Determination of plasma and erythrocyte lithium concentrations by atomic absorption spectrophotometry

We describe a method for determining plasma and erythrocyte lithium concentrations by atomic absorption spectrophotometry. Plasma and hemolyzed whole-blood are diluted and analyzed, with use of a lithium hollow-cathode lamp, at 670.8 nm. Erythrocyte lithium concentrations are calculated indirectly from the hematocrit. The standard deviation for a 0.43 mmol/liter pool of whole blood, run daily over 11 months, was +/-20 mumol/liter (CV=5.1). The lithium concentration of a lyophilized pool assayed periodically over the same period (n=127) was 1.84+/-0.05 mmol/liter (CV=2.7%). The relatively low erythrocyte/plasma lithium ratio and the microhematocrit centrifugation force (9600 to 13 600 X g) make corrections for trapped plasma insignificant. Problems with matrix matching and viscosity are overcome by using a plasma pool standard for calculations. Values for erythrocyte lithium concentrations were unchanged in samples stored at room temperature up to 24 h. Hemolysis appears to be of possible clinical significance. This method is useful as a routine clinical laboratory procedure for monitoring patients with affective disorders, who are undergoing therapy with lithium.

Determination of plasma and erythrocyte lithium concentrations by atomic absorption spectrophotometry

We describe a method for determining plasma and erythrocyte lithium concentrations by atomic absorption spectrophotometry. Plasma and hemolyzed whole-blood are diluted and analyzed, with use of a lithium hollow-cathode lamp, at 670.8 nm. Erythrocyte lithium concentrations are calculated indirectly from the hematocrit. The standard deviation for a 0.43 mmol/liter pool of whole blood, run daily over 11 months, was +/-20 mumol/liter (CV=5.1). The lithium concentration of a lyophilized pool assayed periodically over the same period (n=127) was 1.84+/-0.05 mmol/liter (CV=2.7%). The relatively low erythrocyte/plasma lithium ratio and the microhematocrit centrifugation force (9600 to 13 600 X g) make corrections for trapped plasma insignificant. Problems with matrix matching and viscosity are overcome by using a plasma pool standard for calculations. Values for erythrocyte lithium concentrations were unchanged in samples stored at room temperature up to 24 h. Hemolysis appears to be of possible clinical significance. This method is useful as a routine clinical laboratory procedure for monitoring patients with affective disorders, who are undergoing therapy with lithium.

Plasma and erythrocyte kinetic considerations in lithium therapy

Developments in the analysis and pharmacokinetics of lithium, and the role of the pharmacist in the management of lithium therapy in affective disorders, are described. Research showing that lithium levels in the brain may be better predicted from erythrocyte lithium levels than plasma levels is reviewed. Also reviewed is lithium kinetics in affective disorders. The pharmacist (1) determines relevant aspects of the patient's condition, (2) develops an appropriate blood sampling schedule, (3) initiates and maintains a serial lithium erythrocyte and plasma patient profile, (4) evaluates erythrocyte and serum levels in relation to established criteria to provide a basis for differential diagnosis of the patient, and (5) individualizes lithium dosage and schedules. Four cases are used to illustrate this approach. It is suggested that outpatient mental health clinics would be likely settings for the further development of this clinical role.