Preanalytical variables

In designing studies and before the interpretation of data, it is important to consider some of the variables that can affect the data but are unrelated to the compound being tested because changes can occur in plasma and urine values due to normal biological variations. In addition to biological variations, other variations may be caused by analytical variation and the methodological variation that occurs when a study is performed. 

In this chapter some of the preanalytical factors are considered  

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Preanalytical Variables Affecting Global Coagulation Tests. 157... 

Preanalytical variables that affect global tests for coagulation such as prothrombin time (PT) and activated partial thromboplastin time (APTT) include the choice and concentration of anticoagulant, anticoagulant-to-blQod ratio, pH, concentration of divalent cations, hematocrit, and storage temperature, to mention a few. 

Espina, V. Reduction of preanalytical variability in specimen procurement for molecular profiling... 

Young DS. Effects of preanalytical variables on clinical laboratory tests. 2" edition. Washington DC AACC Press, 1997. 

The human body is composed of many different compounds and elements the concentration or activities of these analytes are a reflection of the individual s health or pathophysiological state. However, both preanalytical variables and biological variation affect the concentration or activities of these analytes. ... 

Preanalytical variables fall under two categories—those that are controllable and those that are not. Those that can be controlled have short-lived effects. Duration of the other factors is much longer. Standardization of specimen collection practices minimizes the variables that cause changes in test values within one day or from one day to another and thereby reduces the difficulty in interpretation of values (see Chapter 2). However, in many healthcare facilities, standardization is not always possible. Thus one must understand the influences of both controllable and uncontrollable variables on the composition of body fluids. 

Many of the preanalytical variables related to specimen collection that were discussed in Chapter 2 are examples of controllable variables. Others include physiological variables and those associated with diet, lifestyle, stimulants, drugs, herbal preparations, and recreational drug ingestion. 

Examples of noncontroUable preanalytical variables include those related to biological, environmental, and long-term cyclical influences and those related to underlying medical conditions. 

Hannon R, EasteU R. Preanalytical variability of biochemical markers of bone turnover. Osteoporos Int 2000 ll S30-44. 

The responsibility for accurate and timely test reports generally lies with the laboratory, but many problems can arise before and after the analysis of the submitted specimens. To monitor and control these errors, it is essential to perform a systems analysis of the laboratory and to identify the types of preanalytical variables. 

Guder W, Narayanan FI, Wisser H, Zawata B. List of analytes preanalytical variables. In Guder W,... 

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