Understanding Your Blood Test Results

Hemoglobin (Hb, HGB)

Hemoglobin is the iron-rich protein inside red blood cells that carries oxygen from your lungs to every tissue in your body, and it is one of the first numbers doctors check on a blood count. The full biology is in our dictionary entry on hemoglobin.

Low hemoglobin: what it can mean

A hemoglobin below your lab's range is called anemia. During cancer treatment it is most often a side effect of chemotherapy or radiotherapy suppressing the bone marrow — blood loss, iron or vitamin deficiency and the cancer itself are other causes. Doctors look at how far the value has fallen, how fast, and whether you have symptoms such as fatigue, breathlessness or a racing heart before choosing between watchful waiting, iron or other supplements, medicines that stimulate red-cell production, or a transfusion.

National Cancer Institute — Anemia and Cancer Treatment

High hemoglobin: what it can mean

A value above the range is less common and often reflects dehydration, smoking, lung or heart conditions, or living at high altitude; rarely it points to a bone-marrow condition that overproduces red cells. Doctors usually recheck it and read it together with the hematocrit and red-cell counts.

Lived experience from our network

Members of our CAYAS network describe low-hemoglobin weeks as the ones where stairs suddenly count double and afternoon naps stop being optional. Several only realised how anemic they had been once it was treated — colour and energy came back within days. Planning demanding things for the time of day when your energy peaks helps.

Worth asking your care team: Is my hemoglobin trending down, and at what value would we treat it rather than watch it?

Hematocrit (Hct, HCT)

Hematocrit is the share of your blood volume taken up by red blood cells, shown as a percentage or a fraction. It moves largely in step with hemoglobin and doctors read the two together — our dictionary entry on hematocrit explains the details.

Low hematocrit: what it can mean

A hematocrit below your lab's range usually points the same way as low hemoglobin: fewer red blood cells, i.e. anemia — from marrow-suppressing treatment, blood loss or the disease itself. Because the value also depends on how diluted your blood is, doctors first consider fluids: an infusion can lower the hematocrit without any change in your red cells.

MedlinePlus (NIH) — Hematocrit Test

High hematocrit: what it can mean

A value above the range most often reflects dehydration — the plasma volume shrinks, so the red-cell share rises — and also smoking or low oxygen levels; rarely, a bone-marrow condition that overproduces red cells. It is typically rechecked after you have had fluids.

Worth asking your care team: Do my hematocrit and hemoglobin tell the same story, or is one of them skewed by fluids or dehydration?

White blood cells (WBC, leukocytes)

The white blood cell count is the total of all your immune cells: neutrophils, lymphocytes, monocytes, eosinophils and basophils together. On many reports it is the number that decides whether the next chemotherapy cycle can go ahead. Our dictionary explains the whole white blood cell family.

Low white blood cells: what it can mean

A count below your lab's range (leukopenia) during treatment usually means the bone marrow is suppressed by chemotherapy or radiotherapy. What matters most to doctors is which cell type is low — above all the neutrophils — so a low total is always read together with the differential, the per-type breakdown on the same report.

MedlinePlus (NIH) — White Blood Count (WBC)

High white blood cells: what it can mean

A count above the range most often reflects infection or inflammation, corticosteroid medication, or growth-factor injections (G-CSF) given to speed recovery after chemotherapy. A persistent unexplained rise is followed up with the differential and a repeat test.

Lived experience from our network

In our network, "counts day" is a fixture of every cycle: the blood draw that decides whether chemotherapy goes ahead this week or waits. Survivors describe keeping plans loose for the days after it until the green light comes.

Worth asking your care team: Which of my white cell types is driving this number, and does it change my treatment schedule?

Neutrophils (ANC, absolute neutrophil count)

Neutrophils are the white blood cells that respond first to bacterial infection — and the ones chemotherapy hits hardest. Your report may show them as a percentage and as an absolute count (ANC); the absolute count is the one that matters clinically. More in our dictionary entry on neutrophils.

Low neutrophils (neutropenia): what it can mean

A count below the range is called neutropenia, the main reason infection risk rises during chemotherapy. The thresholds doctors act on usually come from your treatment protocol rather than the lab range alone: they weigh how deep the dip is, how long it lasts, and whether growth-factor support (G-CSF) or a treatment delay is needed. While your count is low, fever is urgent — call the number your team gave you instead of waiting it out.

National Cancer Institute — Infection and Neutropenia during Cancer Treatment

High neutrophils: what it can mean

A count above the range most often reflects infection, inflammation, corticosteroids, physical stress or a recent G-CSF injection. During treatment it is rarely a concern on its own and is usually simply rechecked.

Lived experience from our network

CAYAS members call them the "mask days": the stretch of each cycle when counts bottom out, visits are postponed, crowds are avoided and a thermometer lives on the nightstand. Knowing roughly when your nadir — the lowest point — is expected makes those days much easier to plan around.

Worth asking your care team: At what neutrophil count would you delay treatment or add growth-factor support — and what exactly is my plan if I get a fever?

Eosinophils

Eosinophils are the white blood cells most involved in allergic reactions and in defence against parasites. They are a small fraction of the total white count, which is why the absolute number — not the percentage — is the one to check. Our dictionary entry on eosinophils covers their biology.

Low eosinophils: what it can mean

A low eosinophil count is usually not a finding doctors act on: values near zero can be entirely normal, and corticosteroids — common alongside chemotherapy — push eosinophils down. If your report flags it, it generally matters far less than the neutrophil and total white-cell numbers next to it.

MedlinePlus (NIH) — Eosinophil Count

High eosinophils: what it can mean

A count above the range (eosinophilia) most often reflects allergies, skin conditions, drug reactions or parasitic infection; some medicines used in cancer care can raise it too. Doctors look at how high it is, whether it persists, and what changed recently — new medicines included — before investigating further.

Worth asking your care team: Is my eosinophil count something to follow up, or an expected effect of my current medication?

Platelets (PLT, thrombocytes)

Platelets are the small cell fragments that plug damaged blood vessels and start clotting. Chemotherapy commonly lowers them, typically a week or two into each cycle. See our dictionary entries on platelets and on the platelet count itself.

Low platelets (thrombocytopenia): what it can mean

A count below the range raises bleeding risk: easy bruising, nosebleeds, bleeding gums, or pinpoint red dots on the skin (petechiae). Doctors weigh how low the count is, whether you are actually bleeding, and what comes next in your treatment. A mild dip is often just watched; deeper ones can delay chemotherapy, and at the low values defined in your protocol a platelet transfusion may be given.

National Cancer Institute — Bleeding and Bruising (Thrombocytopenia)

High platelets: what it can mean

A count above the range (thrombocytosis) is often reactive — inflammation, infection, iron deficiency, or the rebound after chemotherapy — and frequently temporary. A persistently high count is followed up, and your doctor will also consider clotting risk in your particular situation.

Lived experience from our network

The practical side of low platelets, as our members tell it: soft toothbrushes, electric razors, no contact sports, and pressing on every small cut for longer than feels reasonable. For many, the pinpoint petechiae were the sign that finally explained the mystery bruises.

Worth asking your care team: At what platelet count would we change plans — delay treatment, adjust medicines that affect bleeding, or transfuse?