Criteria used for screening tests should apply to monitoring

We all want our treatments to work, and none of us wishes treatment to cause harm. Monitoring drug treatment is one way of seeing that a treatment works, while protecting the patient from adverse drug effects. For many patients and many treatments clinical evaluation is sufficient. An example is measuring the blood pressure in a patient on antihypertensive treatment. When therapeutic goals cannot always be directly observed, monitoring may require blood tests in order to know whether they have been reached. An obvious example is the measurement of the international normalised ratio (INR) in patients treated with warfarin. As well as ensuring that the therapeutic goal, the prevention of thrombosis, is likely to be met,1 measuring the INR helps to avoid the risk of haemorrhage, which rises steeply as the INR increases above 2.0.2

Monitoring treatment to anticipate or detect adverse reactions to drugs before they become inevitable or irreversible is clearly important. Upwards of half of the entries in the electronic Medicines Compendium (eMC) suggest monitoring of one kind or another.3 However, for a monitoring test for an adverse drug reaction to be useful clinically, it should satisfy …