Properly Collected Plasma Metanephrines Excludes PPGL After False-Positive Screening Tests

Pitfalls in the Diagnostic Evaluation of Pheochromocytomas

Pheochromocytomas and paragangliomas (PPGLs), rare neuroendocrine tumors arising from chromaffin cells, present a significant diagnostic challenge due to their clinical rarity and polymorphic symptomatology. The clinical cases demonstrate the importance of an integrated approach that combines clinical assessment, biochemical testing, and imaging to distinguish PPGLs from mimicking conditions, such as obstructive sleep apnea and interfering medication effects, which can lead to false-positive biochemical results. Although a rare condition, false-negative metanephrine levels can occur in pheochromocytomas, but imaging findings can give some clues and increase suspicion for a pheochromocytoma diagnosis. This expert endocrine consult underscores the critical role of evaluating preanalytical conditions and pretest probability in the biochemical diagnosis of PPGLs. Moreover, a careful differentiation of PPGLs from similar conditions and careful selection and interpretation of diagnostic tests, with focus on understanding and reducing false positives to enhance diagnostic accuracy and patient outcomes, is crucial.

The utility of rested prolactin sampling in the evaluation of hyperprolactinaemia

BACKGROUND AND AIMS

Serum prolactin levels may be elevated by venepuncture stress. We investigated the utility of a rested prolactin sample, obtained through an indwelling venous cannula, in preventing the overdiagnosis of hyperprolactinaemia.

METHODS

Patients at our institution undergo serial prolactin sampling, usually over 40 min, when investigating hyperprolactinaemia. We retrospectively reviewed all serial prolactin sampling performed during a 3-year period. Patients with possible medication-induced hyperprolactinaemia and macroprolactin interference were excluded. We assessed the effect of venepuncture-associated stress on hyperprolactinaemia with the main outcome being normalisation of serum prolactin at the end of serial sampling.

RESULTS

Ninety-three patients with documented hyperprolactinaemia (range 360-1690 mU/L) were included in the analysis. Prolactin decreased during serial sampling in 73 patients (78%), suggesting a prevalent effect of venepuncture stress. The final prolactin sample was normal in 50 patients (54%), consistent with stress hyperprolactinaemia rather than pathological hyperprolactinaemia. Patients with a referral prolactin result greater than two times the upper reference limit (URL) were less likely (15%) to have a normal prolactin result on serial sampling. Measurement of a single rested prolactin sample from an indwelling cannula showed the same diagnostic utility as serial sampling.

CONCLUSION

Serum prolactin results are frequently elevated by the stress of venepuncture. Confirmation of pathological hyperprolactinaemia in a rested sample obtained from an indwelling venous cannula is recommended in patients with mild hyperprolactinaemia, particularly when the referral prolactin is less than two times the URL.

Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

A Laboratory Medicine Perspective on the Investigation of Phaeochromocytoma and Paraganglioma

Phaeochromocytomas (PC) and sympathetic paragangliomas (PGL) are potentially malignant tumours arising from the adrenal medulla (PC) or elsewhere in the sympathetic nervous system (PGL). These tumours usually secrete catecholamines and are associated with significant morbidity and mortality, so accurate and timely diagnosis is essential. The initial diagnosis of phaeochromocytoma/paraganglioma (PPGL) is often dependent on biochemical testing. There is a range of pre-analytical, analytical and post-analytical factors influencing the analytical and diagnostic performance of biochemical tests for PPGL. Pre-analytical factors include patient preparation, sample handling and choice of test. Analytical factors include choice of methodology and the potential for analytical interference from medications and other compounds. Important factors in the post-analytical phase include provision of appropriate reference ranges, an understanding of the potential effects of various medications on metanephrine concentrations in urine and plasma and a consideration of PPGL prevalence in the patient population being tested. This article reviews these pre-analytical, analytical and post-analytical factors that must be understood in order to provide effective laboratory services for biochemical testing in the diagnosis of PPGL.

Perioperative Management of Pheochromocytomas and Sympathetic Paragangliomas

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors arising from chromaffin cells of the adrenal medulla or extra-adrenal paraganglia, respectively. PPGLs have the highest degree of heritability among endocrine tumors. Currently, ~40% of individuals with PPGLs have a genetic germline and there are at least 12 different genetic syndromes related to these tumors. Metastatic PPGLs are defined by the presence of distant metastases at sites where chromaffin cells are physiologically absent. Approximately 10% of pheochromocytomas and ~40% of sympathetic paragangliomas are linked to metastases, explaining why complete surgical resection is the first-choice treatment for all PPGL patients. The surgical approach is a high-risk procedure requiring perioperative management by a specialized multidisciplinary team in centers with broad expertise. In this review, we summarize and discuss the most relevant aspects of perioperative management in patients with pheochromocytomas and sympathetic paragangliomas.