Diagnosis and tests

Which signs need urgent assessment

With leukemia, some signs cannot wait. This topic explains when to seek help straight away, why time matters and how to be prepared in advance.

Last updated: 14 October 2026~3 min read

A phone glowing on a bedside table at night beside a thermometer, a warm lamp just switched on. — **Figure 1.**Even at night, call about an urgent sign.

01Short answer

Leukemia can cause emergencies both before diagnosis and during treatment. The most important is fever: when neutrophils are low, an ordinary infection can turn into sepsis within hours, so a temperature of 38 °C or higher needs an immediate call. Other warning signs are heavy bleeding or bleeding that will not stop, blood in vomit or stool, sudden severe headache, changes in vision, confusion, struggling to breathe, chest pain, passing much less urine, and swelling of one leg or arm. In acute promyelocytic leukemia (APL) the risk of bleeding is especially high. With these signs, do not wait until morning: call your team or, if you cannot reach them, emergency services.

02Simple explanation

Fever. When defence cells are low, the body cannot hold back an infection. So fever here is not a sign of a cold but an urgent signal.

Bleeding. When platelets are very low, a nosebleed may not stop, and blood can appear in vomit or stool. A severe headache can be a sign of bleeding in the brain.

Breathing and alertness. Breathlessness, chest pain, confusion and drowsiness can point to low oxygen or a serious infection.

Other signs. Passing less urine, a swollen leg, swelling of the face and neck, and severe abdominal pain should not wait either.

03Scientific explanation

Neutropenic fever: according to the NCI and CRUK, when neutrophils are very low an infection spreads fast, and neutropenic sepsis is life-threatening. Hospitals therefore aim to start intravenous antibiotics within the first hour.

APL and bleeding: according to the LLS, acute promyelocytic leukemia can disturb blood clotting (DIC), with a high risk of serious bleeding. That is why treatment starts immediately when APL is suspected.

Leukostasis: with a very high white count the blood can become “sludgy”, causing breathlessness, visual problems and confusion, and needs urgent treatment.

04What happens in the body?

Why does time matter so much?

Some conditions, such as neutropenic sepsis, bleeding in the brain and leukostasis, can worsen within hours. Arriving early gives doctors the chance of simpler and safer treatment.

Soft ambulance lights reflecting on wet asphalt on a quiet evening street. — **Figure 2.**Urgent help works best when it comes early.

How to be prepared

Keep your team’s 24-hour number on your phone and on paper. Have a thermometer at home. Keep your medicines list, latest results and discharge summary in one folder. Pack a small bag in advance.

A small bag by the door with a folder of medical papers, a medicines list and a charger. — **Figure 3.**A bag packed in advance saves time.

What to say when you call

Give your diagnosis, the date of your last chemotherapy, your temperature and when you took it, and any other signs. Saying “I may be neutropenic” helps.

05What to do with a warning sign

Four simple steps.

1MeasureTemperature and how you feel.

2CallYour team or emergency services.

3Take your papersMedicines, discharge summary, results.

4AssessmentTests and treatment in hospital.

Fever38 °C or higher: now.

BleedingWill not stop: now.

AlertnessConfusion: now.

06Urgent signs

Sign	Possible cause	What to do?
Temperature 38 °C or higher	Infection with neutropenia	Call your team straight away
Bleeding that will not stop, blood in vomit	Low platelets, DIC	Emergency services
Sudden severe headache, vision change	Bleeding in the brain, leukostasis	Emergency services
Breathlessness, chest pain	Infection, clot, anemia	Emergency services
Confusion, severe drowsiness	Sepsis, metabolic upset	Emergency services
Swelling and pain in one leg	Deep vein thrombosis	Seek care the same day

* When in doubt, always call.

07Key terms

Neutropenic fever: Fever when neutrophils are low.
Sepsis: A dangerous whole-body reaction to infection.
DIC: A clotting disorder causing both clots and bleeding at once.
Leukostasis: Disturbed blood flow due to a very high white count.
APL: Acute promyelocytic leukemia, a special type of AML.

08Key points

Temperature 38 °C or higher: call straight away.
Bleeding that will not stop is an emergency.
Confusion and breathlessness cannot wait.
Call even at night.
Keep numbers and papers ready.
An early call makes treatment simpler.

09Frequently asked questions

Can I take a fever reducer and wait?

No. The medicine can hide the fever while the infection carries on. Call your team first.

It is night; can I wait until morning?

Not with urgent signs. Hematology wards are ready for night calls.

Which hospital should I go to?

Ideally the centre where you are treated. If it is far, go to the nearest emergency department and tell them about your leukemia.

Is a small nosebleed urgent too?

If it stops after 10–15 minutes of pressure, let your team know. If it will not stop, you need urgent help.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

Can I take a fever reducer and wait?
It is night; can I wait until morning?
Which hospital should I go to?
Is a small nosebleed urgent too?

My questions

12Sources

NHS. Acute myeloid leukaemia: Symptoms
American Cancer Society. Signs and Symptoms of Acute Myeloid Leukemia
National Cancer Institute (NCI). Infection and Neutropenia during Cancer Treatment
NHS. Sepsis
Cancer Research UK. Acute promyelocytic leukaemia (APL)
MedlinePlus. Recognizing medical emergencies
Blood Cancer United (formerly The Leukemia & Lymphoma Society). Hairy cell leukemia (HCL) diagnosis
Cancer Research UK. Symptoms of hairy cell leukaemia
Cancer Research UK. Getting diagnosed with hairy cell leukaemia
Hairy Cell Leukemia Foundation. Hairy Cell Leukemia Foundation — information for patients

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 14 October 2026← Back to the list

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