Update (June 19, 2026): Point-of-Care vs Reference Lab Phenobarbital Levels Disagree in Dogs and Cats - Method Comparison

TL;DR

A dual-institution study found a point-of-care analyzer and a reference laboratory disagreed meaningfully on plasma phenobarbital concentrations in dogs and cats, with the point-of-care device reading systematically higher and altering clinical interpretation in nearly a third of cases.

What just dropped

• A retrospective study compared paired plasma phenobarbital measurements from the same blood samples on an on-site point-of-care analyzer (Catalyst One) and an off-site reference laboratory analyzer (Cobas 6000) in dogs and cats (Scherf 2025, https://europepmc.org/articles/PMC12587887).
• Across 33 paired measurements, the two analyzers were not equivalent and showed poor agreement (concordance correlation coefficient 0.74).
• The point-of-care analyzer read systematically higher, with a mean positive bias of +22.50 micromol/L versus the reference laboratory.
• Discrepancies in medical interpretation occurred in 30.3% of cases when manufacturer-specific thresholds were applied.

Context

Therapeutic drug monitoring underpins safe phenobarbital use, where the gap between effective and toxic concentrations is narrow. Monitoring also matters across the wider antiseizure-drug class: in a separate cohort, phenobarbital co-administration significantly lowered serum levetiracetam concentrations, so the accuracy of any single measurement can ripple through multidrug decisions (Saint-Maxent 2024, https://europepmc.org/articles/PMC11256123). If a point-of-care device reads consistently higher, a clinician could wrongly judge a patient to be at the top of, or above, the target range and reduce a dose unnecessarily.

What this changes in the epilepsy-monitoring picture

Our potassium bromide and canine epilepsy review (https://www.thevoyage.ai/forvets/knowledge/potassium-bromide-dogs-idiopathic-epilepsy) stresses therapeutic drug monitoring for antiseizure agents. This study adds an analytical-method caveat: clinicians should be cautious interpreting phenobarbital levels when switching between point-of-care and reference-laboratory analyzers during ongoing monitoring, and ideally track a given patient on a consistent method. The cohort was small and retrospective, so the finding flags a real-world pitfall rather than defining a correction factor.

References

1. Scherf G, Van Caenegem N. 2025. Agreement between a point-of-care analyzer and a reference laboratory analyzer for plasma phenobarbital quantification in dogs and cats. Open Vet J 15(9):4716-4725. https://europepmc.org/articles/PMC12587887
2. Saint-Maxent M, Juette T, Parent J, Castel A, Parmentier T. 2024. Factors influencing serum concentrations of levetiracetam in dogs with epilepsy. J Vet Intern Med 38(4):2249-2256. https://europepmc.org/articles/PMC11256123

Voyage Clinical Desk

From clinical question to SOAP draft — cited differentials, live dose calculators, owner handouts. Trained on the veterinary canon (Plumb's, Ettinger, JVIM, ACVIM consensus, 50,000+ indexed references). First answer free, no signup.

Open Voyage Clinical Desk: https://www.thevoyage.ai/forvets/ask?context=update-2026-06-19-phenobarbital-poc-tdm-accuracy

Related reads

• Potassium Bromide (KBroVet) for Canine Idiopathic Epilepsy: FDA Full Approval and Clinical Evidence
• Zonisamide for Canine Idiopathic Epilepsy: Efficacy, Tolerability, and Therapeutic Drug Monitoring