Fever in Older Adults: Why It Can Be Subtle and When to Call

What fever is and why it matters

A fever is a rise in body temperature, usually due to the immune system responding to infection or inflammation. In adults it is commonly defined as a temperature of 38.0 degrees Celsius (100.4 degrees Fahrenheit) or higher. Fever is a sign, not a disease. It can come from infection but also from other causes, such as certain medicines, inflammation, blood clots, heat illness and some cancers.

In older adults, temperature regulation is less efficient. Many have a lower resting temperature, for example about 36 degrees Celsius, so a reading of 37.5 degrees Celsius might be a meaningful rise for them even though it would look normal on a general chart. Geriatric guidance, such as that from infectious disease societies for older residents in long-term care, counts a smaller sustained rise over the person's baseline as significant. This is why knowing your parent's usual temperature, measured when well, is useful. See digital thermometers: choosing and using them for older people.

Why fever may be absent or small

• Blunted immune response with age.
• Lower baseline temperature.
• Medicines such as steroids, some anti-inflammatory drugs and others may suppress fever.
• Poor nutrition and frailty.
• Serious infection can overwhelm the body so that temperature falls instead of rising.
• Dementia may mean the person cannot say they feel unwell.

So a normal thermometer reading does not exclude infection. Treat the whole picture.

Other signs that may point to infection

In older adults, watch for:

• New confusion, agitation, drowsiness or a change in behaviour or alertness. This can be delirium, a medical emergency; see delirium in older adults.
• A fall or new unsteadiness.
• Loss of appetite, reduced drinking or refusing food.
• Weakness, unusual tiredness, or staying in bed.
• Fast breathing, cough, breathlessness or new wheeze.
• Fast pulse or low blood pressure with dizziness.
• Burning or frequent urination, foul-smelling urine or new incontinence.
• Redness, warmth, swelling or pus around a wound, pressure sore, foot ulcer or catheter site.
• Shivering or sweats, rigors.
• Diarrhoea, vomiting or abdominal pain.
• Pain in the ear, throat or teeth.
• Skin that is cold, clammy, mottled or very pale.

Any one of these, with or without fever, deserves attention.

How to check at home

When your parent seems unwell:

1. Temperature: Take it properly, by the same method each time; record the method. Retake after 15 to 30 minutes if the reading is odd. 2. Pulse and blood pressure: A very fast pulse, or low blood pressure, are warning signs. See how to measure blood pressure at home accurately. 3. Oxygen saturation: If you have an oximeter, check, bearing in mind its limits; see pulse oximeters: how they work and pulse oximeter accuracy. 4. Breathing rate: Count breaths over one minute while the person is at rest. More than about 20 a minute at rest is a concern in many settings; more than 24 is a stronger warning. 5. Alertness: Are they their usual self? Can they answer questions, recognise you, and stay awake? 6. Drinking and urine: How much fluid are they taking? Is the urine very dark, scanty or foul-smelling? 7. Blood sugar, if your parent has diabetes and a meter; see how to test blood sugar at home step by step. 8. Look at skin, feet, wounds, and pressure areas.

Record the numbers with the time, and note symptoms. Writing them on one page speeds the phone call to the doctor. See monitoring an older adult during an acute illness at home.

What to do at home while you seek advice

• Call the doctor early rather than waiting several days. Older adults can deteriorate quickly.
• Offer fluids in small, frequent sips, unless the doctor has restricted fluids for heart or kidney disease. Dehydration worsens confusion and kidney strain.
• Dress lightly and keep the room comfortable, rather than piling on blankets or opening every window.
• Ask about medicines. Do not start or stop prescription medicines on your own. If you plan to give a fever or pain medicine, ask the doctor or pharmacist which one and how much is safe for your parent, considering their other medicines, kidney function, stomach and liver. Avoid doubling up on products that contain the same ingredient, such as combined cold remedies.
• Do not use cold baths or alcohol rubs to bring down temperature.
• Check frequently but not obsessively; every few hours is usually enough unless the doctor says otherwise.
• Stay with your parent or arrange regular checks, especially at night.

When to call the doctor the same day

• A temperature of 38.0 degrees Celsius or above, or a rise of a degree or more above your parent's usual reading.
• A normal temperature but new confusion, fall, poor drinking, weakness or fast breathing.
• Symptoms of urinary infection, chest infection, skin infection or diarrhoea.
• Fever lasting more than 24 to 48 hours or coming back.
• Fever in someone with diabetes, kidney disease, heart failure, cancer treatment, or on steroids or other medicines that lower immunity.
• Fever after a hospital stay, surgery, a catheter, or a new wound.

When to call 112 or go to hospital

• Very drowsy, hard to wake, or very confused.
• Difficulty breathing, breathing very fast, blue or grey lips.
• Cold, clammy, mottled or very pale skin, or a very fast weak pulse, or fainting.
• Stiff neck, severe headache, or a rash that does not fade when pressed.
• A fit.
• No urine passed for many hours with illness.
• Temperature above about 40 degrees Celsius or below about 35 degrees Celsius.
• Chest pain, severe abdominal pain or a swollen, hot, painful leg.
• Any time you feel something is seriously wrong.

Sepsis, a life-threatening reaction to infection, can look like any of these, and speed matters. Guidelines such as NICE's NG51 emphasise early recognition. If in doubt, seek help.

Heat-related illness

In Indian summers, heat stroke is a real risk for older adults, especially in poorly ventilated homes or during power cuts. It can cause a high temperature, hot dry or sweaty skin, headache, confusion and collapse. It is an emergency: cool the person gently, move to shade and call 112. See also a pollution season plan for older adults for other seasonal risks.

Prevention

• Vaccines as advised by the doctor, such as influenza and pneumococcal; see vaccines that protect older lungs.
• Hand hygiene, careful food and water safety.
• Good mouth, skin and foot care, and prompt treatment of wounds.
• Adequate fluids and nutrition.
• Managing long-term conditions well.
• Avoiding unnecessary contact with sick visitors during outbreaks.

Making a baseline

When your parent is well, take their temperature at the same time of day on a few occasions and write down the usual reading and method. Keep the number in the family's health record; see keeping a health record at home. This helps recognise a change.

When to ask a professional

Ask your doctor what temperature or symptom should prompt a call for your parent, in light of their conditions and medicines. Ask about vaccines and a plan for infections. Seek help early for any fever or any unexplained change in behaviour, appetite or alertness. Call 112 for severe symptoms listed above.