Adenosine concentration in patients with neurally-mediated syncope

<strong>Background.</strong> Either high or low values of adenosine blood level (ABL) can differentiate some forms of neurally-mediated syncope (NMS). A rapid method of measurement has recently been developed. The aim of the present study was: 1) to compare ABLs in an unselected population of consecutive patients referred for evaluation of suspected NMS syncope and in healthy controls; and 2) to assess the relative prevalence of low and high adenosine forms among an unselected syncope population <strong>Method.</strong> Whole blood was collected after finger puncture and its concentration was measured by liquid chromatography /mass spectrometry (LC-MS/MS). <strong>Results. </strong>Among 89 control subjects, the median ABL value was 0.54 µM (IQR 0.46-0.65). The lowest 5% and the upper 95% percentile were 0.40 and 0.80 µM respectively. Compared with healthy subjects, the 146 syncope patients showed on average a higher median ABL value (0.63 [IQR 0.45-0.73, p=0.04) and a larger distribution of values. Low ABL values below the 5^th percentile were observed in 28 (19%) patients and in 5 controls, p=0.003 and high ABL values were observed in 26 (18%) patients and 5 controls, p=0.009. <strong>Conclusions. </strong>ABL is different in patients with suspected NMS than in healthy subjects. Patients with low and high adenosine values account for 19% and 18% of the general population. Thus, low and high ABL limits, as defined in this study, may help to define the purinergic profile of an unselected subjects with a clinical diagnosis of suspected NMS.