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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 30 min 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. [ABSTRACT FROM AUTHOR]

Objectives Analysis of serum/plasma methylmalonic acid (MMA) is important for the diagnosis and management of methylmalonic acidemia in pediatric populations. This work focuses on developing and validating a liquid chromatography tandem mass spectrometry (LC-MS/MS) method to monitor methylmalonic acidemia using a simple method preparation. Design and methods MMA and stable isotope labeled d 3 -MMA was extracted using supported liquid extraction (SLE). Assay imprecision, bias, linearity, recovery and carryover were determined. The relationship between MMA and propionyl acylcarnitine (C3-acylcarnitine) was also evaluated using historical paired results from 51 unique individuals. Results Baseline separation between MMA and succinic acid was completed in 7 min. The assay was linear from 0.1 to 500 μM. The intra-day and inter-day imprecision CV ranged from 4.1 to 13.2% (0.3 to 526 μM) and 5.0 to 15.7% (0.3 to 233 μM), respectively. Recovery ranged from 93 to 125%. The correlation with a national reference laboratory LC-MS/MS assay showed a Deming regression of 1.026 and intercept of − 1.335. Carryover was determined to be < 0.04%. Patient-specific correlation was observed between MMA and C3-acylcarnitine. Conclusion This report describes the first LC-MS/MS method using SLE for MMA extraction. In addition, we illustrate the challenges encountered during this method development that should be assessed and resolved by any laboratory implementing a SLE LC-MS/MS assay designed to quantify analytes across several orders of magnitude. [ABSTRACT FROM AUTHOR]