SYMPTOMS

What is low-grade fever?

The normal body temperature of a healthy person is generally around 36°C to 37°C, with slight variations depending on the measurement method. For example, the normal range for sublingual temperature is 36.3°C to 37.2°C, for rectal temperature it is 36.5°C to 37.7°C, and for axillary (armpit) temperature, it is 36°C to 37°C^[1].

Low-grade fever refers to an axillary temperature higher than the normal range but not exceeding 38°C^[1].

Is human body temperature constant?

The body temperature of a healthy person fluctuates slightly, typically being higher in the afternoon than in the morning. It may also rise slightly after intense exercise or eating, but the overall fluctuation does not exceed 1°C.

This is mainly due to the body's thermoregulatory center in the brain, which functions like an "air conditioner." When body temperature rises too high, it takes measures to lower it, maintaining it within the normal range, and vice versa.

When the thermoregulatory center is impaired due to various pathogenic factors, this "air conditioner" fails to function properly, leading to body temperatures exceeding the normal range and resulting in low-grade fever, high fever, or even hyperpyrexia.

Additionally, low-grade fever can occur under physiological conditions, such as before menstruation or during early pregnancy in women, due to stress, after intense exercise, or in hot environments.

How long does low-grade fever usually last?

Low-grade fever may persist until the underlying cause is resolved, gradually returning to normal. It can also recur cyclically, lasting for hours, days, or even years.

What are the types of low-grade fever?

• Primary low-grade fever: Caused by dysfunction of the thermoregulatory center.
• Post-infection low-grade fever: Occurs when the thermoregulatory function has not fully recovered after a viral or other infection.
• Summer low-grade fever: Recurrent low-grade fever during summer, which resolves on its own in autumn.
• Physiological low-grade fever: Caused by factors like stress or intense exercise^[1].

TREATMENT

How to Relieve Low-Grade Fever?

• Maintain indoor temperature at around 20°C to 25°C;
• Get adequate rest, remove excess clothing, and choose appropriate bedding;
• Drink plenty of water (if health permits) to prevent excessive dehydration;
• Apply ice packs to areas with major blood vessels, such as the forehead (for infants), neck, armpits, or groin, for physical cooling;
• Use lukewarm water sponge baths for whole-body physical cooling;
• Consume light and easily digestible foods.

Note: If these measures fail to relieve the low-grade fever or if it progresses to a high fever, seek medical attention promptly for further diagnosis and targeted treatment.

How to Relieve Low-Grade Fever in Children?

Observe the child's mental state. If they appear alert and active, use physical methods to reduce fever, such as drinking warm water, applying cooling patches to the forehead, or wiping the body with lukewarm water.

Ensure the child stays in a comfortable and temperature-appropriate environment.

If the child shows poor mental state (e.g., lethargy, weakness, loss of appetite) or the fever persists for several days, seek immediate medical care.

DIAGNOSIS

When should you seek medical attention for a low-grade fever?

Seek immediate medical attention if a low-grade fever is accompanied by the following symptoms:

• Persistent low-grade fever lasting more than three days;
• Recurrent low-grade fever;
• Cough, phlegm, chest pain, night sweats, fatigue, weight loss, loss of appetite, swollen lymph nodes, etc.;
• Abdominal bloating, pain, diarrhea, jaundice, etc.;
• Sore throat, etc.;
• Joint swelling and pain, circular skin erythema, skin purpura (red bleeding spots on the skin), subcutaneous nodules, etc.;
• Frequent urination, urgency, pain during urination, etc.;
• Pale complexion, palpitations (such as unease, rapid heartbeat, etc.), bleeding, etc.

What tests are needed for a low-grade fever?

• Medical history inquiry: Before testing, the doctor will ask about symptoms such as cough, abdominal pain, or diarrhea to understand potential causes. Patients should answer truthfully.
• Physical examination: The doctor will also check for signs like swollen lymph nodes; measure body temperature to observe if the underarm temperature indicates fever without exceeding 38°C, aiding in a preliminary diagnosis.
• Complete blood count (CBC): A blood test to measure white blood cell and neutrophil counts, helping determine if an infection is present and assisting in diagnosis.
• Urinalysis: Used to identify the cause, observing urine for unusual odor, leukocyturia (white blood cells in urine), hematuria (blood in urine), proteinuria (protein in urine), etc., to assess for urinary tract infections.
• Brain CT: Used to determine the cause, examining head images for abnormalities and assessing for intracranial infections or lesions.
• Chest and abdominal X-ray: Examines the structure of chest and abdominal tissues and organs to identify space-occupying lesions and differentiate conditions like pneumonia, pleurisy, or pancreatitis.
• Tuberculin skin test: Involves intradermal injection of tuberculin to analyze results and determine the presence of tuberculosis.

POTENTIAL DISEASES

What are the possible causes of low-grade fever?

• Infectious low-grade fever: Bacterial infections, such as chronic bronchitis, bacterial pneumonia, chronic tonsillitis, chronic sinusitis, gingivitis, chronic cholecystitis, chronic appendicitis, urinary tract infections, chronic pelvic inflammatory disease, chronic prostatitis, tuberculosis, syphilis, etc.; viral infections, such as acute upper respiratory tract infections, chronic viral hepatitis, AIDS, etc.; fungal infections, such as candidal pneumonia, candidal vaginitis, etc.; parasitic infections, such as toxoplasmosis, etc., can all cause low-grade fever^[1].
• Non-infectious low-grade fever: Aseptic necrotic material absorption fever, such as postoperative low-grade fever, low-grade fever after internal bleeding, post-myocardial infarction low-grade fever, post-pulmonary embolism low-grade fever, malignant tumors, leukemia, lymphoma, etc.; antigen-antibody reaction fever, such as rheumatic fever, drug fever, connective tissue diseases, etc.; endocrine and metabolic disease fever, such as hyperthyroidism, dehydration; reduced skin heat dissipation, such as extensive dermatitis, ichthyosis, etc., can also cause low-grade fever^[1].
• Functional low-grade fever: Such as autonomic nervous system dysfunction, low-grade fever after infection recovery, summer low-grade fever, physiological low-grade fever, etc.^[1].