The use of the laboratory

Published on 01/03/2015 by admin

Last modified 01/03/2015

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The use of the laboratory

Every biochemistry analysis should attempt to answer a question that the clinician has posed about the patient. Obtaining the correct answers can often seem to be fraught with difficulty.

Specimen collection

In order to carry out biochemical analyses, it is necessary that the laboratory be provided with both the correct specimen for the requested test, and also information that will ensure that the right test is carried out and the result returned to the requesting clinician with the minimum of delay. As much detail as possible should be included on the request form to help both laboratory staff and the clinician in the interpretation of results. This information can be very valuable when assessing a patient’s progress over a period, or reassessing a diagnosis. Patient identification must be correct, and the request form should include some indication of the suspected pathology. The requested analyses should be clearly indicated. Request forms differ in design. Clinical biochemistry forms in Europe are conventionally coloured green.

A variety of specimens are used in biochemical analysis and these are shown in Table 2.1.

If blood is collected into a plain tube and allowed to clot, after centrifugation a serum specimen is obtained (Fig 2.1). For many biochemical analyses this will be the specimen recommended. In other cases, especially when the analyte in question is unstable and speed is necessary to obtain a specimen that can be frozen quickly, the blood is collected into a tube containing an anticoagulant such as heparin. When centrifuged, the supernatant is called plasma, which is almost identical to the cell-free fraction of blood but contains the anticoagulant as well.