Blood tests before chemotherapy: what counts you need for a cycle

Before every chemotherapy cycle, your doctor looks at a full blood count and blood chemistry. The point is to make sure your bone marrow has recovered from the last treatment and that your liver and kidneys can handle the drugs. For most regimens, a cycle goes ahead if the absolute neutrophil count is at least 1.5×10⁹/L and platelets are at least 100×10⁹/L. Some regimens have their own rules, though, so the final decision is always your oncologist's.

Why you need a blood test before every cycle

Many chemotherapy drugs act on rapidly dividing cells. A tumor is not the only tissue like that: your bone marrow is constantly making new blood cells, and chemotherapy temporarily suppresses it. This is called myelosuppression.

If the next cycle starts before your blood has recovered, the risk of serious infection and bleeding goes up. So the pre-cycle test is not a formality; it is a safety check.

According to the practical guidelines of RUSSCO (the Russian Society of Clinical Oncology):

• before the first cycle, a full blood count is done no more than 14 days before treatment starts;
• before each following cycle, a full blood count is done no more than 5 days in advance, and blood chemistry no more than 7 days.

What your doctor looks at

The neutrophil and platelet thresholds come from the RUSSCO guidelines, which also note that weekly paclitaxel, gemcitabine, BEP/EP regimens and some others use special criteria. So the table above is a reference point, not a rule for your specific regimen.

ANC (absolute neutrophil count) is not the same as the white blood cell count. Neutrophils are one type of white blood cell, and it is their number your doctor is looking at. If your report only shows a neutrophil percentage, ANC is calculated by multiplying the total white cell count by the neutrophil percentage (band and segmented neutrophils together).

Liver and kidney tests. There is no single threshold for bilirubin, ALT or creatinine — it all depends on which drugs are in your regimen and how they leave the body. For example, RUSSCO lists creatinine clearance below 50–60 mL/min as a relative contraindication to cisplatin. With other drugs, liver or kidney function may affect the dose.

What the nadir is, and why a mid-cycle test can look “scary”

The nadir is the lowest point your blood counts reach after treatment. According to the Canadian Cancer Society, white cells and platelets usually reach their nadir about 7–14 days after treatment and generally start to recover within 2–4 weeks. Red blood cells live longer, so their nadir comes later.

That explains a common situation: someone has a blood test on day 10, sees a low white count and panics. It may simply be the expected nadir. In fact, RUSSCO does not recommend routine blood checks earlier than 7 days after the start of a cycle if you have no symptoms.

Low counts mid-cycle are often expected on their own. The danger is not the numbers themselves but fever, bleeding or feeling worse while your counts are low.

How to tell from how you feel that your counts have dropped

A blood test is the main tool, but your body sends signals too. The Canadian Cancer Society describes the signs for each type of blood cell.

Low white cells and neutrophils don't cause any symptoms by themselves — you can't feel them. What shows up is the infection: fever, chills.

Low platelets: bruising from a light touch, bleeding gums or nosebleeds, tiny red spots on the skin (petechiae), blood in the urine, dark or black stools.

Low hemoglobin (anemia): tiredness, pale skin, lips and nails, a fast heartbeat, shortness of breath and getting tired quickly with activity, dizziness, headache.

If any of these signs appear between cycles, tell your doctor, even if your next blood test is still a few days away.

How to do your tests without losing time

A few practical habits that save both nerves and days:

• ask your doctor which day to have blood taken and how to send the result — then the decision about your cycle is made in advance, not on the day of treatment;
• if you can, use the same lab each time so results are easier to compare;
• keep a table: date, neutrophils, platelets, hemoglobin, bilirubin, creatinine and cycle date — that way you can see the trend from cycle to cycle;
• don't take anything on your own “to raise white cells” or “for the liver” — some of these products can interact with your treatment.

Why a cycle may be postponed

A cycle may be postponed if:

• neutrophils or platelets are below the threshold for your regimen;
• side effects from the last cycle (other than hair loss) have not yet settled to grade 0–1, meaning mild or gone;
• a chronic condition has flared up or an acute illness, such as an infection, has developed.

RUSSCO allows a cycle to be moved by 3 days either way even without a medical reason — for example, because of public holidays. That is normal flexibility, not a break in treatment.

If delays keep happening or side effects were severe, your doctor may lower the dose. Under the RUSSCO guidelines, for clinically significant grade 3–4 side effects (other than blood-related ones), the dose is usually reduced by 20–40%. I explain how a treatment cycle works overall in my article on what chemotherapy is like.

G-CSF: injections that support neutrophils

G-CSF (granulocyte colony-stimulating factor) drugs stimulate the bone marrow to make neutrophils faster. They are used to lower the risk of febrile neutropenia (fever with low neutrophils) and to avoid delaying cycles.

According to the RUSSCO guidelines on febrile neutropenia:

• G-CSF prevention is given if the risk of febrile neutropenia with a given regimen is above 20%;
• with a risk of 10–20%, the doctor assesses additional risk factors for the individual patient;
• prevention is also considered when the bone marrow is depleted, including in patients over 65;
• G-CSF is started no earlier than 24 hours after chemotherapy and stopped no later than 48 hours before the next cycle.

Don't start G-CSF on your own: the drug, timing and duration are chosen by your oncologist for your specific regimen.

When your results or symptoms mean you should call your doctor right away

Call your oncologist or your clinic's on-call service immediately, without waiting until morning, if:

• your temperature is 38.0 °C or higher for more than an hour, or rises once to 38.3 °C or higher — these are the RUSSCO criteria for febrile neutropenia when measured by mouth (for underarm readings, the thresholds are 0.2 °C lower);
• you have chills or sweating, or cold, clammy, pale skin;
• you develop a cough, shortness of breath, pain when urinating, or confusion;
• your gums or nose bleed, tiny red spots appear on your skin, you bruise for no reason, there is blood in your urine, or your stools are black.

Don't bring the fever down with fever-reducing medicine before you call, unless your doctor has told you otherwise — the American Cancer Society advises checking with your treatment team first.

Call your local emergency number (911 in the US, 999 in the UK, 112 in the EU) if breathing is difficult, the person is confused or hard to wake, or there is heavy bleeding that won't stop.

For more on what to do about a fever during treatment, see my article on febrile neutropenia. If your blood results between cycles raise questions and it's hard to reach your oncologist, I can go through them with you in an online consultation.

Questions to ask your oncologist

• What blood count thresholds apply to my regimen?
• Which day before the cycle should I have blood taken, and where should I send the result?
• Do I need a mid-cycle blood test?
• Should I have G-CSF prevention?
• At what temperature and with which symptoms should I call you, and when should I call an ambulance straight away?

Sources

1. General principles of anticancer drug therapy. RUSSCO practical guidelines, part 1 — RUSSCO, 2023
2. Practical guidelines for the diagnosis and treatment of febrile neutropenia — RUSSCO, 2023
3. Low blood cell counts — Canadian Cancer Society
4. Fever — American Cancer Society, 2024