skip to main content

Wada Test – Language and Memory Lateralisation — SCE Neurology MCQ

Instant feedback + full explanation. One question, done properly.

HardEpilepsy & Seizure DisordersWada Test – Language and Memory LateralisationSCE Neurology

A cachectic patient taking phenytoin has horizontal nystagmus, dysarthria and gait ataxia. Albumin is 18 g/L, estimated GFR is 22 mL/min and total phenytoin is 7 mg/L. Which laboratory result would most reliably determine whether the symptoms represent phenytoin toxicity?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — A directly measured unbound phenytoin concentration

Explanation lettering: B = shown as A · D = shown as B · E = shown as D · A = shown as E

A repeats the misleading protein-bound measure. B is correct: severe hypoalbuminaemia and uraemia increase the active free fraction, so a low total concentration can coexist with toxic unbound exposure; direct free measurement is preferred. C reflects enzyme induction but not active phenytoin exposure. D is not a validated toxicity assay. E measures the wrong drug.

Reference: Phenytoin toxicity in hypoalbuminaemia: https://pmc.ncbi.nlm.nih.gov/articles/PMC9660550/ NHS Highland: phenytoin dose calculations: https://www.rightdecisions.scot.nhs.uk/tam-treatments-and-medicines-nhs-highland/adult-therapeutic-guidelines/nervous-system/seizures-guidelines/phenytoin-dose-calculations-guidelines/