What does plasma refer to in terms of blood sample composition?

Plasma refers to the liquid portion of blood that contains various substances, including water, electrolytes, proteins, hormones, and waste products, while it is still in the presence of an anticoagulant. Anticoagulants are substances that prevent blood from clotting and are often used in laboratory settings when preparing blood samples for various tests. The presence of an anticoagulant ensures that the blood cells do not aggregate and form clots, allowing for the accurate analysis of the plasma's composition.

This is different from the other choices, which pertain to different states of blood. The liquid portion after clotting and without the anticoagulant would lead to serum, not plasma. The solid portion of blood refers to the components like red blood cells, white blood cells, and platelets. Blood that has clotted would also not contain plasma as it primarily represents the fibrin clot and the formed elements that are no longer in a fluid state. Understanding this distinction is crucial for proper blood sampling and analysis in clinical settings.