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Therapeutic drug assays

TDL’s therapeutic drug assays measure the serum level of a drug to ensure its concentration is within the therapeutic range.


There are three different collection times for Therapeutic Drug Monitoring:

  • Trough Level: Blood should be collected just before the next dose. Trough Levels check that the appropriate drug concentration is being maintained.
  • Peak Levels: Sample collection time is dependent on specific drug type and method of administration. Peak levels check that the drug level is not in the toxic range.
  • Suspected Toxicity: Blood can be collected any time.


All collections should have the following noted on the request form:

  • Dosage schedule including the amount and frequency and time of the last dose
  • Time of specimen collection
  • Clinical status of patient (e.g. routine, suspected toxicity)
  • Name(s) of other drugs being taken by the patient

Therapeutic drug assay tests

Test codes, sample types, and turn-around times.

Lead consultant

Dr Frank Geoghegan