Some specimen variations can be controlled through proper patient identification, collection, and handling and strict rejection policies. Light, heat, evaporation, and exposure to the atmosphere will change many substances in routine clinical chemistry testing. Examples include the photodegradation of bilirubin by light exposure and the heat lability of enzymes. Exposure of plasma samples to high temperatures can significantly lower potassium concentrations.4
The laboratory or health-care team can be trained to avoid misidentification, hemolysis, atmospheric exposure to light and heat, and evaporation of blood specimens. Accurate patient identification, specimen identification, and sample aliquot identification are necessary from the time of collection until testing is completed and the result is reported. If there is any question as to the integrity or identification of the sample, the laboratory should reject the sample and request that it be recollected. Supervision of policy adherence and periodic training may be necessary in order to implement and maintain laboratory specimen QA.
Specimen collection and handling procedures must be explained to all parties involved in the processing of specimens. It has become increasingly common for nursing personnel, physician assistants, and health-care professionals other than laboratory personnel to collect blood samples. Although laboratory personnel may not be directly involved in the collection of specimens, they are responsible for minimizing preanalytical errors based on acceptance or rejection of the received specimens. Laboratory personnel are also responsible for training other personnel involved in specimen collection and transport and for communicating effectively in order to maintain optimal quality of specimens for laboratory testing. Since prean-alytical errors seem to make up the majority of most laboratory test problems, proper training is an important area to address.5
Some preanalytical problems may or may not be controlled directly by laboratory personnel, but information about such problems should be made available to health-care providers. These problems include patient-related factors such as ambulation, lying down or standing prior to collection, and biological differences, such as time of day, age, gender, and intake of certain foods or herb supplements. Ambulation prior to specimen collection can impact upon total proteins, lipids, and other protein-bound substances. Levels of cortisol and many other hormones vary throughout the day, so collection needs to be timed according to physician orders hemolysis - rupture of erythrocyte cell membranes causing release of intracellular contents so as to provide the most accurate information. Intake of food greatly impacts on glucose, triglycerides, certain hormones, and electrolytes, so length of fasting prior to specimen collection is a preanalytical factor that is commonly addressed prior to specimen collection and testing.6 Intake of certain foods or herbs may impact on therapeutic drug testing or other laboratory results but often is not within the control of laboratory personnel prior to specimen collection.7 The age of the patient may be an important variable for the test result. For example, bilirubin and alkaline phosphatase values are different in pediatric patients than in adult populations, so coordinated reference intervals are needed. This variation is addressed through the use of age-appropriate reference ranges, but the information on patient age is often obtained at specimen collection, in the preanalytical phase.
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