Fever: Which Blood Tests to Run and Why

Fever is a common symptom that indicates your body is fighting an infection or illness. It can be caused by a variety of conditions, from minor infections to more serious diseases. Understanding which blood tests can help identify the underlying cause of a fever is important for effective treatment.

What is a fever?

A fever is an increase in body temperature above the normal range, usually considered to be around 98.6°F (37°C). It is a natural response of the body to fight off infections by creating an environment less favorable for bacteria and viruses. While a mild fever is often harmless, a high or persistent fever may require medical attention to determine the underlying cause.

Common blood tests for fever

Complete Blood Count (CBC)

A Complete Blood Count (CBC) is one of the most common blood tests used to evaluate the cause of a fever. This test measures various components of your blood, including white blood cells (WBCs), red blood cells, and platelets. An elevated WBC count can indicate an infection or inflammation, helping to identify whether a bacterial or viral infection might be present.

C-Reactive Protein (CRP) Test

The C-Reactive Protein (CRP) test measures the level of CRP in your blood, a protein produced by the liver in response to inflammation. High levels of CRP can suggest an acute inflammatory condition, which might be causing the fever. It is often used in conjunction with other tests to assess the severity of the inflammation and guide further testing or treatment.

Blood Culture

A blood culture test is used to detect the presence of bacteria or fungi in the blood. This test is particularly important if a systemic infection is suspected, such as sepsis, which can cause high fever. Blood cultures help identify the specific organism causing the infection, allowing for targeted antibiotic treatment.

Erythrocyte Sedimentation Rate (ESR)

The Erythrocyte Sedimentation Rate (ESR) test measures how quickly red blood cells settle at the bottom of a test tube. A faster-than-normal rate may indicate inflammation in the body. While not specific to any particular disease, it can be useful in detecting general inflammation and guiding further diagnostic testing.

When to see a doctor

If your fever is very high, persistent, or accompanied by severe symptoms such as difficulty breathing, confusion, or a rash, it is important to seek medical attention promptly. Additionally, if you have a weakened immune system or underlying health conditions, consult a healthcare provider if you develop a fever.

Frequently asked questions

What is the normal range for body temperature?

The normal body temperature range is typically between 97°F (36.1°C) and 99°F (37.2°C). A fever is generally considered to be a body temperature of 100.4°F (38°C) or higher.

Can stress cause a fever?

While stress itself does not cause a fever, it can weaken your immune system, making you more susceptible to infections that can lead to a fever.

How is a fever treated?

Treatment for a fever depends on its cause. For mild fevers, rest and hydration are often sufficient. If a bacterial infection is suspected, antibiotics may be prescribed. Over-the-counter medications like acetaminophen or ibuprofen can help reduce fever symptoms.

Is a fever always a sign of infection?

Not always. While fever is commonly associated with infections, it can also be caused by other conditions such as autoimmune diseases, heat exhaustion, or certain medications.

What should I do if my child's fever doesn't go down?

If your child's fever persists or is accompanied by symptoms like lethargy, irritability, or a rash, contact a healthcare provider. Children are more vulnerable to the effects of fever, and prompt evaluation is important.

Conclusion

Blood tests are valuable tools in determining the cause of a fever and guiding treatment decisions. Understanding the purpose of each test can help you and your healthcare provider make informed decisions about your health. Always consult with your healthcare provider for personalized advice and treatment options.

Disclaimer: This article is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for any health-related concerns.