Specimen requirement

Adult patient:

  Clotted blood tube (Serum gel separator clot activator tube)

Minimum blood volume: 5 mL

Paediatric patient:

Paediatric clotted blood tube

Number of vials: 1

Minimum blood volume: 0.8 mL

Authorisation code required

No

24 Hr available service

No

For suspected lithium overdose cases, please call Duty Biochemist for 'Urgent' lithium level testing.

Precaution

For monitoring of lithium therapy, blood should be drawn 8 - 12 hours after the last dose.

Method

Ion selective electrode

Reference interval

(Source: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics 4th ed. 2005)

Clinical indication

Therapeutic drug monitoring

Result interpretation

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

When levels are > 1.5 mmol/L, lithium therapy should be discontinued and the patient assessed for toxic symptoms. Symptoms of lithium intoxication include: sluggishness, drowsiness, muscle weakness, and ataxia.

Lithium level > 1.2 mmol/L may be toxic in older patients.

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

Measurement of uncertainty

See table.

If the Na⁺ result is above 169.5 mmol/L or below 89.6 mmol/L for blood / serum, the Li⁺ value cannot be derived. Evaluation study (dated 15 July 2009) showed that the AVL 9181 lithium electrode response became plateau at sodium concentration 160 mmol/L. The lithium electrode shows a slight sensitivity to the ionised calcium present in the sample and results in a negative bias of the lithium result. At normal physiological ionised calcium concentrations, the influence of ionised calcium is clinically insignificant.

Frequency of measurement

Daily