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Question 296
Physiology → Haematology
Classification
Question
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A patient has marked microcytosis. In the absence of another dominant influence, what effect may this have on the erythrocyte sedimentation rate?
Question Stem
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Options
A
Markedly increases ESR through increased plasma protein
B
Increases ESR because smaller erythrocytes sediment more rapidly
C
Has no effect on ESR
D
Produces an artefactual reduction in ESR
E
Causes ESR to equal the patient's age
Explanation
lists microcytosis as producing an artefactual reduction in ESR. It separately states that ESR tends to increase with larger cells, fewer cells and increased plasma proteins.
Option Validity
A) Microcytosis itself is not described as increasing plasma proteins. Increased plasma proteins are a separate factor associated with increased ESR.
B) The relationship described is the opposite. Larger cells favour an increased ESR, whereas microcytosis may artefactually reduce it.
C) explicitly includes microcytosis among factors capable of reducing ESR. It therefore cannot be regarded as having no effect.
E) gives an approximate age-related relationship for normal ESR, but microcytosis is separately identified as a factor that can artefactually reduce the measured value.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - ESR, p.68.