Clinical toxicology
Hospital toxicology is concerned with individuals admitted to hospital with suspected poisoning and its prime aim is to assist in the treatment of the patient. The range of substances that may be encountered is huge and ideally the hospital laboratory will have the capability to identify and, if required, quantify pharmaceutical agents, illicit drugs, gases, solvents, pesticides, toxic metals and a host of other industrial and environmental poisons in biological fluids. In practice, few laboratories can offer such a comprehensive menu and resources are concentrated on those compounds most often involved in poisoning and for which toxicological investigations are particularly useful to the clinical services. In developed countries, hospital clinical chemistry laboratories are geared to provide these basic services and rely on support from central specialized toxicology laboratories for the rarer cases. Fortunately, in the vast majority of cases the diagnosis can be made on circumstantial and clinical evidence; there is no need for urgent analyses and the analyses can be carried out as a routine exercise. However, when the patient’s condition is severe and the diagnosis is not clear, toxicological tests may be crucial and the analytical results must be furnished quickly (usually within 1 to 2 hours of the patient’s arrival) if they are to have any bearing on diagnosis and treatment. Ideally, the toxic substance can be both identified and quantified within this time frame. When this is not possible, a qualitative result still has considerable value if the symptoms are consistent with the identified toxin and should be relayed to the clinician without delay.
These time constraints entail an inevitable compromise between speed and analytical accu racy and precision. Consequently, the quantita tive methods used may fall short of the standards required, for example, for pharmaco kinetic investigations. However, they must be of sufficient quality to allow an appropriate clinical decision to be made. In this area, close liaison between the laboratory personnel and the clini cian who manages the patient is essential and can save hours of fruitless effort. An attempt must be made to obtain as much information about the patient as possible. This should include not only the clinical picture, but also any previous medical history of poisoning, details of drugs or other substances to which the patient may have had access and, in cases of accidental poisoning, substances to which the patient may have been exposed. This sort of dialogue between the clinician and an experienced analytical toxicologist can often yield clues as to what the cause of toxicity might be and therefore suggest which tests should be performed as a priority. Close communication must continue if the initial tests prove negative, so that the search has to be widened, or if the clinician requires advice on the interpretation of positive results. Laboratories that provide analytical toxicology analyses to assist with cases of acute and chronic poisoning often offer additional services in the area of drug abuse. This can range from diagnostic tests to uncover the covert misuse of laxatives and diuretics through to routine screening of urine samples from patients assigned to treatment and rehabilitation programmes. For the latter, the require ment is to establish the drug-taking patterns of new patients and to monitor their subsequent compliance with the prescribed treatment regime. Details of techniques suitable for these services are given in separate sections.
