REGIONAL LABORATORY for TOXICOLOGY

Guide to Screening for an Unknown Drug or Poison

1. INTRODUCTION

2. 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. A wide variety of substances may be involved, which include: gases, volatile liquids, inorganic metal salts, pharmaceutical products, illicit drugs, herbicides and pesticides. Patients may also ingest cocktails of substances with or without alcohol. Patients from overseas may have access to pharmaceutical and herbal products that are not commonly available in the U.K. 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 qualitative and quantitative tests) and undertaken on a 24 hour basis. Stomach aspirate may sometimes be useful, as are the contents of bottles or tablet containers – so called "scene residues". Most investigations are done on an emergency basis and completed within 2 hours. The rapid turnaround time is important if investigations are to influence acute patient management. When carrying out these investigations it is of great importance that the laboratory is aware of the patient history, findings from the clinical examination of the patient, and the results of other investigation. A close liaison between the requesting physician and the laboratory is an important requirement for providing an efficient laboratory service. Those clinical situations where toxicological investigations may be useful are listed in Table 1. In general, investigations should be only requested if they are likely to aid diagnosis or influence the management of the patient.

3. SPECIMEN COLLECTION

Specimens required for carrying out 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). Smaller specimen volumes may be accepted for paediatric cases.

Stomach contents: Stomach contents and washout are not normally required for screening purposes, unless they are found to contain intact tablets, capsules or other material that may be easily identified.

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.

3. HOW TO REQUEST A SCREEN

4. Please always contact the laboratory BEFORE sending any specimens and discuss the case with a senior member of the laboratory staff:

   Dr Stephen George, Clinical Toxicology Section Head: 0121 507 6029

   Other senior staff: 0121 507 4135/6

   It is important to establish the full available history on a patient before making a request.

    

4. TRANSPORT AND STORAGE OF SPECIMENS

If there is delay in the transport of specimens to the Laboratory they should be kept at 4°C in a refrigerator. Specimens of blood should be in secure containers and enclosed in individual plastic bags, suitably packed in a rigid box. DO NOT SEND SPECIMENS IN JIFFY BAGS OR USE STAPLES. If investigations are required urgently specimens should be transported to the Laboratory by taxi or appropriate rapid transport. IT IS IMPORTANT TO ALWAYS RING THE LABORATORY BEFORE SENDING URGENT SPECIMENS.

5. IMPORTANCE OF HISTORY WHEN REQUESTING INVESTIGATIONS

	Patient’s occupation and likely access to specific drugs or poisons.
	Relevant previous medical history e.g. psychiatric history or diseases such as epilepsy that may indicate the availability of certain types of medication.
	Date and time of alleged ingestion in relation to admission to hospital.

	Drugs previously prescribed to the patient or accessible in the home; this latter point is particularly important in cases of paediatric poisoning.
	Clinical examination of the patient and specific signs and symptoms of poisoning.
	Ingestion of alcohol. The consumption of very large quantities of alcohol may cause deep coma in some cases. It is useful 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.

	Results of any biochemical or haematological investigations carried out on admission e.g. blood, glucose, electrolytes and gases.
	Results of any toxicological investigations already carried out by a local laboratory e.g. salicylate, paracetamol.
	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).

6. BIOCHEMICAL AND HAEMATOLOGICAL INVESTIGATIONS

7. There are a number of biochemical and haematological that may indicate a diagnosis of poisoning. Many of these changes are non-specific, but may indicate the ingestion of certain agents that can be investigated by the screening procedures.

    

7. SCOPE OF SCREEN

8. It would be impossible to screen for all substances that might have been ingested by a patient. It is always important to discuss the required scope of the investigations when requesting an ‘unknown’ drug screen. The ‘standard’ screening procedure carried out is designed to look for those substances most commonly ingested by patients and likely to cause harm. The screen also seeks to confirm (or refute) the ingestion of substances that the patient is thought to have ingested or had access to.

    

TABLE 1

1.     Assessment of the severity of poisoning (quantitative analyses)
2.     Where a diagnosis of poisoning is uncertain, particularly in children
3.     Differential diagnosis of coma
4.     Where administration of an antidote depends on the rapid identification of a poison and its concentration in          blood
5.     The prognosis of complications or fatal outcome to poisoning
6.     To monitor the efficacy of an active elimination technique or antidote.
7.     Investigation of non-accidental poisoning in children, e.g. "child abuse" or Münchausen’s Syndrome by Proxy.
8.     Confirmation of substance or drug misuse
9.     Investigation of new drugs or an unusual clinical presentation
10.     Investigation of adverse drug reactions and iatrogenic poisoning
11.     The confirmation of brain death
12.     Occupational or environmental exposure to chemicals including chemical accidents

1.     History of Patient
2.     Signs and symptoms of poisoning
3.     Laboratory and other investigations already carried out
4.     Drugs given in treatment since admission (written list)
5.     Will the analysis influence diagnosis or management?
6.     How urgent is the request?
7.     Date and time of ingestion in relation to presentation in hospital
8.     Date of time of specimens in relation to admission
9.     Transport of specimens in Laboratory
10.     Name and bleep number of requesting physician for reporting urgent results
11.     Any medico-legal issues
12.     Scope of the investigations to be carried out

SPECIFIC SUBSTANCES AND GROUPS OF DRUGS AND EXAMPLES OF SPECIFIC SUBSTANCES WHICH MAY BE DETECTED IN URINE*

*Ethanol will also be measured quantitatively provided that a suitable blood or urine specimen is provided.

NOTES:

1. The "turn-around-time" for an urgent "standard" qualitative drug screen is normally 1-2 hours from the receipt of the specimen by the Laboratory. (Please note that surcharges for "within-hours" urgent requests and out-of-hours requests are made).

2. An extended description of the Unknown Drug Screening procedure may be obtained form the laboratory upon request.

3. Minimum sample requirements: 30ml Urine + 10ml Blood (see also the table of Assay Availability & Sample Requirement)

4. More extensive drug/poison screening tests and quantitative analyses may be carried out on individual cases, depending on the history and clinical indications. These additional tests include: cyanide, glycols, diuretics, chlorphenoxy herbicides, laxatives, paraquat, volatile solvents and gases, heavy metals etc.

Last modified: June 16, 2005

Copyright ^© [Regional Laboratory for Toxicology], 2002. All rights reserved.