October 24, 2010

USMLE 2 Question 19

A 13 year old female has swollen cervical lymph nodes and is febrile. Her blood culture is positive for staphylococcus aureus. She shows other signs of being septic. The intern attending her tells her associate that the patient's WBC count is 15,000 cc/mm with a shift to the left.

What does she mean by a 'shift to the left?'

a) increased number of white blood cells in the peripheral blood
b) decreased number of white blood cells in the peripheral blood
c) hypersegmented granulocytes present in the peripheral blood
d) increased number of immature white blood cells in the peripheral blood
e) increased number of immature red blood cells in the peripheral blood







ANSWER
The correct answer is D




Explanation
A shift to the left refers to an increase number of immature white blood cells in the peripheral smear. Typically, the immature white blood cells are being released prematurely by the bone marrow in order to combat some sort of infection.

An increased number of white blood cells in the peripheral blood (choice a) is called a leukocytosis. A decreased number of white blood cells in the peripheral blood (choice b) is called a leukopenia. Hypersegmented granulocytes present in the peripheral blood (choice c) is a shift to the right. An increased number of immature red blood cells in the peripheral blood (choice e) is a reticulocytosis.

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