Lithium is the first-line treatment for bipolar disorder. However, the narrow therapeutic window of serum (s-)lithium is near its toxicity range, necessitating continuous monitoring of patients, a process involving regular hospital visits. On-demand home sampling could allow for more frequent testing, possibly resulting in safer patient outcomes, further dosage optimization, and increased compliance. This article presents a device that measures the s-lithium concentration from whole blood. The device consists of a single-use cartridge able to conduct on-chip serum filtration, volume-metering and an on-chip colorimetric assay. Spiked whole blood shows good linearity (Pearson's r = 0.96, R2 = 0.92), a limit-of-detection of 0.3 mmol L-1, and an average deviation of 0.05 mmol L-1 (+/- 6%) compared to atomic absorption spectroscopy. The on-chip colorimetric assay has shown to be a promising technique for measuring s-lithium concentration from whole blood and could allow patients to assess lithium levels at home and make the treatment available for new patient groups.

Background: Lithium is a cornerstone in the treatment of bipolar disorder and is considered one of the most effective treatments in psychiatry at large. Lithium treatment requires individual dosing with frequent serum concentration measurements due to the narrow therapeutic window and risk of toxicity. There is need for patient-centric methods for lithium monitoring and the use of dried blood spots has recently been proposed for determination of lithium concentration. The purpose of the current study was to assess feasibility of this method by introducing a volumetric technique developed for home-sampling. Materials and methods: Laboratory: Capillary blood was sampled by finger-prick using a volumetric device that collects 10 mu L volumes as a dried blood spot. Lithium was measured in the dried blood spots using a validated atomic absorption spectroscopy method. Clinical: Thirty-nine lithium-treated patients were recruited, and dried blood spots and venous blood samples were collected. Routine serum analysis was performed for comparison. Results: The range of serum lithium concentrations was 0.41-1.22 mmol/L, and the dried blood spot/serum ratio was 0.78. A strong linear correlation between the two specimens was shown with Pearson's R = 0.95 (r2 = 0.90). Adding hematocrit as a variable only minimally improved prediction. Conclusion: Volumetric dried blood spots is a promising technique for measurement of lithium concentrations. This will enable home-sampling and could potentially save resources, improve compliance, and make treatment safer. This may facilitate the use of lithium treatment in regions where monitoring via venous blood sampling remains difficult. However, the usability of dried blood spots for monitoring lithium treatment longitudinally remains to be examined.