Submitted:
22 December 2025
Posted:
23 December 2025
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Abstract
Background/Objectives: Lamotrigine is an anticonvulsant and mood stabilizer with wide interindividual pharmacokinetic variability, necessitating therapeutic drug monitoring (TDM). Patient-based quality control (PBQC) strategies, such as tracking median drug concentrations, may complement traditional quality assurance in routine laboratory practice. Methods: We retrospectively analyzed 16,495 lamotrigine results collected between 2008 and December 2025 at Uppsala University Hospital, Uppsala. Data included age, sex, sampling date, and lamotrigine concentrations. Assays were performed using the Beckman Coulter DxI 9000 until February 2011, the Architect platform until January 2021, after which the Cobas Pro c 503 platform was implemented. Yearly patient medians were calculated, and trends, seasonal variation, and method agreement were assessed. Results: Of all results, 6,164 were from males and 10,331 from females. Median concentrations were slightly higher in males (15.20 µmol/L) than in females (13.71 µmol/L), representing a weak but statistically significant difference (Spearman R = -0.048; p < 0.0001). The total number of reported results increased steadily over time, from 60 in 2008 to more than 1,500 annually by 2024–2025. Median lamotrigine concentrations increased from 11.65 µmol/L in 2008 to 17.40 µmol/L in 2025 (Spearman R = 0.047; p < 0.0001). Seasonal variation in sample volume was observed, with peaks in November and troughs in July and December, but median concentrations remained stable (CV = 3.15%). Method comparison showed strong agreement between Architect and Cobas assays (R² = 0.97). Conclusions: Patient median lamotrigine concentrations serve as a robust PBQC tool, capable of detecting subtle analytical shifts while remaining resilient to seasonal fluctuations and platform transitions. This approach enhances confidence in assay reliability and supports safer therapeutic decision-making in real-world TDM practice.
