Primary aldosteronism (PA) is a common and likely under-diagnosed cause of secondary hypertension with associated cardiovascular morbidity and mortality. Current diagnosis comprises screening, confirmatory testing and sub-type classification (lateralisation) to distinguish unilateral disease (requiring surgery) from bilateral disease (requiring medical management). This multi-step process is complex and variable with a lack of uniformity in diagnostic protocols, standardised/reference assay methodologies, and diagnostic thresholds. There is evidence in the literature that targeted serum steroid panels may have a role in diagnosis of PA, and both targeted steroid panels and untargeted metabolomics in serum and urine are a promising area of research. This study aims to identify and recruit participants (n=40; 20 with confirmed PA and 20 with other causes of hypertension) willing to donate lithium heparin plasma for a metabolomics pilot study. This plasma will be interrogated through untargeted metabolomics using gas/liquid chromatography-mass-spectrometric methods and computational data processing to allow power calculations and inform experimental design for future studies. The utility of metabolites from the metabolomics dataset will be evaluated by comparison against current biomarkers for screening, diagnosis and lateralisation as well as radiology and histology acquired through routine diagnostic work-up. The long-term aim for larger studies is to identify suitable candidate analytes in plasma for future development into targeted, clinically-useful analyte panels.