# A nurse is reviewing laboratory results for a postoperative patient. Which value would be most indicative of the patient's overall immune system status?

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> subject: Adult Health

## 문제

A nurse is reviewing laboratory results for a postoperative patient. Which value would be most indicative of the patient's overall immune system status?

## 보기

1. Hemoglobin level of 12.5 g/dL
2. Platelet count of 250,000/μL
3. White blood cell count **✔ 정답**
4. Red blood cell count of 4.2 million/μL

**정답: 3**

## 해설

White blood cell count is the primary indicator of immune function as WBCs are key cellular components. Other options (hemoglobin, platelet, RBC count) assess different systems like oxygen transport or clotting, not overall immune status.

## 심화 해설

Understanding the Question

This question asks you to identify the single best laboratory value that reflects a patient's overall immune system status in a postoperative setting. While multiple lab values provide important clinical information, only one directly measures the cellular component of the immune system.

Analysis of Options

Hemoglobin (Option 1) and Red Blood Cell count (Option 4) are critical for assessing oxygen-carrying capacity and anemia. They do not directly quantify immune function. Platelet count (Option 2) is essential for evaluating clotting ability and bleeding risk. Although platelets play a secondary role in inflammation, their primary function is hemostasis, not representing the body's core immune defense against infection.

White Blood Cell (WBC) count (Option 3) is the most direct and readily available laboratory indicator of immune system status. WBCs, or leukocytes, are the primary effector cells of the immune system, responsible for fighting infection and mediating inflammatory responses. In a postoperative patient, the WBC count is a cornerstone for monitoring for surgical site infection, systemic inflammatory response, or immune suppression.

Deep Dive: The Postoperative Immune Response

The surgical stress response triggers a complex cascade of neuroendocrine, metabolic, and immunological changes. A key feature of this response is the activation of the immune system, which can initially manifest as a leukocytosis (elevated WBC count) due to the release of inflammatory mediators and stress hormones like cortisol [3]. However, this is often followed by a period of relative immune suppression. This postoperative immunosuppression is a significant clinical concern because it can impair wound healing and increase the patient's vulnerability to nosocomial infections [4].

Monitoring the WBC count, along with its differential, allows the nurse to interpret the patient's immune trajectory. A persistently elevated or sharply rising WBC count may signal an infectious complication. Conversely, a critically low WBC count (leukopenia) can indicate overwhelming sepsis or significant immune compromise, which is equally dangerous. The Prognostic Nutritional Index (PNI), a tool used to predict postoperative complications, directly incorporates the total lymphocyte count, a subset of the total WBC count, as a key marker of immune competence, further underscoring the link between these circulating white cells and clinical outcomes [1,2].

Therefore, while a complete blood count (CBC) with differential provides a more detailed picture, the total WBC count is the single value from the options provided that is most indicative of the body's overall immune surveillance and response capability.References (research sources)

- [3]Surgical Stress Response: A Physiological Review of the Endocrine, Immune, and Metabolic Changes.Research articleAcharya K, Rout DK, Kapadia NA, Caroicar YS, Karunakaran NB, Patel P, Thaker H. (2025) · DOI: 10.7759/cureus.100101

- [4]Propofol-based versus volatile anesthesia and postoperative immune response in prostate cancer.Research articleWu Y, Feng D, Xu X. (2026) · DOI: 10.21037/tau-2026-1-0096

## 임상 시나리오

Postoperative Immune MonitoringUsing WBC Count to Detect Infection and Stress Response
The White Blood Cell (WBC) count is the most direct routine lab measure of immune status. After surgery, a physiological stress leukocytosis is common, with levels typically rising to 12,000–15,000/μL within hours and returning to normal in days.

A persistent rise or a dramatic spike above 20,000/μL is highly suspicious for infection (e.g., surgical site infection, pneumonia). A drop below normal (4,000/μL) can signal immune suppression or overwhelming sepsis.

CautionAlways interpret the WBC count with a differential. A "left shift" (increased bands/immature neutrophils) strongly indicates an acute bacterial infection, even if the total WBC count is normal. Never rely on WBC alone; correlate with vital signs (fever, tachycardia) and physical assessment.

## 핵심 개념

- **Leukocytosis** — An increase in the number of white blood cells in the blood, often a sign of infection, inflammation, or a physiological stress response such as surgery.
- **Leukopenia** — A decrease in the number of white blood cells, which can indicate immune suppression, severe infection, or bone marrow dysfunction.
- **White Blood Cell (WBC) Count** — A laboratory test that measures the total number of leukocytes in a volume of blood, serving as a key indicator of immune system activity.
- **Complete Blood Count (CBC) with Differential** — A comprehensive blood test that quantifies WBCs, RBCs, and platelets, with the differential providing a breakdown of specific WBC types (neutrophils, lymphocytes, etc.).

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