Final answer:
The order of draw for capillary collection is different than venipuncture mainly because of additive cross contamination. Capillary samples are prone to such contamination due to the smaller size and the use of multiple microcollection tubes in a sequence.
Step-by-step explanation:
The order of draw for capillary blood collection differs from venipuncture primarily due to additive cross contamination. Capillary collections typically involve smaller sample sizes, and capillary blood mixes with interstitial and intracellular fluids, which can alter test results if not drawn in the correct order. The risk of hemoconcentration with capillary samples is lesser compared to venous samples because the capillary blood is often used immediately and collected in smaller quantities. Additive cross contamination is of particular concern because the use of multiple microcollection tubes can easily lead to the transfer of additives between tubes if not ordered properly.
Hemoconcentration can occur during venipuncture due to the use of a tourniquet, which is not applicable in capillary collections. The increased rate of coagulation in capillary blood can also affect the order of draw but is not the primary determining factor. As capillaries are the site of capillary action, which draws blood into a small diameter glass tube, maintaining the integrity of the sample by following the correct order of draw minimizes pre-analytical errors and ensures diagnostic accuracy.