Basic concepts in clinical testing
Patients can generate a mass of laboratory data, including reports from haematology, biochemistry and microbiology departments. Some of these will be relevant to drug therapy in that test results can call for a dosage adjustment or a change of drug. Patients can also undergo various types of diagnostic scan such as magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound. Community pharmacists are often asked about such tests. Before a test, patients may want to know what the procedure involves and, after a test, they may be worried about the results and what they could mean. Pharmacists can do a great deal to allay such fears by giving clear, confident explanations of tests. An awareness of the tests used to identify early signs of disease (eg, mammography, cervical smear) will also facilitate the role of pharmacists in health promotion.
Pharmacists who work either in hospital or primary care and those with access to patient records, also need to be familiar with test results and what they might mean. Not all laboratory data are of direct relevance to pharmacy, but a general knowledge of these is recommended in order to understand a patient’s medical background and to be able to discuss the care of patients with other health care professionals.
Increasingly, pharmacists are offering diagnostic (“near-patient”) testing in addition to selling a widening range of testing kits for home use. They also, therefore, need to be able to interpret results and advise patients appropriately. This series of articles will explore many of the aspects of clinical testing.
Uses of clinical tests
Clinical tests can be used for several purposes:
- To confirm or support a diagnosis (eg, bone densitometry for suspected osteoporosis, biopsy in suspected coeliac disease and fasting blood glucose in suspected diabetes mellitus)
- To assess the severity of a disease (eg, MRI for the stage of a tumour and measuring creatinine clearance to assess the level of renal impairment)
- To monitor the response to a treatment (eg, serum cholesterol following initiation of lipid-lowering therapy)
- To monitor appropriate drug dosing (eg, international normalised ratios for oral anticoagulants)
- To help prevent toxic side effects and interactions (eg, monitoring serum lithium levels)
Interpretation of test results
Test results can be expressed qualitatively, quantitatively or semi-quantitatively. Results from scans and endoscopic procedures are largely qualitative. They will describe the appearance of the tissue under investigation and will explain the clinical significance of any abnormalities.
Haematology and biochemistry results are generally expressed quantitatively (ie, as a set of numbers) and microbiological results tend to be semi-quantitative in that reports will identify the micro-organisms present and describe their sensitivities to antibiotics.
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Citation: The Pharmaceutical Journal URI: 10997010
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