fractionated metanephrines (UFM) are the preferred biochemical tests for the diagnosis of phaeochromocytoma and paraganglioma (PPGL). Borderline increased results should be followed up to either exclude or confirm diagnosis.

Methods

We extracted all PFM and UFM results reported by our laboratory over a six-month period from the laboratory information system. We categorized patients with borderline increased results according to whether follow-up testing had been performed as suggested in the initial laboratory report. Questionnaires were then sent to all requesting doctors and medical notes reviewed where available.

Results

Two hundred and four patients with borderline increased PFM or UFM were identified. Sixty-five (38.5%) of 169 patients with borderline increased PFM had a repeat test out of which 36 were normal and 29 did not normalize. Of 35 patients with borderline increased UFM, 17 (48.6%) had subsequent PFM measurement, out of which 15 were normal. Questionnaires were returned to 106 (52%) patients. Of these, the most frequent indication for testing was hypertension ( n = 50); 15 patients had an incidental adrenal mass and two of these patients were diagnosed with a phaeochromocytoma.

Conclusion

Only 38% of patients with borderline increased PFM had a repeat PFM measurement. This was not significantly higher when compared with the 28% in a previous audit that we reported in 2010 ( P = 0.10). Forty-nine per cent of patients with a borderline increased UFM had a repeat UFM or PFM measurement. There remains a substantial possibility of missed detection of PPGL.

Relationship between Vitamin D Status and Autonomic Nervous System Activity

Vitamin D deficiency is associated with increased arterial stiffness. However, the mechanisms underlying this association have not been clarified. The aim was to investigate whether changes in autonomic nervous system activity could underlie an association between 25 hydroxy vitamin D and arterial stiffness. A total of 49 subjects (age = 60 ± 8 years, body mass index = 26.7 ± 4.6 kg/m², 25 hydroxy vitamin D = 69 ± 22 nmol/L) underwent measurements of pulse wave velocity (PWV) and augmentation index (AIx), spontaneous baroreflex sensitivity, plasma metanephrines and 25 hydroxy vitamin D. Subjects with 25 hydroxy vitamin D ≤ 50 nmol/L were restudied after 200,000 International Units 25 hydroxy vitamin D. Plasma metanephrine was positively associated with AIx (p = 0.02) independent of age, sex, smoking and cholesterol and negatively associated with 25 hydroxy vitamin D (p = 0.002) independent of age, sex and season. In contrast, there was no association between baroreflex sensitivity and 25 hydroxy vitamin D (p = 0.54). Treatment with vitamin D increased 25 hydroxy vitamin D from 43 ± 5 to 96 ± 24 nmol/L (p < 0.0001) but there was no significant change in plasma metanephrine (115 ± 25 vs. 99 ± 39 pmol/L, p = 0.12). We conclude that as plasma metanephrine was negatively associated with 25 hydroxy vitamin D and positively with AIx, it could mediate an association between these two variables. This hypothesis should be tested in larger interventional studies.

A simple and rapid analytical method based on solid-phase extraction and liquid chromatography-tandem mass spectrometry for the simultaneous determination of free catecholamines and metanephrines in urine and its application to routine clinical analysis

OBJECTIVES

Urinary catecholamines and metanephrines are biochemical indicators of pheochromocytoma. We developed and validated a rapid and precise analytical method based on solid-phase extraction (SPE) and liquid chromatography separation coupled to tandem mass spectrometry (LC-MS/MS) for measuring urinary free catecholamines and metanephrines in a clinical setting.

METHODS

Following SPE purification of catecholamines and metanephrines from urine specimens, chromatographic separation and quantitative detection were performed using LC-MS/MS. The developed method for simultaneous measurement of urinary free catecholamines and metanephrines was validated with clinical urine specimens and was compared with other clinical and biochemical results, including urinary total metanephrines, vanillylmandelic acid (VMA), and plasma free metanephrines.

RESULTS

The performance of our newly developed method for measuring urinary free epinephrine (EPI), norepinephrine (NE), dopamine (DA), metanephrine (MN), and normetanephrine (NMN), was acceptable. The recoveries and matrix effects of analytes were 61-107% and 84.5-130.7%. The linear ranges of each analyte were 3.8-2163μg/L, 7.4-2,359μg/L, 5.4-2,825μg/L, 3.5-2,466μg/L, and 3.7-2,569μg/L, and the coefficients of variation (CV) were less than 10% with respect to imprecision. Carryover and sample stability were also validated. Validation using clinical urine specimens by comparison with various biochemical results showed that urinary free metanephrines had comparable sensitivity (100%) and superior specificity (97.1%) to urinary total and plasma free metanephrines.

CONCLUSIONS

The facile and reliable simultaneous measurement method for urinary free catecholamines and metanephrines using LC-MS/MS developed in this study is helpful in obtaining information about multiple metabolites and is applicable to routine clinical settings for the screening of pheochromocytoma.

Multiple Reaction Monitoring with Multistage Fragmentation (MRM3) Detection Enhances Selectivity for LC-MS/MS Analysis of Plasma Free Metanephrines

BACKGROUND

LC-MS/MS with multiple reaction monitoring (MRM) is a powerful tool for quantifying target analytes in complex matrices. However, the technique lacks selectivity when plasma free metanephrines are measured. We propose the use of multistage fragmentation (MRM3) to improve the analytical selectivity of plasma free metanephrine measurement.

METHODS

Metanephrines were extracted from plasma with weak cation exchange solid-phase extraction before separation by hydrophilic interaction liquid chromatography. We quantified normetanephrine and metanephrine by either MRM or MRM3 transitions m/z 166→134→79 and m/z 180→149→121, respectively.

RESULTS

Over a 6-month period, approximately 1% (n = 21) of patient samples showed uncharacterized coeluting substances that interfered with the routine assay, resulting in an inability to report results. Quantification with MRM3 removed these interferences and enabled measurement of the target compounds. For patient samples unaffected by interferences, Deming regression analysis demonstrated a correlation between MRM3 and MRM methods of y = 1.00x − 0.00 nmol/L for normetanephrine and y = 0.99x + 0.03 nmol/L for metanephrine. Between the MRM3 method and the median of all LC-MS/MS laboratories enrolled in a quality assurance program, the correlations were y = 0.97x + 0.03 nmol/L for normetanephrine and y = 1.03x − 0.04 nmol/L for metanephrine. Imprecision for the MRM3 method was 6.2%–7.0% for normetanephrine and 6.1%–9.9% for metanephrine (n = 10). The lower limits of quantification for the MRM3 method were 0.20 nmol/L for normetanephrine and 0.16 nmol/L for metanephrine.

CONCLUSIONS

The use of MRM3 technology improves the analytical selectivity of plasma free metanephrine quantification by LC-MS/MS while demonstrating sufficient analytical sensitivity and imprecision.

Analysis of plasma 3-methoxytyramine, normetanephrine and metanephrine by ultraperformance liquid chromatography-tandem mass spectrometry: utility for diagnosis of dopamine-producing metastatic phaeochromocytoma

BACKGROUND

Measurements of plasma normetanephrine (NMN) and metanephrine (MN) provide a sensitive test for diagnosis of phaeochromocytomas and paragangliomas (PPGLs), but do not allow detection of dopamine-producing tumours. Here we introduce a novel mass spectrometric based method coupled to ultraperformance liquid chromatography (LC-MS/MS) for measuring NMN, MN and 3-methoxytyramine (MTY), the O-methylated metabolite of dopamine.

METHODS

Specific collision-induced fragment ions assessed by multireaction monitoring transitions were used for identification, with quantification according to signal intensities of analytes relative to stable isotope labelled internal standards. Results for solid-phase extracted samples from 196 subjects analysed by LC-MS/MS were compared with those analysed by liquid chromatography with electrochemical detection (LC-ECD). Concentration ranges in 125 volunteers were compared with those from 63 patients with PPGLs, including 14 with metastatic disease.

RESULTS

The LC-MS/MS method showed linearity over four orders of magnitude with analytical sensitivity sufficient to measure to 0.02 nmol/L. Intra- and inter-assay coefficients of variation ranged from 2.8% to 13.5%. NMN and MN were respectively measured 17% and 10% higher and MTY 26% lower by LC-MS/MS than by LC-ECD. Medians and ranges for 3-methoxytramine, NMN and MN were respectively 0.08 (0.03-0.13), 0.35 (0.13-0.95) and 0.15 (0.07-0.33) nmol/L in volunteers. Among patients with PPGLs, plasma methoxytyramine was six-fold higher in patients with than without metastastases (1.09 versus 0.19 nmol/L) and in three patients was the only metabolite increased.

CONCLUSIONS

The LC-MS/MS method enables accurate, selective and sensitive measurements of catecholamine O-methylated metabolites that should be particularly useful for screening and management of dopamine-producing metastatic PPGLs.