Approach to a fever: Clinical sciences

Fever is generally defined as a temperature of 100.4 degrees Fahrenheit or 38 Celsius, or higher. It occurs when chemical triggers, called pyrogens, stimulate the thermoregulatory center in the hypothalamus, which in turn elevates the body temperature. Pyrogens can be either endogenous, like cytokines from various inflammatory processes or tumors; or exogenous, like antigens from various pathogens. Now, some important causes of fever to keep in mind include infection, venous thromboembolism, malignancy, autoimmune disease, and certain medications, as well as fever of unknown origin.

Now, if your patient presents with a fever, you should first perform an ABCDE assessment to determine if your patient is unstable or stable. If unstable, stabilize their airway, breathing, and circulation. Next, obtain IV access and start fluid resuscitation as well as broad-spectrum intravenous antibiotics. Place your patient on continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation. Finally, if needed, provide supplemental oxygen!

Okay, let’s jump right back to the ABCDE assessment and take a look at stable patients. In this case, start by obtaining a focused history and physical examination. A body temperature of 100.4 degrees Fahrenheit or 38 degrees Celsius or higher confirms a fever, which could be accompanied by tachycardia. Once you confirm the presence of fever, your next step is to determine the underlying cause by taking a deeper look at history and physical examination for additional clues.

Okay, the first cause of fever to consider is infection! Your patient’s history may include close contact with a sick individual, recent travel, IV substance use, or high-risk sexual activity. They may report symptoms like cough, malaise, chills, muscle or joint pain, painful urination, or decreased appetite, as well as additional symptoms based on the organ system involved.

Additionally, physical exam findings might reveal tachycardia, tachypnea, lymphadenopathy, abnormal breath sounds, a lesion on the genitalia, or a rash, depending on the underlying cause.

At this point, consider infection as a cause of fever, with your next step being to order labs, including a CBC, as well as inflammatory markers like ESR, CRP, and procalcitonin. Keep in mind that lab work-up might be extensive depending on which infection is suspected. For example, if you suspect a bacterial infection, you may need to obtain blood or urine cultures; or if you suspect a viral infection, you might need to obtain a viral serology. Additionally, in some cases, you may consider imaging, like a chest X-ray, CT, or MRI. If confirmatory testing identifies infection, or if you can make a clinical diagnosis based on your findings, diagnose infection as a cause of fever.

Next up is venous thromboembolism. In this case, your patient may have risk factors like age over 65, recent surgery, prolonged immobilization, or active malignancy. Other important risk factors include obesity, smoking, pregnancy, and oral contraceptive use, as well as certain genetic conditions that promote thrombosis. Additionally, your patient may report extremity pain with swelling and warmth in the affected area, suggesting a DVT; or even trouble breathing, sharp chest pain, or hemoptysis that suggests a PE.

In the case of a DVT, your physical exam may reveal an edematous limb with erythema, warmth, and tenderness to palpation. It may also show a palpable thrombotic vein, or a positive Homan sign, characterized by pain in the calf muscles during ankle dorsiflexion. On the flip side, a PE will likely show exam findings such as tachycardia, tachypnea, or wheezing.

With these findings, consider venous thromboembolism as a cause of fever, and obtain a Doppler ultrasound of the affected extremity to evaluate for a DVT; or consider a chest computed tomography angiography to evaluate for a PE. If either reveals a thrombus, diagnose venous thromboembolism as the source of fever!