Lithium

5 mL blood in plain tube; a lithium heparin tube must not be used.

Flame emission spectrophotometry or ISE.

0.6-1.2 mmol/L.

Monitoring lithium therapy, blood should be drawn 8-12 h after the last dose.

Lithium half-life is 8-20 h; may be prolonged in renal failure.

Toxic level: > 1.9 mmol/L (> 1.2 mmol/L may be toxic in older patients).

When levels are > 1.5 mmol/L, lithium therapy should be discontinued and the patient assessed for toxic symptoms.

Increased levels may occur in sodium depletion, eg, associated with diuretics.