Toxicology: Featured Tests

Clinical Toxicology is the measurement and interpretation of concentrations of drugs and other toxic substance in human biological fluids for the purpose of patient care. This testing may be necessary when multiple drug ingestion is involved, as the effects of one drug may mask the clinical signs and symptoms of the effects of other drugs. The laboratory test results provide information to the clinician who can make a clinical diagnosis and provide therapy as needed.

Physician speaking to patient

Valproic Acid

Valproic acid is used as an anticonvulsant to treat certain types of seizures, to prevent migranine headaches, and to treat various psychiatric illnesses such as bipolar disorder and aggression. Drugs that compete for protein-binding sites with Valproic Acid, can increase the concentration of Valproic Acid. Therapeutic drug monitoring is useful to optimize dose. Measurement of the free concentration is useful if toxicity is suspected.


Phenytoin is used singly or in combination with other anticonvulsants to treat grand mal epilepsy. Monitoring the serum levels of antiepileptic drugs has increased the efficiency and safety of drug therapy in epilepsy. It facilitates individualization of dosage regimen, reveals irregular drug intake and identifies the responsible agent in intoxicated patients on multiple drug therapy. Free phenytoin is especially useful in patients with altered phenytoin binding to protein, e.g., uremia or individuals having abnormally low levels of albumin, such as nephrotic syndrome. Free phenytoin in serum correlates better with the various other free compartments of the body than does the total drug and is probably a better estimate of the "active drug level" at the receptor site and agrees more with the clinical response.


Carbamazepine is an anticonvulsant which is structurally related to the tricyclic antidepressants and is useful in treating patients with temporal lobe epilepsy. Carbamazepine levels are monitored to assure adequate therapeutic levels are achieved and to avoid toxicity.

Heavy Metals

Excessive exposure to Heavy Metals can cause acute and chronic toxicity.  Heavy metal testing is intended to evaluate and monitor exposure to heavy metals and evaluate the process of detoxification. Quest Diagnostics offers interpretation guides for comprehensive toxic metal panels, peripheral neuropathy testing, cobalt monitoring, thallium toxicity, and test information for the available tests.     


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