How to detect pheochromocytomas?--the diagnostic relevance of plasma free metanephrines

Pheochromocytomas are chromaffin cell tumors, mostly originating from the adrenal medulla, and represent a rare cause of hypertensiondue to excessive production of catecholamines (norepinephrine and/or epinephrine). More than 10% occur in families with multiple endocrine neoplasia type II, von Hippel-Lindau disease, neurofibromatosis type I, and familial carotid body tumors. Since approximately half of the afflicted patients present without or with only episodic hypertension, detailed clinical evaluation and sensitive biochemical tests are mandatory for the diagnosis, which relies on the detection of increased catecholamine production. Commonly employed tests such as the measurement of free catecholamines in plasma and urine or of their metabolites, vanillylmandelic acid and total metanephrines (= free + conjugated normetanephrine and metanephrine) in urine, suffer from interference from external factors and sometimes low clinical sensitivity and/or specificity. Recent technical advances now allow us to measure plasma free (unconjugated) metanephrines, thus increasing clinical sensitivity and specificity to close to 100%. Plasma free metanephrines offer the following advantages for the detection of pheochromocytomas: (i) independence of short-term changes in catecholamine secretion which may result from change of posture, exercise or intraoperative stress, (ii) information on long-term increase of catecholamine production, (iii) tight correlation with tumor mass, and (iv) only minor interference from drugs. This method does not need time-consuming standardized procedures for blood sampling, which are a prerequisite for the determination of free catecholamines. In conclusion, it is therefore recommended to use plasma free metanephrines--after meticulous clinical screening--as the first-line biochemical test for detecting pheochromocytomas.     

Disappearance rate of catecholamines, total metanephrines, and neuropeptide Y from the plasma of patients after resection of pheochromocytoma

BACKGROUND: Plasma free metanephrines are a more reliable analyte to measure than catecholamines for the biochemical diagnosis of pheochromocytomas. We hypothesized that the long persistence of total (sulfate-conjugated plus free) metanephrines in the blood might have a significant diagnostic value. METHODS: We measured plasma concentrations of catecholamines and total metanephrines (sulfate-conjugated plus free forms) by HPLC with amperometric detection, and neuropeptide Y (NPY) by an amplified ELISA in seven patients before and after removal of their pheochromocytomas. The results for catecholamine, total metanephrines, and NPY in each patient were analyzed for up to 120 min, starting from the time of tumor vessel clamping. The persistence of analytes was quantified as the area under the concentration-time curve over 120 min. RESULTS: On the basis of the upper reference limit for each variable, plasma free norepinephrine (NE) and epinephrine (E) concentrations were increased preoperatively in at least one sample in seven and six patients, respectively. Total normetanephrine (NMN) and metanephrine (MN) were increased in all samples in seven and six patients, respectively. NPY was increased 2- to 465-fold. After removal of the tumor, MN and NMN showed a higher average relative increase above the upper limit of the reference interval than NE and E (P = 0.05), whereas NPY was intermediate. The persistence of increased values was significantly shorter for catecholamines than for metanephrines. The half-life estimated by nonlinear regression was 12.3 +/- 7.8 min for NPY. Significant correlations were observed among NE, E, NMN, MN, and NPY concentrations, but parent markers (E and MN or NE and NMN) did not appear significantly intercorrelated. CONCLUSIONS: A larger increase and a longer persistence of total metanephrines (reflecting predominantly sulfo-conjugated metanephrines) than catecholamines and NPY in plasma may contribute to their greater diagnostic accuracy in pheochromocytoma.     

Measurement of urinary metanephrines to screen for pheochromocytoma in an unselected hospital referral population

BACKGROUND: Despite the rarity of pheochromocytoma, diagnosis is important because of the dangers of uncontrolled severe hypertension and the availability of very effective surgical treatment. Urinary or plasma catecholamines or catecholamine derivatives are commonly used to screen for pheochromocytomas before imaging, but data from 24-h urinary metanephrine results, patient age, and sex may better predict tumors in populations with a low pretest probability. METHODS: We retrospectively studied outcomes of an unselected population (1819 patients) referred to a tertiary hospital laboratory for urinary metanephrine testing and investigated the usefulness of some simple derivative measures for detecting pheochromocytoma. We normalized values for urinary 24-h excretion of metanephrine, normetanephrine, and 3-methoxytyramine by dividing by an age- and sex-specific reference range. We then compared pheochromocytoma prediction by the use of products of these normalized measures with the gold standard of biopsy-confirmed tumor. RESULTS: The product of the excretion of normalized metanephrine (nMAD) and normalized normetanephrine (nNMT) (nMAD.nNMT) was a highly sensitive (100%) and specific (99.1%) measure, yielding a positive predictive value of 82%. ROC curves were not improved by including the normalized 3-methoxytyramine concentrations in the product. The test for nMAD.nNMT gave higher sensitivity and specificity than the tests for either substance alone. CONCLUSION: The test for nMAD.nNMT is a useful measure for identifying pheochromocytoma in a population with a low pretest probability.     

Increased catecholamine excretion after labetalol therapy: a spurious effect of drug metabolites

Patients with essential hypertension were treated for four weeks with the alpha- and beta-adreno-receptor blocking agent labetalol. Urinary excretion of total catecholamines, metanephrine plus normetanephrine and vanillylmandelic acid was measured with various methods before and during treatment. An unidentified substance interfering with the fluorimetric method for catecholamines and the photometric assay for metanephrines caused falsely high values of those substances. Using appropriate methodology no changes of total catecholamines, metanephrine plus normetanephrine and vanillylmandelic acid excretion were found after labetalol therapy. Our findings are important in preventing errors in the diagnosis of pheochromocytoma as well as in the evaluation of the effects of labetalol on the sympathetic nervous system in man.     

Radioimmunoassay of metanephrine and normetanephrine for diagnosis of pheochromocytoma

Sensitive and specific radioimmunoassays of metanephrine and normetanephrine were developed by use of 125I-labeled synephrine and specific metanephrine antibody, and 125I-labeled octopamine and specific normetanephrine antibody. Specific antibody for both metanephrine and normetanephrine was raised in rabbits by immunization with bovine serum albumin conjugated with the corresponding hapten, prepared by the method of Grota and Brown (Endocrinology 1976;98:615). The detection limits of the metanephrine and the normetanephrine radioimmunoassays were 2 and 6 pg/tube, respectively. Mean plasma metanephrine and normetanephrine values for 24 normal subjects were 62 (SD 14) and 100 (SD 40) ng/L, respectively. Mean urinary metanephrine and normetanephrine values for 22 normal subjects were 154 (SD 74) and 217 (SD 109) micrograms/day. For 14 pheochromocytoma patients, plasma metanephrine and normetanephrine values ranged from 29 to 683 and from 28 to 7850 ng/L, and urinary metanephrine and normetanephrine values were 606 to 6630 and 296 to 4800 micrograms/day, respectively. The present methods are simple and suitable for routine tests or for mass screening for pheochromocytoma.     

Freedom from drug interference in new immunoassays for urinary catecholamines and metanephrines

BACKGROUND: Determination of urinary free catecholamine and total (i. e., free plus conjugated) metanephrine excretion is considered the most clinically sensitive biochemical test for pheochromocytoma. In this study, we evaluated new immunoassay methods for the measurement of these analytes for potential drug-based interference. METHODS: Urine samples collected from patients on a variety of medications were grouped by specific drug type. The significance of any difference in the free catecholamine or total metanephrine concentrations in the different groups was assessed by one-way ANOVA. A group of patients receiving no medication was included as a control (no analytical interference). Additionally, analytical accuracy, detection limit, and precision were determined. RESULTS: No significant differences were found in the concentrations of free catecholamines or total metanephrines in urine from patients taking the medications investigated and the control group: P = 0.649 (fE), 0.221 (fNE), 0.149 (tM), and 0.170 (tNM). For free catecholamines, intraassay CVs were 4.6-18%; interassay CVs were 10-25%. For total metanephrines, intraassay CVs were 9.6-27%; interassay CVs were 5. 8-22%. Detection limits were 0.009 and 0.027 micromol/L for fE and fNE and 0.119 and 0.346 micromol/L for tM and tNM, respectively. CONCLUSIONS: None of the drugs examined in this study interfered in the measurement of free catecholamines or total metanephrines by these immunoassays. The technique is easier to use, requires less equipment, and is more accessible than HPLC. In combination, these assays are suitable as initial screening tests for pheochromocytoma.     

Adrenal and extra-adrenal pheochromocytomas: an ultrastructural and formaldehyde-induced fluorescence study with catecholamine content

Twenty-one adrenal and 6 extra-adrenal pheochromocytomas were studied by light and electron microscopy, and formaldehyde-induced fluorescence (FIF). These morphological findings were compared to the content of tumor catecholamines. Based on predominancy of the cell types, pheochromocytomas were classified into three groups: basophilic, chromophobic and oxyphilic (oncocytic) types. The basophilic type was characterized by basophilic cytoplasm of the tumor cells with hematoxylin and eosin (H & E) stain, green cytoplasmic fluorescence with FIF and numerous epinephrine type of electron dense granules with electron microscopy. Its epinephrine content was compatible to the normal adrenal medulla. The basophilic type was only of adrenal origin. Chromophobic and oxyphilic tumors contained predominantly norepinephrine, and showed yellow-green or light brown cytoplasmic fluorescence by FIF. By electron microscopy, various granules of different sizes and shapes of the norepinephrine type were noted. Extra-adrenal pheochromocytoma cells demonstrated dark brown cytoplasmic fluorescence by FIF. Morphological findings of the extra-adrenal tumor corresponded to those of chromophobic type adrenal pheochromocytoma. The tumors contained only norepinephrine.     

Urinary metanephrine radioimmunoassay: comparison with the colorimetric assay

A radioimmunoassay involving an 125I ligand has been developed and applied to the measurement of urinary metanephrine. To validate the clinical usefulness of this assay, we compared measurement of metanephrine by radioimmunoassay and of total urinary metanephrines by the Pisano colorimetric method. The radioimmunoassay is specific for metanephrine, whereas the colorimetric method measures both metanephrine and normetanephrine. We used both methods to determine urinary metanephrine or total metanephrines in subjects with essential hypertension, pheochromocytoma, the syndrome of multiple endocrine adenomatosis type 2, and normotensive volunteers. The mean and upper limit of normal (3 SD) for metanephrine by radioimmunoassay in our normotensive volunteers was 94.2 microgram/24 h and 229 microgram/24 h, respectively, which compares well with reported values of 87.6 microgram/24 h and 319 microgram/24 h by non-radioimmunoassay methods. Both radioimmunoassay and colorimetry accurately identified five patients with known pheochromocytoma. Good correlation (r = 0.993) was demonstrated between the two assays in a comparison of patients with essential hypertension and pheochromocytoma. We conclude that the radioimmunoassay is at least equivalent to the colorimetric methods in distinguishing pathological and normal catecholamine secretion, and is faster, more precise, and 1000-fold more sensitive.     

Pheochromocytoma in a patient with end-stage renal disease

Pheochromocytoma is a rare tumor. To our knowledge only 15 cases have been reported in patients with end-stage renal disease (ESRD). We describe a 46-year-old woman with ESRD and a history of paroxysmal and difficult-to-control hypertension. During anesthesia for a surgical procedure, the patient experienced blood pressure lability with systolic blood pressures ranging from 76 to 360 mm Hg. Serum catecholamine concentrations were 2,698 pg/ mL (reference value, <750 pg/mL) for norepinephrine, 33 pg/mL (<110 pg/mL) for epinephrine, and 55 pg/mL (<30 pg/mL) for dopamine. The concentrations of plasma metanephrines were 6.84 nmol/L (<0.50 nmol/L) for metanephrine and 14.64 nmol/L (<0.90 nmol/L) for normetanephrine. Abdominal computed tomography showed a right-sided, 4-cm mass posterior to the infrahepatic inferior vena cava. Following blood pressure control with alpha- and beta-adrenergic blockade, the mass was removed. Pathologic examination demonstrated the mass was a pheochromocytoma. The maximum postoperative systolic blood pressure was 160 mm Hg. Postoperative plasma normetanephrine concentration was 2.80 nmol/L, and metanephrine was obscured by interfering substances. This case report and literature review emphasizes the difficulty in diagnosing pheochromocytomas in patients with ESRD despite the myriad of available diagnostic tests.     

酶联免疫法检测间甲肾上腺素类物质在嗜铬细胞瘤诊断中的应用

目的：探讨间甲肾上腺素类物质（MNs）用酶联免疫法（ELISA）检测在嗜铬细胞瘤诊断中的价值。方法检测疑似嗜铬细胞瘤患者63例及健康人30例（作对照）血MNs,包括甲氧基肾上腺素（NMN）、甲氧基去甲肾上腺素（MN）水平,嗜铬细胞瘤以术后病理诊断为标准。结果63例临床上疑为嗜铬细胞瘤患者中32例经组织学诊断为嗜铬细胞瘤,其中ELISA检测NMN的特异性95%、敏感性91%,MN特异性92%、敏感性72%,NMN和MN二者合并检测特异性97%、敏感性93%。结论血浆游离MNs是诊断嗜铬细胞瘤的有效生化指标,ELISA法作为一种便捷可靠的检测方法,在诊断嗜铬细胞瘤中有着较高的特异性和敏感性。     

Determination of catecholamines and their 3-O-methylated metabolites in urine by mass fragmentography with use of deuterated internal standards.

We report the determination of catecholamines (dopamine, norepinephrine, and epinephrine) and their 3-O-methylated metabolites (3-methoxytyramine, normetanephrine, and metanephrine) in urine by gas chromatography/mass spectrometry, with use of stable isotopically labeled internal standards. Normal excretion values in terms of creatinine, expressed as a function of age, are given, together with results obtained for patients with neuroblastoma, ganglioneuroblastoma, pheochromocytoma, parkinsonism treated with L-DOPA plus peripheral decarboxylase inhibitor, and a patient with cardiogenic shock treated with dopamine. The results obtained for normal adults are discussed in relation to other catecholamine metabolites and mean overall catecholamine turnover.     

Sources and significance of plasma levels of catechols and their metabolites in humans

Human plasma contains several catechols, including the catecholamines norepinephrine, epinephrine, and dopamine, their precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), and their deaminated metabolites, dihydroxyphenylglycol, the main neuronal metabolite of norepinephrine, and dihydroxyphenylacetic acid, a deaminated metabolite of dopamine. Products of metabolism of catechols include 3-methoxytyrosine (from L-DOPA), homovanillic acid and dopamine sulfate (from dopamine), normetanephrine, vanillylmandelic acid, and methoxyhydroxyphenylglycol (from norepinephrine), and metanephrine (from epinephrine). Plasma levels of catechols and their metabolites have related but distinct sources and therefore reflect different functions of catecholamine systems. This article provides an update about plasma levels of catechols and their metabolites and the relevance of those levels to some issues in human health and disease.     

The use of plasma metanephrine to normetanephrine ratio to determine epinephrine poisoning

BACKGROUND: Intravenous epinephrine (EPI) is used as a pharmacologic agent to acutely treat patients in cardiac arrest. Unfortunately, there have been several homicide cases where hospitalized patients died due to a purposeful overdose of epinephrine. We measured plasma epinephrine metabolites (metanephrine, MET, and normetanephrine, NMET) to determine if exogenous epinephrine can be distinguished from endogenous epinephrine concentrations in a controlled animal study. METHODS: Rabbits were subjected to three different protocols. In the physiologic stress group (n=8), rabbits were immobilized for 30 min in a restraining tube. In the sub-lethal dose (n=9), 0.01 mg/kg of epinephrine was injected into anesthetized rabbits. In the lethal dose group (n=8), 1.0 mg/kg of epinephrine was administered into anesthetized rabbits. Blood was collected at regular intervals for up to 480 min. The plasma metanephrine and normetanephrine concentrations were measured by liquid chromatography/mass spectrometry and the serum cortisol concentrations by immunoassay. RESULTS: Serum cortisol and plasma metanephrine and normetanephrine concentrations increased in the stressed animals during immobilization demonstrating the endogenous stress model. Following a sub-therapeutic epinephrine dose, plasma metanephrine increased while plasma normetanephrine decreased. The peak plasma metanephrine concentrations were similar to the concentrations observed in the stressed animals; however, the ratio of plasma metanephrine to normetanephrine was significantly different. In the lethal epinephrine dose, both the plasma metanephrine concentrations and ratio of metabolites were significantly greater than those observed in the endogenously stressed animals. CONCLUSIONS: The ratio of plasma metanephrine to normetanephrine is the best marker to determine the presence of exogenous therapeutic and lethal epinephrine administration. However, there were limitations to the study design that could alter these conclusions.     

Quantification of unconjugated metanephrines in human plasma without interference by acetaminophen

BACKGROUND: Pheochromocytoma is a rare cause of hypertension resulting from increased catecholamine secretion. We aimed to develop a method to measure unconjugated plasma normetanephrine (NMN) and metanephrine (MN) without interference from acetaminophen, a widely prescribed drug for headaches. METHODS: Plasma samples were obtained from 48 subjects (23 males, 25 females; mean age, 49 +/- 14 years; hypertension, n = 37) under resting conditions. Following extraction on solid-phase cation-exchange columns, unconjugated metanephrines were analyzed by HPLC with electrochemical detection and with 4-hydroxy-3-methoxybenzylamine as an internal standard. Catecholamines were measured by HPLC. RESULTS: The assays were linear up to 2000 pg for NMN and for MN. Intraassay imprecisions (CVs) were 4.7% for NMN and 7.0% for MN, and the interassay CV was 12% for both NMN and MN. The limit of detection was 11 fmol for NMN and 17 fmol for MN. Ingestion of acetaminophen or its addition to plasma did not interfere with the MN peaks. Plasma NMN and MN were positively correlated (r = 0.52 and 0.49, respectively; P <0.01 for both) with the respective catecholamines. Plasma NMN (r = 0.27; P = 0.02) but not MN positively correlated with age, whereas only plasma catecholamines (and not metanephrines) were positively correlated (P <0.05) with diastolic blood pressure. CONCLUSIONS: This sensitive MN assay is not affected by simultaneous acetaminophen medication, and reveals a correlation of metanephrines with plasma and urinary catecholamines and age but not with blood pressure.     

A new method for the simultaneous analysis of free and sulfoconjugated normetanephrine, metanephrine, and 3-methoxytyramine in human urine by HPLC with electrochemical detection

A sensitive and specific assay for free and sulfoconjugated normetanephrine, metanephrine, and 3-methoxytyramine was achieved by tetraphenylboron complexing and by high-performance liquid chromatography with electrochemical detection. Sulfoconjugated metabolites were hydrolyzed by sulfatase. Complexing the 3-O-methylated catecholamines with tetraphenylboron followed by their extraction in either and reextraction in dilute hydrochloric acid succeeded in partially purifying the sample without the use of a prepacked column. Detection by electrochemical technique additionally eliminates unoxidable components in the urine. The relatively high sensitivity of this method permits measurement of metabolite concentrations as low as 10 ng/ml, allowing for the first time the determination of free 3-O-methylated catecholamines in human urine. Hydrolysis by sulfatase specifically identifies the form of the conjugated metabolite. The mean total (free plus sulfoconjugated) values of normetanephrine, metanephrine, and 3-methoxytyramine obtained from 25 normal volunteers were 214, 102, and 227 micrograms/day, respectively. Values were greatly increased in patients with pheochromocytoma. The degree of sulfoconjugation varied, and each individual metabolite was highest with normetanephrine (86%). This method is sensitive, rapid, simple, and can be easily standardized for clinical investigation of pheochromocytoma.     

Plasma free and conjugated catecholamines in diagnosis and localisation of pheochromocytoma

In six patients urinary excretion of vanillylmandelic acid and catecholamines (CA) could establish the diagnosis of pheochromocytoma. Free norepinephrine (NE) in plasma was within the normal range in two patients and plasma free epinephrine (E) was only marginally elevated in one of them. The degree of CA conjugation was not altered and scattered as in controls and was therefore not complementary to the usual determination of plasma free CA. The intermittent nature of CA secretion by the tumour could be demonstrated by multiple blood samplings during a 48-h study period in two patients, e.g. normal plasma values might be associated with pheochromocytoma if measurements are made during a trough. Thus a single peripheral CA determination cannot be of discriminative value in the diagnosis of pheochromocytoma unless it shows marked elevation.Ten patients subjected to intracardial measurements and five patients suspected of having a pheochromocytoma underwent venous catheterisation to determine their free and conjugated plasma CA. In controls CA values near the orifices of adrenal veins differed enormously and partly overlapped with corresponding levels of patients with pheochromocytoma. In one patient with surgically proven left adrenal tumour highest concentrations of CA were measured in the vena cava superior. These high CA concentrations, caused by paroxysmal release of CA by the tumour arouse suspicion of an additional, ectopic tumour. Because venous catherisation cannot be relied on implicitly we propose computed tomographic scanning as a first step in localisation of a pheochromocytoma.     

血浆游离甲氧基肾上腺素水平在诊断嗜铬细胞瘤中的价值

目的 探讨酶联免疫分析法(EIA)检测血浆游离甲氧基肾上腺素[3-甲氧基肾上腺素(MN)和3-甲氧基去甲肾上腺素(NM)]诊断嗜铬细胞瘤的价值.方法 病理确诊的30例嗜铬细胞瘤患者和51例高血压患者,用EIA检测血浆MN和NM,结合[3]I-间碘苄胍(MIBG)全身扫描结果进行分析比较.结果 嗜铬细胞瘤组30例患者全身扫描均呈阳性;高血压组中有15例接受全身扫描,结果均呈阴性;嗜铬细胞瘤组MN浓度的中位数为59.3 ng/L,高于高血压组(中位数为33.7 ng/L,Z=-2.440,P<0.05);2组NM浓度的中位数分别为652.0 ng/L和36.3 ng/L,显著高于高血压组(Z=-6.699,P<0.001);2项联合检测(任一或全部阳性)的敏感度、特异度和准确性分别为96.7%(29/30),86.3%(44/51)和90.1%(73/81),联合检测的准确性与全身扫描结果比较,差异无统计学意义(100.0%,P>0.05).结论 EIA法检测血浆游离甲氧基肾上腺素对嗜铬细胞瘤具有较高的诊断效能,有可能替代高压液相层析法而成为该病诊断的首选方法.     

高效液相电化学法检测尿儿茶酚胺和VMA诊断嗜铬细胞瘤

目的 用高效液相电化学法检测尿儿茶酚胺和VMA诊断嗜铬细胞瘤。方法 采用高效液相电化学法检测了64例嗜铬细胞瘤患者和50名健康体检者的尿儿茶酚胺和VMA水平。结果 嗜铬细胞瘤组的肾上腺素、去甲肾上腺素、多巴胺和VMA水平明显高于正常组(P<0.01),64例嗜铬细胞瘤病人中有84.3％的人四个指标全部或个别升高。结论 高效液相电化学检测法可以对肾上腺素、去甲肾上腺素、多巴胺和VMA同时测定,大大提高了嗜铬细胞瘤的诊断水平。     

Gas-liquid chromatographic and mass fragmentographic determination of 3-O-methylated catecholamines in human plasma.

Plasma 3-O-methylated catecholamines, i.e. 3-methoxytyramine, normetanephrine and metanephrine, were separated from catecholamines by passing through alumina and further purified by adsorbing on weakly acidic resin and Amberlite XAD-4. The amines were trifluoroacetylated and determined by gas chromatography or mass fragmentography. Tracer quantities of tritiated 3-MT, NMN or MN were used as internal standards for total recovery estimations. The contents of 3-O-methylated catecholamines in the plasma of normal persons and patients with hyperthyroidism, hypertension, neuroblastoma and pheochromocytoma were measured.     

Plasma free metanephrines for diagnosis of neuroblastoma patients

IntroductionA substantial number of patients with neuroblastoma (NB) have increased excretion of catecholamines and metanephrines. Here, we have investigated the diagnostic role of plasma free metanephrines (PFM), metanephrine (MN), normetanephrine (NMN) and 3-methoxytyramine (3MT) for NB, the most common extra-cranial solid tumour in children.MethodsPFM were quantified by using a commercial IVD-CE LC-MS/MS method on a TSQ Quantiva coupled to an Ultimate 3000. The method was further validated on 103 samples from pediatric subjects (54 patients with histologically confirmed NB and 49 age and sex matched controls). Correlations between PFM concentrations with clinical factors were tested. We directly compared MN, NMN, and 3MT concentrations in matched plasma and urine samples of NB patients (n = 29).Results3MT and NMN showed an excellent diagnostic performance with very high specificity (100% and 95.8%, respectively) and sensitivity (88.2% and 80.4%). ROC curves were obtained (AUC of 0.93 and 0.91 for 3MT and NMN, respectively) and optimal cut-offs that could discriminate between controls and NB patients were defined. A positive correlation between NMN levels in urine and plasma (p = .0017) was found.DiscussionThe determination of plasma 3MT and NMN should be taken in consideration as a new diagnostic tool for NB. Validation in prospective clinical studies in comparison to urinary catecholamines and metanephrines is warranted.