Barbiturates - plasma or serum

Last updated: Thursday, 08, April, 2004

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Item Process

5 mL blood in lithium heparin or plain tube.



Spectrophotometry is unsuitable as it does not identify specific barbiturates.

Therapeutic Interval

Definition of the toxic level depends on the type of barbiturate administered.


Assessment of barbiturate overdose.
See Phenobarbitone - serum for therapeutic monitoring. 

In patients with severe head injury thiopentone assay is occasionally required to differentiate reversible CNS depression due to administered thiopentone from brain death.


Depends on the barbiturate identified and the time since ingestion or administration. 

Brain death cannot be reliably diagnosed if a significant level of thiopentone is still present.


Porter WH and Moyer TP. In: Burtis CA and Ashwood ER eds. Tietz Textbook of Clinical Chemistry. 2nd ed. WB Saunders 1994.