Researchers at Hokkaido University in Japan have developed a paper-based point-of-care device which can measure lithium levels in a drop of blood. The device could help patients with bipolar disorder to keep track of their blood lithium levels.

Lithium carbonate is used to treat bipolar disorder, but must be administered carefully as the concentration range in which the drug is therapeutically active is close to its toxic range. This means that patients require regular blood tests to make sure that they are not receiving too high a dose of the drug.

At present, these blood tests need large blood samples and expensive equipment to run, and not all testing labs can perform them. To address this, the Japanese researchers have developed an inexpensive paper-based device to detect lithium in the blood, which could be used in a doctor’s office, or even at home by a patient.

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The device requires a small drop of blood and consists of two units. The first acts to draw blood along and separate it into its constituent components, whereby plasma is allowed to progress to the second unit where a color change occurs depending on the concentration of lithium.

By coating a hydrophobic ink onto the high-purity cotton blotting paper the device is made from, the researchers created a surface that readily absorbs the blood but guides it to the areas where it is required, making liquid handling easier for the user.

Once a drop of blood is added to the unit, it takes only a minute for the device to provide a result. A regular digital camera can be used to image the color change, which is then analyzed. So far, the researchers have shown that the test is similar in accuracy when compared with conventional lab equipment.  

“The device provides an alternative method for regularly monitoring lithium ion concentrations when treating bipolar disorder patients,” said Manabu Tokeshi, a researcher involved in the study. “In the future, we hope to develop a smartphone app for the image analysis so patients themselves or non-medical workers can check the lithium ion concentration in the blood.”

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