Measurement of Lithium in Saliva
The use of lithium carbonate for the treatment of bipolar disorders and depression is well established.
However, for the treatment to be effective, it must be managed closely, to ensure the dose is maintained within the normal therapeutic range.
The serum level is normally monitored by obtaining blood samples drawn every 48 hours during initial week of treatment. A comparative study of measurement of lithium concentrations in serum and saliva samples shows a very high correlation (r = +0.88).
Estimation of lithium in saliva at different periods of time also shows a good degree of stability.
Based upon this study, monitoring the lithium level in saliva is a viable alternative to serum measurement in the management of patient lithium levels.
6.25% trichloroacetic acid solution is first prepared. To do this accurately weigh out 6.25g of trichloroacetic acid and add it to a 100ml volumetric flask, then make up to the mark with deionized or milliq water.
Calibration standards of 1ppm Li, 5ppm Li and 10ppm Li are available for purchase and cover the expected range of results.
A 5ml sample of patient’s saliva is obtained and thoroughly mixed. A 0.5ml aliquot of the saliva sample is added to 2.5ml of 6.25% trichloroacetic acid. The solutions is thoroughly mixed and analyzed directly without further dilution.
It could be considered matching the matrix of saliva as a blank solution when calibrating to reduce chemical interference between other ions which are present in saliva when preparing calibration standards.
Preparation of Standard Graph
Set the flame photometer in accordance to MultiPoint/Single Ion Calibration found on page 24 of the BWB Technologies Installation and Operation Manual, to measure potassium emission. Nebulize the lithium working standard solutions and adjust the controls until steady zero and maximum readings are obtained. Nebulize the intermediate working standard solutions and construct a graph relating raw emission data (known as RAW in BWB the flame photometer) to concentration of all the standard solutions.