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Question 314
Physiology → Haematology
Classification
Question
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A sample of blood is allowed to clot before the liquid component is separated. Which description best distinguishes the resulting serum from plasma?
Question Stem
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Options
A
Serum contains erythrocytes but plasma does not
B
Serum contains platelets but plasma does not
C
Serum is plasma without clotting factors
D
Serum contains more clotting factors than plasma
E
Serum is the buffy coat after centrifugation
Explanation
Blood consists of formed elements suspended in plasma. distinguishes serum from plasma by stating that serum is plasma without the clotting factors.
Option Validity
A) Erythrocytes are formed elements of blood rather than a defining component of serum. distinguishes serum from plasma according to clotting factors.
B) Platelets are formed elements involved in haemostasis and are not what distinguishes serum from plasma. Serum is defined by removal of clotting factors.
D) This reverses definition. Serum is plasma minus clotting factors rather than plasma with additional clotting factors.
E) The buffy coat contains white blood cells and platelets after centrifugation. It is distinct from serum.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Blood, p.67.