Let’s Talk About Blood Counts During Chemotherapy
Disclaimer: This content is written by a practicing oncologist for informational purposes only. It does not replace your doctor’s advice. This does not constitute medical advice. Never change your treatment without consulting your care team.
Why Do We Talk So Much About Blood Counts?
When you start chemotherapy, you will hear a lot about “blood counts.” There are two reasons this topic comes up so often:
First, almost all chemotherapy drugs affect blood counts to some degree—it is the most common side effect of chemotherapy. Second, low blood counts can be serious: low white cells can lead to life-threatening infections, and low platelet counts increase the risk of bleeding.
Fortunately, low blood counts following chemotherapy are a predictable and well-understood side effect. We know when to expect them to drop, how to monitor them, how to prevent them from falling dangerously low, and how to manage them when they occur. You need to be watchful for warning signs and contact your treatment team early if something seems wrong.
This article will help you understand why chemotherapy affects blood counts, what symptoms to watch for, and what you can do to stay safe during treatment.
Why Does Chemotherapy Cause Low Blood Counts?
The bone marrow is specialised tissue inside your bones—your body’s “blood factory.” It constantly produces three types of cells:
- White Blood Cells (WBCs): WBCs are of many types. They fight infection. Chemotherapy primarily affects neutrophils, the most numerous white blood cell and the main defence against infection. When neutrophils are low, it is called neutropenia.
- Red Blood Cells (RBCs): RBCs carry oxygen and give you energy. Low red blood cells cause anaemia.
- Platelets: Platelets help your blood clot. When these are low, it is called thrombocytopenia.
Chemotherapy targets cells that divide rapidly. Cancer cells divide rapidly, but so do bone marrow cells. This is why chemotherapy suppresses the bone marrow and causes low blood counts. This is a trade-off on the path to cancer cure—an expected consequence of treatment, not a sign that something is wrong with your body.
This is also why chemotherapy is given in cycles, with a gap of weeks between doses. The gap allows the bone marrow to recover. The blood tests done during this period confirm that counts have recovered before the next cycle begins.
The Timeline of Blood Count Suppression and Recovery
Blood counts do not drop immediately after chemotherapy. They fall gradually, reaching their lowest point (the nadir) around 7 to 14 days after your dose, then recover by the end of the third week. The second week after chemotherapy is therefore the period of highest risk—this is when you need to be most careful and watchful for symptoms.
Understanding this timeline helps you anticipate when your blood counts will be at their lowest. During the first few days after chemotherapy, counts remain relatively normal. You may experience nausea, fatigue, or other immediate side effects, but infection risk is not yet elevated. As you enter the second week, counts begin to fall. By days 10–14, most patients reach their nadir. This is when the risk of infection and bleeding is highest. After the nadir, counts begin to recover, and by day 21, most patients have recovered sufficiently to receive the next cycle.
Some chemotherapy drugs cause a longer or deeper nadir. Others have minimal effect on blood counts. You can ask your treating team what effects the chemotherapy you are receiving will have and when counts are expected to be at their lowest.
Why We Check Blood Counts Frequently
During chemotherapy, you will have your blood counts checked regularly—sometimes before each cycle, sometimes more frequently. These blood tests serve several purposes:
- Before each cycle: We check counts to ensure they have recovered sufficiently. If they are too low, we may delay chemotherapy to allow further recovery.
- During the nadir period: In some chemotherapy regimens, counts are checked during the expected nadir to assess the depth of suppression and determine if intervention is needed.
- When you have symptoms: If you develop fever or other symptoms suggesting infection or bleeding, a blood test helps us assess severity and guide treatment.
Do not be alarmed by frequent blood tests. Monitoring blood counts is a routine and essential part of chemotherapy care. It allows us to detect problems early and intervene before complications become serious.
Warning Signs of Low Blood Counts
Low blood counts can lead to serious complications. Low neutrophils make you vulnerable to infections that can spread rapidly. Low platelets increase your risk of bleeding, including bleeding into the brain. These complications can be prevented with timely treatment—antibiotics and hospital admission for infection, platelet transfusion for bleeding risk.
If you experience any of the symptoms listed below, contact your treating team immediately. Do not wait to see if symptoms improve on their own.
Signs of Low White Cells (Neutropenia)
Neutropenia itself causes no symptoms. You may feel completely normal even when your white cells are dangerously low. The danger of neutropenia is that it leaves you vulnerable to infection—and infections that would normally be minor can become serious rapidly when neutrophils are not available to fight them. This is why we watch for signs of infection: infection is what makes neutropenia dangerous, and the symptoms of infection are the warning that low counts have become a problem.
- Fever ≥100.4°F (38°C)
- Chills or shivering (with or without fever)
- Cough, especially with shortness of breath or chest pain
- Sore throat, mouth sores, white patches in the mouth, or difficulty swallowing
- Diarrhoea (more than 3 loose stools per day)—can indicate gut infection
- Discomfort around the anus or when passing stools
- Feeling very unwell, even without other symptoms
Fever with neutropenia is a medical emergency. Infections can progress within hours when neutrophils are low. Do not wait until morning or until the clinic opens—seek care immediately.
Signs of Low Red Cells (Anaemia)
Unlike low neutrophils and low platelets, low red blood cells develop gradually. Symptoms include:
- Unusual tiredness that does not improve with rest
- Shortness of breath during routine activities (walking, climbing stairs)
- Dizziness or lightheadedness, especially when standing
- Rapid heartbeat—feeling like your heart is racing or fluttering
These symptoms are not emergencies in the same way fever is, but they should be reported to your treating team so your counts can be checked and treatment arranged if needed.
Signs of Low Platelets (Thrombocytopenia)
Any bleeding on chemotherapy may indicate low platelet counts:
- Bleeding gums—heavy bleeding when brushing teeth or eating
- Tiny red or purple spots on the skin (petechiae)—look like pinpricks, do not fade when pressed
- Bruises appearing without known injury
- Blood in urine (pink or red) or stool (black or tarry)
- Nosebleeds that are difficult to stop
- Unusually heavy menstrual bleeding
If you notice any of these signs, contact your treating team so platelet levels can be checked.
Prevention of Low Blood Counts
One of the most significant advances in chemotherapy supportive care has been the development of drugs that can prevent low blood counts. These are now routinely used in patients receiving chemotherapy regimens known to cause significant drops in counts.
- Filgrastim and Pegfilgrastim: Neutrophil production in the bone marrow is stimulated by a growth factor called G-CSF. Filgrastim is a synthetic version of G-CSF. It has a short duration of action and is administered as a daily injection. Pegfilgrastim is a long-acting version, given once per cycle, usually 24–48 hours after chemotherapy. These drugs reduce the depth and duration of neutropenia and lower the risk of febrile neutropenia.
- Erythropoietin and Darbepoetin: Erythropoietin is a hormone that stimulates red blood cell formation. Darbepoetin is a synthetic form with a longer duration of action, requiring less frequent administration. These drugs can reduce the need for blood transfusions in patients with chemotherapy-induced anaemia.
- Platelet growth factors: Romiplostim and eltrombopag stimulate platelet formation and may be used for low platelet counts after chemotherapy, though their use is less routine than G-CSF.
Your treating team will decide whether you need any of these drugs based on the chemotherapy regimen you are receiving and your individual risk factors. Not all patients require growth factor support—it depends on how significantly your particular chemotherapy affects counts.
Treatment of Low Blood Counts
The drugs described above take about a week to act. When blood counts are already low, treatment focuses on managing the consequences rather than waiting for counts to recover on their own:
- Low Neutrophils: Neutropenia itself does not always require treatment—counts usually recover within a few days. However, if you develop signs of infection (particularly fever), you will need hospitalisation and intravenous antibiotics. This is called febrile neutropenia, and it is treated as an emergency. Growth factors may be administered to hasten recovery.
- Low Platelets: Platelet transfusion is given when platelet counts fall below a safe threshold or when there is active bleeding. A single transfusion can raise levels enough to prevent or stop bleeding.
- Anaemia: Anaemia develops more slowly than neutropenia or thrombocytopenia because red blood cells have a longer lifespan. If rapid correction is needed—for example, if you are severely symptomatic—you may be given a blood transfusion. Haemoglobin levels improve immediately after transfusion.
Treatment Delays Due to Low Blood Counts
If your blood counts are too low on the day of your scheduled chemotherapy, treatment may be delayed by a few days to allow recovery. For many patients, this causes anxiety—they fear the cancer will grow back during the delay.
A short delay is a safety measure, not a setback. Administering chemotherapy when counts are already low increases the risk of prolonged and severe neutropenia or thrombocytopenia. The consequences of giving chemotherapy with inadequate counts—serious infection, bleeding requiring transfusion, prolonged hospitalisation—are worse than a brief delay.
A delay of a few days does not reduce the efficacy of treatment. Most chemotherapy regimens have built-in flexibility for this reason. Your treating team monitors your counts precisely so that treatment can proceed when it is safe to do so. Trust that a delay, when recommended, is in your best interest.
Practical Advice for Daily Life
Food Safety
You may have heard of “neutropenic diets” that restrict all raw foods. These diets are difficult to follow, and multiple studies have found no difference in infection rates between patients on strict low-microbial diets and those following standard food safety practices. Strict dietary restrictions are not necessary for most chemotherapy patients.
What matters is understanding two principles:
1. Guard against water contamination
When unboiled water is incorporated into food—blended, mixed, or frozen—any bacteria in that water will be present in the food. This applies to:
- Chutneys and sauces (water blended in)
- Fresh juices prepared with water
- Ice in drinks
- Diluted beverages
Raw fruits and vegetables are safe to eat if washed under running water before consumption.
2. Avoid stale food
Bacteria multiply rapidly in food stored at room temperature. Freshly cooked food served hot is safe. Food that has been sitting unrefrigerated for hours is not.
It is best to consume food cooked at home. When this is not possible, ensure what you eat is freshly prepared.
Personal Hygiene
- Maintain routine personal hygiene
- Keep your living space clean
- You do not need to isolate yourself in a separate room unless specifically instructed, but avoid unnecessary contact with people, particularly during the nadir period when counts are lowest
- Ask household members or visitors with cold or flu symptoms to avoid close contact
- If you have a central venous catheter, follow the care instructions provided
Preventing Bleeding (When Platelets Are Low)
- Use a soft-bristled toothbrush
- Use an electric razor rather than blades
- Avoid activities with high risk of falls or injury
- If you have been prescribed aspirin, ibuprofen, or other NSAIDs, inform your treating doctor—these medications can increase bleeding risk when platelets are low
Managing Fatigue (When Red Cells Are Low)
- Prioritise essential tasks
- Plan demanding activities for times when you have most energy
- Pace yourself—break tasks into steps with rest in between
- Stay hydrated
- Light physical activity, if tolerated, can help maintain energy levels
What to Tell Your Treating Team
When you contact your treating team with symptoms, be prepared to provide:
- Your temperature (take it before calling)
- The date of your last chemotherapy
- Your symptoms and when they started
- Any new medications you are taking
- Your most recent counts, if known
This information helps us assess the situation quickly and advise you appropriately.
Quick Reference: Glossary
| Term | Meaning |
|---|---|
| Myelosuppression | Bone marrow suppression; reduced production of blood cells |
| Nadir | Lowest point of blood counts, usually 7–14 days post-chemotherapy |
| Neutropenia | Low neutrophil count; increased infection risk |
| Febrile neutropenia | Fever during neutropenia—a medical emergency |
| Anaemia | Low red blood cells; causes fatigue and breathlessness |
| Thrombocytopenia | Low platelets; increased bleeding/bruising risk |
| Petechiae | Tiny red/purple skin spots from minor bleeding under the surface |
| G-CSF | Growth factor injection that boosts white cell production |
| CBC | Complete Blood Count—the blood test that measures all cell types |
Summary
- Low blood counts are the most common side effect of chemotherapy. Understanding blood counts helps you stay safe during treatment.
- Blood counts fall predictably after chemotherapy, reaching their lowest around days 7–14. This is when risk is highest.
- Fever ≥100.4°F (38°C) during this period is an emergency. Contact your care team immediately.
- Report symptoms early. Do not wait to see if they improve—infections can progress rapidly when counts are low.
- Know what to tell the clinic: your temperature, date of last chemotherapy, your symptoms, and any new medications.
- Preventive treatments (growth factor injections, sometimes prophylactic antibiotics) can reduce the risk of dangerous drops in counts.
- If your blood counts are low, a short treatment delay keeps you safe without compromising your outcome.
- Follow two food safety principles: avoid foods with unboiled water blended in, and avoid food that has been sitting at room temperature for hours.
Low blood counts are an expected part of chemotherapy. They are temporary, predictable, and manageable. Your treating team monitors your counts, provides preventive treatment when appropriate, and is available to help if complications arise. Your role is to understand when you are most vulnerable, recognise warning signs, and seek help early. Most patients get through chemotherapy without serious complications from low blood counts. With awareness and timely action, you can too.