Which additive and tube type is commonly used for a complete blood count (CBC)?

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Multiple Choice

Which additive and tube type is commonly used for a complete blood count (CBC)?

For a complete blood count, you need blood that stays liquid and keeps the cells intact without clumping or changing size. An EDTA-containing additive does exactly that by binding calcium, which stops the clotting process and preserves cell morphology. That makes EDTA in a purple (lavender) top tube the standard choice for CBC specimens. With this additive, red blood cells, white blood cells, and platelets remain in their natural state long enough for accurate counting and analysis. Other tubes are designed for different purposes. Citrate (light blue) is used for coagulation studies because it also chelates calcium but in a way that’s useful for measuring clotting times, not for preserving the cells for a CBC. Clot activator serum tubes (gold SST) are meant to let blood clot and then provide serum for chemistry or serology tests, which removes the cells from the mix and isn’t suitable for CBC. Heparin (green) yields plasma for certain chemistry tests, but it can affect some cell measurements and isn’t the preferred medium for standard CBC analysis.

For a complete blood count, you need blood that stays liquid and keeps the cells intact without clumping or changing size. An EDTA-containing additive does exactly that by binding calcium, which stops the clotting process and preserves cell morphology. That makes EDTA in a purple (lavender) top tube the standard choice for CBC specimens. With this additive, red blood cells, white blood cells, and platelets remain in their natural state long enough for accurate counting and analysis.

Other tubes are designed for different purposes. Citrate (light blue) is used for coagulation studies because it also chelates calcium but in a way that’s useful for measuring clotting times, not for preserving the cells for a CBC. Clot activator serum tubes (gold SST) are meant to let blood clot and then provide serum for chemistry or serology tests, which removes the cells from the mix and isn’t suitable for CBC. Heparin (green) yields plasma for certain chemistry tests, but it can affect some cell measurements and isn’t the preferred medium for standard CBC analysis.

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