Preservation of Specimens in Transit

Although delays of a specimen in transit from a patient in a hospital to the laboratory are usually short, the time elapsing from the separation of serum and cells until analysis may be considerable. The specimen must be properly treated both during its transport to the laboratory and from the time the serum has been separated until it is analyzed. For some tests, specimens must be kept at 4 C from the time the blood is drawn mitil the specimens are analyzed, or until the serum or plasma is separated from the cells. Examples are specimens for ammonia and blood gas determinations, such as PCO2, PO2, and blood pH (see Chapter 27). Transfer of these specimens to the laboratory must be done by placing the specimen container in ice water. Specimens for acid phosphatase, lactate and pyruvate, and certain hormone tests (e.g., gastrin and renin activity) should be treated the same way. A notable decrease in pyruvate and increase in lactate concentration occurs within a few minutes at ambient temperature (see Chapter 25). 

For all test constituents that are thermally labile, serum and plasma should be separated from cells in a refrigerated centrifuge. Specimens for bilirubin or carotene and some drugs, such as methotrexate, must be protected from both daylight and fluorescent light to prevent photodegradation. Some special handling requirements are fisted in Table 2-7. 

Although transport of specimens from the patient to the clinical laboratory is often done by messenger, pneumatic tube systems have been used to move the specimens more rapidly over long distances within the hospital. Hemolysis may occur in these systems unless the tubes are completely filled and movement of the blood tubes inside the specimen carrier is prevented. The pneumatic tube system should be designed to eliminate sharp curves and sudden stops of the specimen carriers, because these factors are responsible for much of the hemolysis that may occur. With many systems, however, the plasma hemoglobin concentration may be increased, and the serum activity of red cell enzymes, such as lactate dehydrogenase, may also be increased. Nonethe- 

TABLE 2-7 Selected Blood Constituents Requiring Special Collection and Storage Conditions  

S-Acetone, acetoacetate S-Acid phosphatase P-ACTH (corticotropin) S-Alcohol S-Aldolasc P,S-Aldosterone P-Amino acids S-Androstenedione S-Ascorbic acid S-Barbiturates S-BUe acids 

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