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Best Tests March 2007

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Biochemical Monitoring of Lithium Therapy

Recently in ‘Best Practice Journal’ we provided an overview and guidance on the management of patients taking lithium. Reproduced below is an edited version of laboratory tests usually recommended for the routine monitoring of a patients on lithium. For the full text visit www.bpac.org.nz/magazine/2007/february/lithium.asp

  Routine maintenance Comments
Lithium levels 3-monthly Monitor more frequently in high risk patients, e.g. those on potentially interacting drugs, poor compliance, elderly, unstable renal function, physical illness
Thyroid Function TSH 3 months after initiation and then 6-monthly T4 not routinely required. Monitor for symptoms of hypothyroidism
Electrolytes Check with lithium serum levels every 3 months Particularly important to monitor sodium as it competes for reabsorption in proximal renal tubule
Renal function Check at same time as lithium levels, at least every 3 months Estimate renal function using the Cockcroft and Gault Equation* based on ideal body weight
Serum calcium and magnesium Check every 2 years Lithium may rarely cause hypercalcaemia and hypermagnesium
Parathyroid Hormone (PTH)   Measure only if serum calcium is elevated. PTH must be interpreted relative to serum calcium measurement on the same specimen
*The bpac creatine clearance calculator is based on the Cockroft-Gault equation

Reference: bpacnz. Lithium in General Practice. BPJ 2007;3:16–27.