Hypophosphataemia as a biomarker in seizures evaluated in the first seizure clinic and liaison neurology

<h3>Introduction</h3> Seizures are a leading cause of neurology referrals. Recently, hypophosphataemia has emerged as a potential biomarker of epileptic seizures compared to other causes of transient loss of consciousness (TLOC). We audited the frequency with which phosphate was captured in possible seizure presentations and its clinical utility. <h3>Methods</h3> Cases, identified retrospectively, were referrals to a first seizure clinic (2021–2023), or liaison neurology (Feb-June 2023). Haematological parameters, electrolytes, lactate, glucose, and C- reactive protein were collated. Each episode was assigned ‘seizure’ or ‘other’ through notes review independent of serological findings. Statistical analysis was conducted in R (v4.0.3). <h3>Results</h3> 182 episodes (91 each first fit/liaison, 126 (69%) seizures) from 173 patients (78 women, mean age 51) were analysed. Phosphate was measured in 91 (50%) encounters. After multiple comparison correction, only phosphate (p=0.046) and lactate (p=0.038) significantly differentiated seizure from other TLOC causes. Mean phosphate was 0.98 mmol/L (range 0.42–1.54) in epileptic seizures and 1.19 mmol/L (0.66–2.13) in non-seizure events. A phosphate &lt;0.8 (lower limit of normal) was present in 26.5% (17/64) seizures and 7.4% (2/27) non-seizure episodes (p=0.049). <h3>Conclusions</h3> Phosphate may be a useful seizure biomarker, but is infrequently captured in routine practice. Prospective studies should investigate its role in differentiating TLOC episodes.