What does a blood test look like for a bacterial infection?

Blood routine findings in bacterial infections generally include elevated total white blood cell count, increased neutrophil percentage, elevated neutrophil count, left shift in the nucleus, and elevated C-reactive protein (CRP). Specific details are as follows:

1. Elevated total white blood cell count: During bacterial infection, bone marrow hematopoietic function is enhanced, leading to increased production of white blood cells, with the total count often exceeding the upper limit of the normal range. In severe or systemic infections, white blood cell counts may rise significantly, even resulting in a leukemoid reaction.

2. Increased neutrophil percentage: Neutrophils are the primary cells responsible for defending against bacterial infections. During infection, their proportion often exceeds 70%, and in some patients may reach over 90%. The degree of increase correlates with the severity of infection; mild infections may cause only a slight elevation.

3. Elevated neutrophil count: In addition to increased percentage, the absolute neutrophil count frequently exceeds normal values, potentially surpassing 20×10⁹/L in severe infections. Persistent elevation or recurrent increases suggest uncontrolled infection or the presence of complications.

4. Left shift phenomenon: An increased proportion of immature neutrophils, including more band forms and even late myelocytes or metamyelocytes, indicates accelerated release from the bone marrow. This typically suggests an acute phase of infection or worsening condition, necessitating intensified anti-infective treatment.

5. Elevated C-reactive protein: Although not a direct component of the routine blood test, CRP is commonly measured simultaneously. In bacterial infections, CRP levels rise rapidly, peaking within 48 hours. The magnitude of elevation correlates positively with infection severity, and a subsequent decline indicates favorable treatment response.

Seek timely medical attention when symptoms such as fever or cough occur, and complete necessary tests including blood routine and other relevant examinations. Follow medical advice when using antimicrobial agents, avoiding self-discontinuation or antibiotic misuse. Regularly repeat blood tests during treatment to monitor infection control, and ensure adequate rest and nutritional support.