Reference intervals for plasma free metanephrines with an age adjustment for normetanephrine for optimized laboratory testing of phaeochromocytoma

Longitudinal plasma metanephrines preceding pheochromocytoma diagnosis: a retrospective case-control serum repository study

OBJECTIVE

Plasma metanephrines (PMN) are highly sensitive for diagnosis of pheochromocytoma, but the natural history of PMN before pheochromocytoma diagnosis has not been previously described. The aim of the study was to compare the progression of PMN before pheochromocytoma diagnosis to matched healthy and essential hypertension disease controls.

DESIGN

A retrospective case-control Department of Defense Serum Repository (DoDSR) study.

METHODS

We performed a DoDSR study that compared three longitudinal pre-diagnostic PMN for 30 biopsy-proven pheochromocytoma cases to three longitudinal PMN for age, sex, race, and age of serum sample matched healthy and essential hypertension disease controls. Predominant metanephrine (MN) or normetanephrine (NMN) production was identified for each case and converted to a percentage of the upper limit of normal to allow analysis of all cases together. PMN were measured by Quest Diagnostics.

RESULTS

The predominant plasma metanephrine (PPM) was >100 and 300% of the upper limit of normal a median of 6.6 and 4.1 years before diagnosis respectively. A greater percentage of pheochromocytoma patients had a PPM >100 and >300% of the upper limit of normal compared with combined healthy and essential hypertension disease controls <2, 2-8, and >8 years prior to diagnosis. For patients with a baseline PPM 90-300% of the upper limit of normal, a 25% rate of rise per year was 100% specific for pheochromocytoma.

CONCLUSIONS

PPMs elevate years before diagnosis which suggests that delayed diagnoses are common. For mild PMN elevations, follow-up longitudinal PMN trends may provide a highly specific and economical diagnostic tool.

Mass spectrometric quantification of salivary metanephrines-A study in healthy subjects

BACKGROUND

Determination of metanephrine (MN), normetanephrine (NMN), and 3-methoxytyramine (3-MT) in saliva may offer potential diagnostic advantages in diagnosing pheochromocytoma.

METHODS

In this preliminary study, we determined metanephrine concentrations in saliva of healthy subjects and the relationship with simultaneously measured plasma metanephrines. We also studied the possible influence of pre-analytical conditions such as a collection device, awakening, posture, and eating on the salivary metanephrine levels.

RESULTS

Eleven healthy subjects were included. Fasting blood and saliva samples were collected in seated position and after 30min of horizontal rest. Plasma and salivary MN, NMN, and 3-MT concentrations were determined using a high-performance liquid chromatography tandem mass spectrometric technique (LC-MS/MS) with automated solid phase extraction sample preparation. Metanephrines were detectable in saliva from all participants both in seated and supine position. No significant correlations were observed between the MN, NMN, and 3-MT concentrations in saliva and plasma in seated or supine position. Furthermore, there was no difference between MN, NMN, and 3-MT samples collected with or without a collection device.

CONCLUSION

Metanephrines can be detected in saliva with LC-MS/MS with sufficient sensitivity and precision. Our findings warrant evaluation of salivary metanephrine measurement as a novel laboratory tool in the work-up of patients suspected of having a pheochromocytoma.

Urinary and plasma catecholamines and metanephrines in dogs with pheochromocytoma, hypercortisolism, nonadrenal disease and in healthy dogs

Background

Diagnosis of pheochromocytoma (PC) is based on a combination of clinical suspicion, finding an adrenal mass, increased plasma, and urine concentrations of catecholamine metabolites and is finally confirmed with histopathology. In human medicine, it is controversial whether biochemically testing plasma is superior to testing urine.

Objectives

To measure urinary and plasma catecholamines and metanephrines in healthy dogs, dogs with PC, hypercortisolism (HC), and nonadrenal diseases (NAD) and to determine the test with the best diagnostic performance for dogs with PC.

Animals

Seven PC dogs, 10 dogs with HC, 14 dogs with NAD, 10 healthy dogs.

Methods

Prospective diagnostic clinical study. Urine and heparin plasma samples were collected and stored at −80°C before analysis using high‐pressure liquid chromatography (HPLC) coupled to electrochemical detection or tandem mass spectrometry were performed. Urinary variables were expressed as ratios to urinary creatinine concentration.

Results

Dogs with PC had significantly higher urinary normetanephrine and metanephrine : creatinine ratios and significantly higher plasma‐total and free normetanephrine and plasma‐free metanephrine concentrations compared to the 3 other groups. There were no overlapping results of urinary normetanephrine concentrations between PC and all other groups, and only one PC dog with a plasma normetanephrine concentration in the range of the dogs with HC and NAD disease. Performances of total and free plasma variables were similar. Overlap of epinephrine and norepinephrine results between the groups was large with both urine and plasma.

Conclusion and clinical importance

Measurement of normetanephrine is the preferred biochemical test for PC and urine was superior to plasma.

Urinary clonidine suppression testing for the diagnosis of pheochromocytoma

OBJECTIVE

The diagnosis of pheochromocytoma/paraganglioma (PPGL) involves detection of elevated levels of plasma and/or 24-h urine catecholamines and/or their metabolites, including metanephrines. Although these tests are reasonably sensitive, false-positive results are often encountered. Follow-up tests can provide additional information to correctly diagnose PPGL. In this regard, the utility of the urinary clonidine suppression test (UCST) remains unknown.

METHODS

To assess the diagnostic accuracy of the UCST in confirming or excluding PPGL, we conducted a retrospective analysis of all patients who underwent a UCST between 2000 and 2013 (n = 59; 15 PPGLs) at a single centre. Twelve-hour urine catecholamines and metanephrines were assessed before and after clonidine administration, and examined in relation to final diagnosis, PPGL or non-PPGL. Receiver operating characteristic analyses were used to identify optimal positivity cut-offs. Sensitivity, specificity, positive and negative predictive values were calculated.

RESULTS

Clonidine significantly decreased urine creatinine-corrected norepinephrine and normetanephrine in patients without PPGL (P < 0.001 pairwise) but not in patients with PPGL. Epinephrine and metanephrine levels were not significantly reduced in either group. Receiver operating characteristic (ROC) area under the curve was 0.955 [95% confidence interval (95% CI) 0.906-1.000, P < 0.001] and 0.823 (95% CI 0.706-0.940, P < 0.001) for norepinephrine and normetanephrine, respectively. Optimal cut-offs were established at 50 and 15% reductions in norepinephrine and normetanephrine, respectively, which provided high sensitivities (93.3% for both) and negative predictive values (97.4 and 96.3%). When both were concordant, higher diagnostic accuracy was achieved (100% sensitivity, 92.0% specificity). Results were similar in subgroups of individuals with borderline initial testing (n = 40) or on interfering drugs (n = 25).

CONCLUSION

The UCST appears to be a highly accurate test for PPGL. Further prospective studies are needed to validate these results before routine use is encouraged.

Measurements of plasma metanephrines by immunoassay vs liquid chromatography with tandem mass spectrometry for diagnosis of pheochromocytoma

BACKGROUND

Reports conflict concerning measurements of plasma metanephrines (MNs) for diagnosis of pheochromocytomas/paragangliomas (PPGLs) by immunoassays compared with other methods. We aimed to compare the performance of a commercially available enzyme-linked immunoassay (EIA) kit with liquid chromatography-tandem mass spectrometric (LC-MS/MS) measurements of MNs to diagnose PPGLs.

METHODS

In a substudy of a prospective, multicenter trial to study the biochemical profiles of monoamine-producing tumors, we included 341 patients (174 males and 167 females) with suspected PPGLs (median age 54 years), of whom 54 had confirmed PPGLs. Plasma MNs were measured by EIA and LC-MS/MS, each in a specialized laboratory.

RESULTS

Plasma normetanephrine (NMN) and MN were measured 60 and 39% lower by EIA than by LC-MS/MS. Using upper cut-offs stipulated for the EIA, diagnostic sensitivity was only 74.1% at a specificity of 99.3%. In contrast, use of similar cut-offs for MN and overall lower age-adjusted cut-offs for NMN measured by LC-MS/MS returned a diagnostic sensitivity and specificity of 98.1 and 99.7%. Areas under receiver-operating characteristic curves, nevertheless, indicated comparable diagnostic performance of the EIA (0.993) and LC-MS/MS (0.985). Diagnostic sensitivity for the EIA increased to 96.2% with a minimal loss in specificity (95.1%) following use of cut-offs for the EIA adapted to correct for the negative bias.

CONCLUSIONS

The EIA underestimates plasma MNs and diagnostic sensitivity is poor using commonly stipulated cut-offs, resulting in a high risk for missing patients with PPGLs. Correction of this shortcoming can be achieved by appropriately determined cut-offs resulting in comparable diagnostic performance of EIA and LC-MS/MS assays.

Diagnostic accuracy of plasma free metanephrines in a seated position compared with 24-hour urinary metanephrines in the investigation of pheochromocytoma

The aim of this study was to determine the diagnostic efficacy of free metanephrines in plasma samples drawn in the seated position compared with 24-h urinary metanephrines in detecting pheochromocytomas in Asian patients. This prospective study was conducted at Samsung Medical Center between May 2010 and July 2011. The study contained 245 subjects, including 28 patients with histologically-proven pheochromocytoma, 44 with histologically-proven non-pheochromocytoma, 112 controls suspected of having tumors but with negative investigations during two or more years of follow-up, and 45 healthy normotensive volunteers. Plasma-free metanephrines were measured by LC-MS/MS. The cut-off values with optimal sensitivity and specificity for plasma metanephrine and plasma normetanephrine were 0.33 nmol/L and 0.61 nmol/L, respectively. Both the plasma metanephrines measurement and urinary metanephrines measurement had a sensitivity of 96.4% (p = 1.00). However, the urinary metanephrines measurement was significantly more specific than the plasma metanephrines measurement (94.2% vs. 75.6%; p < 0.001). When we applied cut-off values based on BMI, specificity improved from 75.6% to 87.2%, with a comparable gain in sensitivity. From a diagnostic perspective, measurement of free metanephrines in plasma drawn in the seated position is highly sensitive but insufficiently specific when compared with measurement of 24-h urinary fractionated metanephrines. The specificity may be improved by applying cut-off values based on BMI. We suggest that free metanephrines in plasma drawn from seated position can also be used as an initial screening test to ensure that pheochromocytomas are not missed in Asian patients.

Pathophysiology and diagnosis of disorders of the adrenal medulla: focus on pheochromocytoma

The principal function of the adrenal medulla is the production and secretion of catecholamines. During stressful challenging conditions, catecholamines exert a pivotal homeostatic role. Although the main adrenomedullary catecholamine, epinephrine, has a wide array of adrenoreceptor-mediated effects, its absence does not cause life-threatening problems. In contrast, excess production of catecholamines due to an adrenomedullary tumor, specifically pheochromocytoma, results in significant morbidity and mortality. Despite being rare, pheochromocytoma has a notoriously bad reputation because of its potential devastating effects if undetected and untreated. The paroxysmal signs and symptoms and the risks of missing or delaying the diagnosis are well known for most physicians. Nevertheless, even today the diagnosis is still overlooked in a considerable number of patients. Prevention and complete cure are however possible by early diagnosis and appropriate treatment but these patients remain a challenge for physicians. Yet, biochemical proof of presence or absence of catecholamine excess has become more easy and straightforward due to developments in assay methodology. This also applies to radiological and functional imaging techniques for locating the tumor. The importance of genetic testing for underlying germline mutations in susceptibility genes for patients and relatives is increasingly recognized. Yet, the effectiveness of genetic testing, in terms of costs and benefits to health, has not been definitively established. Further improvement in knowledge of genotype-phenotype relationships in pheochromocytoma will open new avenues to a more rationalized and personalized diagnostic approach of affected patients.

Pheochromocytoma

Pheochromocytoma and paraganglioma are catecholamine-producing tumors that are associated with substantial serious morbidity and mortality. A carefully taken medical history and early consideration of such tumors are key for early diagnosis and treatment. The biochemical diagnosis should include measurements of metanephrines in either plasma or urine. In addition to anatomical imaging, sensitive functional imaging modalities offer extra benefit for most patients in locating the tumor and eventual metastases. In at least 30% of all patients with a pheochromocytoma/paraganglioma, an underlying germline is responsible for tumor development and genetic testing should be considered in all patients. Current treatment options for malignant pheochromocytoma/paraganglioma are still very modest. New developments in the therapeutic armamentarium may improve the prospect for these patients.

Laboratory evaluation of pheochromocytoma and paraganglioma

BACKGROUND

Pheochromocytomas and paragangliomas (PPGLs) are potentially lethal yet usually surgically curable causes of endocrine hypertension; therefore, once clinical suspicion is aroused it is imperative that clinicians choose the most appropriate laboratory tests to identify the tumors.

CONTENT

Compelling evidence now indicates that initial screening for PPGLs should include measurements of plasma free metanephrines or urine fractionated metanephrines. LC-MS/MS offers numerous advantages over other analytical methods and is the method of choice when measurements include methoxytyramine, the O-methylated metabolite of dopamine. The plasma test offers advantages over the urine test, although it is rarely implemented correctly, rendering the urine test preferable for mainstream use. To ensure optimum diagnostic sensitivity for the plasma test, reference intervals must be established for blood samples collected after 30 min of supine rest and after an overnight fast when measurements include methoxytyramine. Similarly collected blood samples during screening, together with use of age-adjusted reference intervals, further minimize false-positive results. Extents and patterns of increases in plasma normetanephrine, metanephrine, and methoxytyramine can additionally help predict size and adrenal vs extraadrenal locations of tumors, as well as presence of metastases and underlying germline mutations of tumor susceptibility genes.

SUMMARY

Carried out correctly at specialist endocrine centers, collection of blood for measurements of plasma normetanephrine, metanephrine, and methoxytyramine not only provides high accuracy for diagnosis of PPGLs, but can also guide clinical decision-making about follow-up imaging strategies, genetic testing, and therapeutic options. At other centers, measurements of urine fractionated metanephrines will identify most PPGLs.

A novel method for the measurement of plasma metanephrines using online solid phase extraction-liquid chromatography tandem mass spectrometry

Background

Measurement of plasma metanephrine, normetanephrine and 3-methoxytyramine is useful in the diagnosis of phaeochromocytomas, but many assays require a large volume of plasma due to poor assay sensitivity, and often require lengthy sample preparation. Our aim was to develop a method for measurement of plasma metanephrines using a small sample volume with minimal hands-on preparation.

Methods

Samples were deproteinised using 10 K spin filters prior to online solid phase extraction using a Waters Acquity UPLC Online SPE Manager (Waters, Manchester, UK) coupled to a Waters Xevo TQ-S mass spectrometer (Waters, Manchester, UK). The assay was validated and results compared to a previously published method.

Results

We achieved a limit of quantification of 37.5 pmol/L for metanephrine and 3-methoxytyramine and 75 pmol/L for normetanephrine using only 150  µL of sample. The assay was linear up to 30,000 pmol/L for all analytes and in a method comparison study results showed good agreement with a previously published LC-MS/MS assay.

Conclusions

We have developed a simple method for measurement of plasma metanephrine, normetanephrine and 3-methoxytyramine using only 150  µL of sample. There is minimal hands-on sample preparation required and the assay is suitable for routine use in a clinical laboratory.

Pheochromocytoma and paraganglioma: an endocrine society clinical practice guideline

OBJECTIVE

The aim was to formulate clinical practice guidelines for pheochromocytoma and paraganglioma (PPGL).

PARTICIPANTS

The Task Force included a chair selected by the Endocrine Society Clinical Guidelines Subcommittee (CGS), seven experts in the field, and a methodologist. The authors received no corporate funding or remuneration.

EVIDENCE

This evidence-based guideline was developed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system to describe both the strength of recommendations and the quality of evidence. The Task Force reviewed primary evidence and commissioned two additional systematic reviews.

CONSENSUS PROCESS

One group meeting, several conference calls, and e-mail communications enabled consensus. Committees and members of the Endocrine Society, European Society of Endocrinology, and Americal Association for Clinical Chemistry reviewed drafts of the guidelines.

CONCLUSIONS

The Task Force recommends that initial biochemical testing for PPGLs should include measurements of plasma free or urinary fractionated metanephrines. Consideration should be given to preanalytical factors leading to false-positive or false-negative results. All positive results require follow-up. Computed tomography is suggested for initial imaging, but magnetic resonance is a better option in patients with metastatic disease or when radiation exposure must be limited. (123)I-metaiodobenzylguanidine scintigraphy is a useful imaging modality for metastatic PPGLs. We recommend consideration of genetic testing in all patients, with testing by accredited laboratories. Patients with paraganglioma should be tested for SDHx mutations, and those with metastatic disease for SDHB mutations. All patients with functional PPGLs should undergo preoperative blockade to prevent perioperative complications. Preparation should include a high-sodium diet and fluid intake to prevent postoperative hypotension. We recommend minimally invasive adrenalectomy for most pheochromocytomas with open resection for most paragangliomas. Partial adrenalectomy is an option for selected patients. Lifelong follow-up is suggested to detect recurrent or metastatic disease. We suggest personalized management with evaluation and treatment by multidisciplinary teams with appropriate expertise to ensure favorable outcomes.

Biochemical diagnosis of phaeochromocytoma using plasma-free normetanephrine, metanephrine and methoxytyramine: importance of supine sampling under fasting conditions

OBJECTIVE

To document the influences of blood sampling under supine fasting versus seated nonfasting conditions on diagnosis of phaeochromocytomas and paragangliomas (PPGL) using plasma concentrations of normetanephrine, metanephrine and methoxytyramine.

DESIGN AND METHODS

Biochemical testing for PPGL was performed on 762 patients at six centres, two of which complied with requirements for supine sampling after an overnight fast and four of which did not. Phaeochromocytomas and paragangliomas were found in 129 patients (67 noncompliant, 62 compliant) and not in 633 patients (195 noncompliant, 438 compliant).

RESULTS

Plasma concentrations of normetanephrine and methoxytyramine did not differ between compliant and noncompliant sampling conditions in patients with PPGL but were 49-51% higher in patients without PPGL sampled under noncompliant compared with compliant conditions. The 97·5 percentiles of distributions were also higher under noncompliant compared with compliant conditions for normetanephrine (1·29 vs 0·79 nmol/l), metanephrine (0·49 vs 0·41 nmol/l) and methoxytyramine (0·42 vs 0·18 nmol/l). Use of upper cut-offs established from seated nonfasting sampling conditions resulted in substantially decreased diagnostic sensitivity (98% vs 85%). In contrast, use of upper cut-offs established from supine fasting conditions resulted in decreased diagnostic specificity for testing under noncompliant compared with compliant conditions (71% vs 95%).

CONCLUSIONS

High diagnostic sensitivity of plasma normetanephrine, metanephrine and methoxytyramine for the detection of PPGL can only be guaranteed using upper cut-offs of reference intervals established with blood sampling under supine fasting conditions. With such cut-offs, sampling under seated nonfasting conditions can lead to a 5·7-fold increase in false-positive results necessitating repeat sampling under supine fasting conditions.

Seasonal variation in plasma free normetanephrine concentrations: implications for biochemical diagnosis of pheochromocytoma

BACKGROUND

Higher plasma concentrations of catecholamines in winter than in summer have been established, but whether this impacts the plasma concentrations of metanephrines used for the diagnosis of pheochromocytoma is unknown.

OBJECTIVE

In this study, we examined seasonal variations in the plasma concentrations of metanephrines, the impact of this on diagnostic test performance and the influences of forearm warming ('arterialization' of venous blood) on blood flow and measured concentrations.

METHODS

The measurements of the plasma concentrations of metanephrines were recorded from 4052 patients tested for pheochromocytoma at two clinical centers. Among these patients, 107 had tumors. An additional 26 volunteers were enrolled for the measurements of plasma metanephrines and forearm blood flow before and after forearm warming.

RESULTS

There was no seasonal variation in the plasma concentrations of metanephrines among patients with pheochromocytoma, whereas among those without tumors, the plasma concentrations of normetanephrine were higher (P<0.0001) in winter than in summer. Lowest concentrations of normetanephrine were measured in July, with those recorded from December to April being more than 21% higher (P<0.0001). These differences resulted in a twofold higher (P=0.0012) prevalence of false-positive elevations of normetanephrine concentrations in winter than in summer, associated with a drop in overall diagnostic specificity from 96% in summer to 92% in winter (P=0.0010). Forearm warming increased blood flow and lowered (P=0.0020) plasma normetanephrine concentrations.

CONCLUSIONS

The plasma concentrations of normetanephrine are subject to seasonal variation with a resulting higher prevalence of false-positive results in winter than in summer. Lowered plasma concentrations of normetanephrine with forearm warming suggest an effect of temperature. These results have implications for considerations of temperature to minimize false-positive results.

Diagnosis of endocrine disease: Biochemical diagnosis of phaeochromocytoma and paraganglioma

Adrenal phaechromocytomas and extra-adrenal sympathetic paragangliomas (PPGLs) are rare neuroendocrine tumours, characterised by production of the catecholamines: noradrenaline, adrenaline and dopamine. Tumoural secretion of catecholamines determines their clinical presentation which is highly variable among patients. Up to 10-15% of patients present entirely asymptomatic and in 5% of all adrenal incidentalomas a PPGL is found. Therefore, prompt diagnosis of PPGL remains a challenge for every clinician. Early consideration of the presence of a PPGL is of utmost importance, because missing the diagnosis can be devastating due to potential lethal cardiovascular complications of disease. First step in diagnosis is proper biochemical analysis to confirm or refute the presence of excess production of catecholamines or their metabolites. Biochemical testing is not only indicated in symptomatic patients but also in asymptomatic patients with adrenal incidentalomas or identified genetic predispositions. Measurements of metanephrines in plasma or urine offer the best diagnostic performance and are the tests of first choice. Paying attention to sampling conditions, patient preparation and use of interfering medications is important, as these factors can largely influence test results. When initial test results are inconclusive, additional tests can be performed, such as the clonidine suppression test. Test results can also be used for estimation of tumour size or prediction of tumour location and underlying genotype. Furthermore, tumoural production of 3-methoxytyramine is associated with presence of an underlying SDHB mutation and may be a biomarker of malignancy.

Pheochromocytoma: pitfalls in the biochemical evaluation

The current work-up of a patient suspected to have a pheochromocytoma starts with the measurement of plasma or urine metanephrines. Notably, up to a quarter of these patients will have a false positive result. When the plasma or urine metanephrines are less than the 4-fold upper limit of normal, clinicians struggle between the fear of missing a potentially fatal condition and ordering costly follow up tests. In many cases, ordering unnecessary imaging studies may only increase the level of patient anxiety. This article will review various physiologic factors, pathologic conditions and medications that may influence the levels of catecholamines and their metabolites yielding false positive or false negative results. Acquiring familiarity with these conditions as well as interfering medications will equip clinicians with better interpretation skills of the biochemical tests.

LC–MS/MS in endocrinology: what is the profit of the last 5 years?

Currently, chromatography (GC but more commonly HPLC) is the analytical method of choice for several hormones, either because the immunoassays suffer from extensive crossreactivity or because chromatography permits simultaneous measurements of hormones. However, sometimes the conventional detection systems with HPLC methods do not meet desired specificity. With the increase of robust and affordable LC–MS/MS systems, the next step forward in specificity was taken. LC–MS/MS is rapidly being incorporated in the endocrine laboratories. To be useful in the clinical diagnostic practice, it is of utmost importance that methods are both analytically and clinically vaidated, as until now, the majority of applications of LC–MS/MS in the clinical laboratories are ‘home-made’ methods, therefore special case must be taken. This review aims to focus on Clinical and Laboratory Standards Institute or comparable validated LC–MS/MS methods for targeted hormone analysis used for diagnostic purposes in human samples, published in the last 5 years.

Levodopa therapy in Parkinson's disease: influence on liquid chromatographic tandem mass spectrometric-based measurements of plasma and urinary normetanephrine, metanephrine and methoxytyramine

BACKGROUND

Medication-related interferences with measurements of catecholamines and their metabolites represent important causes of false-positive results during diagnosis of phaeochromocytomas and paragangliomas (PPGLs). Such interferences are less troublesome with measurements by liquid chromatography with tandem mass-spectrometry (LC-MS/MS) than by other methods, but can still present problems for some drugs. Levodopa, the precursor for dopamine used in the treatment of Parkinson's disease, represents one potentially interfering medication.

METHODS

Plasma and urine samples, obtained from 20 Parkinsonian patients receiving levodopa, were analysed for concentrations of catecholamines and their O-methylated metabolites by LC-MS/MS. Results were compared with those from a group of 120 age-matched subjects and 18 patients with PPGLs.

RESULTS

Plasma and urinary free and deconjugated (free + conjugated) methoxytyramine, as well as urinary dopamine, showed 22- to 148-fold higher (P < 0.0001) concentrations in patients receiving levodopa than in the reference group. In contrast, plasma normetanephrine, urinary noradrenaline and urinary free and deconjugated normetanephrine concentrations were unaffected. Plasma free metanephrine, urinary adrenaline and urinary free and deconjugated metanephrine all showed higher (P < 0.05) concentrations in Parkinsonian patients than the reference group, but this was only a problem for adrenaline. Similar to normetanephrine, plasma and urinary metanephrine remained below the 97.5 percentiles of the reference group in almost all Parkinsonian patients.

CONCLUSIONS

These data establish that although levodopa treatment confounds identification of PPGLs that produce dopamine, the therapy is not a problem for use of LC-MS/MS measurements of plasma and urinary normetanephrine and metanephrine to diagnose more commonly encountered PPGLs that produce noradrenaline or adrenaline.