Interpreting lipid values in the laboratory

Useful laboratory interpretation depends on 3 factors: a valid sample, an accurate method and a specific interpretation. A, valid sample may be affected by a number of conditions. For example, precollection conditions are important. Among the circumstances that influence the precollection condition are the patient’s life-style, diet, exercise and medication, especially diuretics. Intercurrent illness can also alter a patient’s lipid levels; e.g., cholesterol levels drop dramaticaily in the weeks after a myocardial infarction. Several factors that influence collection conditions deserve consideration. For example, if a person is recumbent for 20 minutes before a sample is taken, there can be a 15% change in the cholesterol value. If the tourniquet is applied too tightiy for longer than 2 minutes, a change of 2 to 10% in the value can result. In addition, the anticoagulant used in the vacuum container can dramatically affect the sample. Heparin does not cause any difference between plasma or serum; however, versene causes a 3 to 5% difference. Oxalate creates an 8% difference, and citrate and fluoride can cause changes of as much as 12 and 18%, respectively. When using plasma, a full tube should always be collected. The source of the blood also affects the cholesterol level; there are differences between arterial and venous blood. With regard to laboratory conditions, the measurement will be affected by the handling, storage and shipment of the specimen. In addition, the laboratory should have stable material with which to perform its analysis.