The left shift in the arneth index indicates
**Core Concept**
The Arneth index is a measure of polymorphonuclear leukocyte (PMN) neutrophil morphology, specifically the proportion of PMNs with 3, 4, 5, or 6 lobes of cytoplasm. It is a reflection of the body's response to stress, infection, or inflammation.
**Why the Correct Answer is Right**
A left shift in the Arneth index indicates an increase in the proportion of PMNs with 5 or 6 lobes of cytoplasm, which is often seen in conditions of infection or inflammation. This is because the bone marrow responds to the increased demand for PMNs by releasing more immature forms, which have more lobes of cytoplasm. The increased presence of these immature PMNs is a sign of the body's attempt to fight off an infection or inflammation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because a right shift in the Arneth index indicates a decrease in the proportion of PMNs with 5 or 6 lobes of cytoplasm, often seen in conditions of bone marrow depression or severe infection.
* **Option B:** This is incorrect because the Arneth index is not a measure of platelet morphology.
* **Option C:** This is incorrect because the Dohle bodies are a feature of bacterial infection, but they are not directly related to the Arneth index.
**Clinical Pearl / High-Yield Fact**
Remember that a left shift in the Arneth index is a sign of increased bone marrow activity in response to infection or inflammation, and it is often seen in conditions such as sepsis, meningitis, or pneumonia.
**Correct Answer: B. A decrease in the proportion of immature forms (bands) of PMNs.**