Preanalytical variables control

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. 

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. 

The control of preanalytical conditions or variables, such as test requests, patient preparation, patient identification, specimen acquisition, specimen transport, specimen processing, specimen distribution, preparation of work lists and logs, and maintenance of records (see Chapters 1 and 17). ... 

Changes in the means of patient populations may be caused by multiple variables (see Chapters 16 and 17). Changes in the demographic and clinical characteristics of the patients, such as the ratio of males to females, the ratio of hospitalized patients to outpatients, or the presence of many specimens from a specialty clinic can alter the mean value. Similarly, changes in preanalytical conditions,such as tourniquet time and specimen storage, alter patient population means and can therefore be monitored by use of patient means. These variables are not monitored by those control procedures employing stable materials thus the patient mean procedures provide additional capabilities and should be used in conjunction with other control procedures. 

It has been more than 10 years since the book Animal Clinical Chemistry A Primer for Toxicologists was published by Taylor Francis, and that hook evolved from the contributors to training courses held in the United Kingdom. This hook has similar objectives and designs. Information has been collated from published papers, textbooks, and unpublished data, with references provided at the end of each chapter or in Appendix A, where readers are provided with some key references on published reference ranges for laboratory animals. Two chapters are devoted to preanalytical and analytical variables. These variables play a far more important part when data from animal studies are interpreted compared to data obtained for humans, where many of the variables can be well controlled or have less physiological effect. 

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