ANALYTICAL TOXICOLOGY - INVESTIGATION OF SUSPECTED POISONING

In cases of drug overdosage or occupational poisoning, it is always advisable to contact the Laboratory before the specimens are sent.

There are no simple tests that are able to detect all of the drugs and other poisons that might have been ingested by a patient. Investigations for an "unknown" drug or poison are usually carried out on specimens of urine (30 mL - for qualitative tests) and blood (10 mL - for quantitative tests) and carried out on a 24 hour basis. Stomach aspirate or wash-out liquid are not usually required. The majority of investigations are done on an emergency basis and completed within 1-2 hours. When carrying out these investigations it is vital that the laboratory is fully aware of the patient history, findings from the clinical examination, therapy given and the results of other investigations. A close liaison between the requesting physician and the Laboratory is an important requirement for providing an efficient laboratory service.

Please note:

A special protocol has been developed for the investigation of spiked drinks.

In general, investigations should only be requested if they are likely to aid diagnosis or influence the management of the patient.

Advice on the clinical management of poisoning is available from the West Midlands Poisons Unit at Birmingham City Hospital (0121 507 5588/5589).

Specimen collection

Specimens required for performing laboratory investigations for the detection of an unknown drug or poison:

Urine:

30 mL (Sterilin Container). NO PRESERVATIVE.

NOTE: - DO NOT add any preservative e.g. boric acid.

Blood:

10 mL heparinised (avoid gel-containing tubes if possible).

Small specimen volumes may be accepted for paediatric cases.

 

It is important to write the full name of the patient on each specimen container, also the date and time of collection. It is advisable to collect specimens as soon as possible following admission, prior to treatment. Each request should come with a properly completed request card giving sufficient background information and indicating the nature of the investigation required, also the name and bleep number of the requesting doctor.

Useful Information for the Investigation of Poisoned Patients

1. Patient's occupation and likely access to specific drugs or poisons.

2. Relevant previous medical history e.g. history of depression that may indicate the availability of certain types of medication.

3. Date and time of alleged ingestion in relation to admission to hospital.

4. Drugs previously prescribed to the patient or accessible in the home: this latter point is particularly important in cases of paediatric poisoning.

5. Clinical examination of the patient and specific features such as depth of coma, respiratory depression or failure, epileptic fits, cardiac arrhythmias, cardiovascular status, temperature and any significant neurological features.

6. Ingestion of alcohol. The consumption of large quantities of alcohol may cause deep coma in some cases. It is important to indicate if the patient smells of alcohol or other substances on the breath e.g. acetone, which could suggest other problems e.g. ketoacidosis.

7. Results of any toxicological investigation already carried out by a local laboratory e.g. salicylate, and paracetamol.

8. All drugs given in treatment since admission, including antidotes, antibiotics and anaesthetic agents. [Note: many of these substances will be detected by the screening procedure and if not declared may hinder the interpretation of results].

9. Any medico-legal aspects of the case e.g. suspected Munchausen Syndrome by Proxy.

10. Urgency of requested investigation

Substances screened for in a 'Standard' Qualitative 'UNKNOWN' Drug Screen.