Fever with Chronic Diseases: Higher Risks and What to Monitor

Fever itself is not a disease, but a sign that your body is fighting an infection. In generally healthy adults, a raised temperature is often unpleasant but harmless. If you live with chronic conditions, however, you have a higher risk of complications and serious illness.

Why fever is riskier if you live with chronic disease

Important chronic conditions include:

• diabetes mellitus (type 1 and type 2)
• chronic heart failure and other heart disease
• chronic lung disease (for example COPD, asthma)
• chronic kidney disease
• cancer and chemotherapy
• autoimmune diseases treated with steroids, immunosuppressants or biologics
• after an organ transplant
• older age, frailty or known immunocompromise

These conditions reduce the reserve of your heart, lungs and kidneys or weaken your immune system. Your body may not be able to fight infection as well, symptoms can be atypical, and complications such as pneumonia, heart failure or sepsis can develop faster.

In older adults, a serious infection may show up first as confusion, falls or a sudden decline in daily function even if the temperature is only slightly raised or normal.

Quick triage: When fever is an emergency

In adults, a temperature of around 38.0 °C (100.4 °F) or higher is usually considered a fever. For otherwise healthy adults, the following is a rough guide:

If you have underlying conditions, you should act earlier. Do not focus only on the number on the thermometer – duration of fever and red-flag symptoms are just as important.

Red-flag symptoms – seek urgent or emergency care

Contact your doctor, urgent care service or emergency department immediately if you have fever and any of the following warning signs:

• difficulty breathing, fast or laboured breathing, blue lips or severe shortness of breath (especially with COPD or asthma)
• chest pain, new or much worse leg swelling, very fast heartbeat
• confusion, drowsiness, loss of consciousness, seizures
• stiff neck, severe headache, sensitivity to light
• ongoing vomiting or diarrhoea, or you cannot keep fluids down
• signs of dehydration (very little or dark urine, intense thirst, dizziness, very dry mouth)
• a new widespread rash, tiny red or purple spots (petechiae) or unexplained bruising
• very low blood pressure, cold, pale or mottled skin – possible sepsis (blood poisoning)
• fever after chemotherapy, in known severe immunocompromise or after organ transplantation

If you are unsure, it is safer to seek medical advice early – by phone, telemedicine or in person – rather than waiting.

What to monitor at home: the fever checklist

With chronic disease, it is not enough to just glance at your temperature. Monitoring several key areas helps you and your healthcare team spot problems early.

1. Temperature: measure correctly and track trends

Use a reliable thermometer and measure in the same place each time. Rectal temperature is often the most accurate.

• check your temperature at least 2–4 times per day
• write down temperature, time, any fever medicine you take and how you feel
• watch for trends: is the fever going up, staying the same or going down?

2. Fluids and urine output – avoiding dehydration

Fever increases your need for fluids. At the same time, some people with heart failure or chronic kidney disease have to limit how much they drink. Ask your healthcare team for a personal sick-day plan.

Pay attention to:

• how much you drink (for example water, unsweetened tea, clear broth – within your prescribed limits)
• how often and how much you urinate (very dark or little urine is a warning sign)
• dizziness when standing up, dry mouth and tongue, reduced skin turgor – possible dehydration

3. Breathing, heart and circulation

In chronic heart or lung disease, an infection can quickly trigger deterioration. Monitor:

• breathing rate (if it becomes clearly faster than usual, this is a warning sign)
• shortness of breath at rest or with light activity, wheezing in asthma/COPD
• heart rate and blood pressure if you have monitors at home

4. General condition and mental state

Take changes in how you feel seriously, even when the temperature is not extremely high. In older adults and people with frailty, the following signs may indicate a serious infection:

• unusual tiredness or extreme weakness
• new or worsening confusion, disorientation, agitation
• sudden loss of independence in everyday activities (walking, dressing, eating)

5. Extra checks for specific chronic conditions

Diabetes mellitus:

• check blood glucose more often (for example every 2–4 hours or as advised)
• check for ketones in urine or blood if your glucose is high or you feel unwell
• if you cannot eat normally, use easy-to-tolerate drinks or small snacks that contain carbohydrates
• do not stop insulin or other diabetes medicines on your own – only adjust doses with professional guidance

Heart failure:

• weigh yourself daily (ideally in the morning after getting up)
• a sudden weight gain of more than about 2 kg (4–5 lb) over a few days may mean fluid overload
• worsening breathlessness, especially when lying flat, or sudden night-time cough are warning signs

Chronic kidney disease:

• keep to the fluid allowance agreed with your kidney team
• monitor urine output (amount, colour, frequency)
• only take painkillers and other medicines that can affect the kidneys if your doctor has confirmed they are safe for you

COPD or asthma:

• track cough, sputum (colour, amount) and breathlessness
• follow your written action plan (for example increased inhaler doses, short steroid course if prescribed)
• seek medical help early if you are getting more breathless

Immunocompromised, chemotherapy or organ transplant:

• in many of these situations a fever from around 38.0 °C (100.4 °F) is treated as a medical emergency
• follow the emergency pathway given by your specialist team
• do not delay seeking help at night or on weekends – time matters

Medicines for fever: what people with chronic disease should know

Paracetamol / acetaminophen

Paracetamol is often the first-line option to relieve fever and pain. If you have liver disease or take other products that contain paracetamol, there is a risk of liver damage. Never exceed the maximum daily dose stated on the label.

Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or diclofenac

NSAIDs can reduce kidney function and may worsen heart failure by causing fluid retention and raising blood pressure. If you have chronic kidney disease, heart failure or are older, only use these medicines on professional advice.

Prevention and preparedness: before the next infection

• Check that your vaccinations are up to date (for example influenza, COVID-19 and pneumococcal vaccines if recommended for you)
• Work with your healthcare team to create a written sick-day plan
• Keep important phone numbers handy (primary care, specialists, out-of-hours and emergency services)
• Prepare a small sick-day kit at home: thermometer, supply of regular medicines, and if advised, devices for monitoring

"Fever with chronic disease is not a reason to panic – but it is a reason to monitor closely and seek help early if warning signs appear."

FAQs – Common questions about fever with chronic disease

What temperature counts as a fever in adults?

In adults, a temperature from around 38.0 °C (100.4 °F) is usually called a fever. However, your overall condition and symptoms matter more than the exact number.

How long can a fever last?

In otherwise healthy adults, a mild viral illness with fever often settles within 3–5 days. If you have chronic disease, seek medical advice if fever lasts more than 48–72 hours or gets worse.

Why does fever raise my blood sugar?

Infection and illness are stressful for the body. Stress hormones such as adrenaline and cortisol raise blood glucose to make more energy available to the immune system.

When is it safe to manage fever at home?

If your fever is mild, you can drink enough, you feel stable and you do not have red-flag symptoms, self-care at home is often appropriate: rest, fluids, light food and, if suitable for you, a fever-reducing medicine.

Important: This article provides general information and is not a substitute for medical advice. Always discuss your individual situation with your healthcare professionals.