For electronic requests on EPR, search for the drug name and choose the appropriate blood test. Please give the information requested and time of sample collection in both instances.
Please take samples at the time suggested. Drug levels at other times may give misleading information. For most drugs a good standard sampling time is at trough. Sampling should always be done at the same time during the dosage interval, otherwise comparison of results cannot be made. If toxicity is suspected, do not hesitate to draw blood for analysis, but unless taken at the correct time lithium and digoxin levels must be interpreted with care.
The earliest time a drug level should be measured after initiation of treatment or dosage change. This should allow a steady state level to be achieved. Please see table below.
Treat the patient, not the drug level. Drug interactions are widespread, so knowledge of all the patient's medication is important. Individual drug pharmacokinetics may be influenced by many factors so the same result may mean different things for different patients.
Unless otherwise informed interpretation of results assumes full compliance.
Target ranges refer to monotherapy in adults.
Please note that rarely analytical and biological interference in the methods can occur. An example is digoxin-like immunoreactive substances (DLIS) which can cause a falsely elevated digoxin result. DLIS have been identified in blood from patients in renal failure, liver failure, and pregnant women in their third trimester.
If you require further information about interferences or drug interpretation please contact Clinical Biochemistry 0118 322 7706 / 7704
Additional advice is available from the pharmacies of RBH and Prospect Park hospitals.
Drug | Sampling Time | Resampling Time | Target Range |
Carbamazepine | Pre-dose | 4 days | 4 -12mgl/L |
Digoxin | 6 – 24 hr post dose | 9 days | 0.8 - 2.0 mg/l Heart failure: 0.5 - 1.0µg/L AF: 1.0 - 2.0µg/L |
Lithium | 12hr post evening dose. | 5 days | 0.4 - 0.8mmol/L (locally recommended) |
Phenobarbital | Not critical | 25 days | Adult: 0 - 40 mg/L Neonatal: 0 - 30 mg/L |
Phenytoin | Morning after evening dose | 7 days | Up to 20mg/L (best 10 - 20mgl/L) |
Theophylline | 4 – 6hr post dose | 2 days | 10 - 20mg/L |
Other drugs assays are referred, please supply blood in EDTA vials for immunosuppressives; Ciclosporin, Tacrolimus, Sirolimus, Mycophenolate and plain red top vials for other drugs.
Ethanol, lithium, salicylate, paracetamol and theophylline are available as part of the 24hr Clinical Biochemistry repertoire. Carbamazepine, digoxin and phenytoin are available every normal working day and can be requested out of hours if required urgently.
If a drug screen is needed to identify any unknown compounds taken, the samples are referred to Sandwell and West Birmingham Hospitals NHS Trust. The results are qualitative and are normally issued for clinical use only. Samples should be collected ASAP after suspected poisoning
If there are likely to be any legal consequences, please use the chain of custody requirements.
When making requests for drug screening please:
Turn round time is variable from 2 days up to 5 working days depending on the tests required.