What is the primary effect of adding 3.2% sodium citrate to a blood sample?

The addition of 3.2% sodium citrate to a blood sample primarily functions to prevent clotting by binding calcium ions. In the coagulation process, calcium plays a critical role as it is essential for various steps in the clotting cascade. When sodium citrate is introduced to the blood sample, it chelates or binds with the calcium, thus removing it from circulation in the sample. Without calcium, the coagulation process is inhibited, and the blood remains in a fluid state, allowing for accurate testing and analysis.

This property of sodium citrate is particularly useful in laboratory settings where anticoagulation is necessary for tests like prothrombin time (PT) or activated partial thromboplastin time (aPTT), which assess the blood's clotting ability. Maintaining the blood in a non-clotting state is crucial for obtaining reliable test results, making sodium citrate a commonly used anticoagulant in laboratory practices.

The other options may relate to different properties of blood samples or the effects of other substances, but they do not directly address the primary function of sodium citrate as effectively as the prevention of clotting through calcium binding.