blood cell count
Meaning of blood cell count: One of the most frequently ordered blood tests, counting three separate cell lines at once and pointing in many different directions.
Definition of blood cell count
A blood cell count is a laboratory test measuring the red cells, white cells and platelets in a sample of blood. Modern analyzers report far more than three numbers, adding the hemoglobin concentration, the proportion of blood occupied by red cells, and the average size and hemoglobin content of those cells. The full panel is usually called a complete blood count.
What do the three cell lines show?
| Cell line | What it does | What a change may mean |
|---|---|---|
| Red cells | Carry oxygen | Low suggests anemia, high suggests dehydration or overproduction |
| White cells | Fight infection | High with infection or inflammation, low after chemotherapy |
| Platelets | Seal damaged vessels | Low brings bruising and bleeding, high may follow inflammation |
What does the differential add?
White cells come in five main types doing quite different work, and a total says nothing about the mix. The differential splits the count into neutrophils, lymphocytes, monocytes, eosinophils and basophils. A high neutrophil figure suggests bacterial infection or a stress response, a high lymphocyte figure points more toward a viral one, and eosinophils rise with allergy and with parasitic infection. The neutrophil number carries particular weight during chemotherapy, since a fall below a certain level leaves someone exposed to infections a healthy immune system handles unnoticed. Where the figures look unusual, a drop of blood is smeared on a slide and examined by eye, which reveals shape and maturity that no automated counter can judge.
What are its limits?
It counts what is circulating at one moment, not what the bone marrow is doing, and the two can differ sharply. Cells may be produced normally and destroyed early, or produced poorly and cleared slowly, and both situations can look identical on the printout. A normal count does not exclude marrow disease, and an abnormal one names no cause by itself. Values shift with hydration, recent exercise, time of day, pregnancy and altitude, so a single result carries less meaning than a trend across several. The test is commonly repeated before and after a blood transfusion to establish what effect it had.
Also known as
Used in a sentence
A blood cell count was repeated before the next cycle of chemotherapy.
Good to know
The count reflects the cells circulating at one moment rather than marrow activity, so a production problem and a destruction problem can generate identical numbers, and hydration alone shifts the values.