Prealbumin is a protein produced primarily by the liver, playing a role in transporting thyroid hormones and vitamin A throughout the body. It is a sensitive indicator used in medical diagnostics, mainly for assessing nutritional status and liver function. Because prealbumin has a short half-life, it responds quickly to changes in nutrition and inflammation, making it valuable for monitoring short-term physiological changes. Obtaining accurate test results depends significantly on proper blood sample collection and handling.
Identifying the Correct Prealbumin Tube
For prealbumin testing, the most commonly recommended blood collection tubes are those designed to yield serum. These often include a serum separator tube (SST), which typically has a gold or “tiger top” stopper, or a plain red top tube, which contains no additives. While serum is generally preferred, some laboratories may also accept plasma samples for prealbumin analysis.
When plasma is required, a green top tube containing lithium heparin is typically used. It is important to consult specific laboratory guidelines, as tube preferences can vary.
Understanding the Tube’s Additive
The specific additives within blood collection tubes facilitate the preparation of the sample for accurate prealbumin measurement. Serum separator tubes (gold or tiger top) contain two primary components: a clot activator and a thixotropic gel barrier. The clot activator promotes rapid blood coagulation, which is necessary to separate the serum from the cellular components of the blood. Following clotting, the gel barrier forms a stable physical separation between the denser blood cells and the lighter serum after centrifugation.
Plain red top tubes, in contrast, contain no additives. Blood collected in these tubes clots naturally without chemical acceleration, also yielding serum. When plasma is needed, green top tubes contain an anticoagulant, most commonly lithium heparin. Heparin prevents blood from clotting by inhibiting thrombin, an enzyme essential for clot formation. This allows the cellular components to be separated from the plasma after centrifugation, providing a liquid sample that retains its original protein composition.
Ensuring Accurate Prealbumin Sample Collection
After blood collection, proper handling steps are important to preserve sample integrity and prevent analytical errors. For serum tubes, the sample must be allowed to clot completely, typically for 30 minutes at room temperature, before centrifugation. Tubes containing additives, such as serum separator tubes or lithium heparin tubes, require gentle inversion, usually 5 to 8 times, immediately after collection to ensure proper mixing.
Centrifugation should occur promptly, ideally within two hours of collection, to separate the serum or plasma from the blood cells. Common centrifugation parameters range from 1200-3000 x g for 5 to 15 minutes, depending on the centrifuge and tube type. After centrifugation, the separated serum or plasma should be transferred into a separate transport tube if not already in an SST, especially if immediate testing is not possible.
For transport and short-term storage, refrigerated temperatures (2-8°C) are recommended, with samples remaining stable for up to 7 to 14 days. For longer storage, freezing the sample at -20°C or colder is advised, but multiple freeze-thaw cycles should be avoided to prevent degradation. Several factors can affect prealbumin levels or interfere with testing, including hemolysis (rupture of red blood cells), lipemia (excessive fats in the blood), and improper storage temperatures. Avoiding vigorous mixing, prolonged tourniquet application, and extreme temperatures during collection and handling helps prevent these issues.