What should you know about blood test to check bone marrow?

A blood test can show how well your bone marrow is making blood cells, but it cannot examine the marrow directly. A full blood count measures red cells, white cells and platelets. The pattern may suggest reduced production, blood-cell loss or another illness, so your clinician may compare it with earlier results and arrange additional testing.

Red-cell results can point towards anaemia, while white-cell and platelet results provide clues about infection, inflammation or problems affecting blood-cell production. A reticulocyte count shows whether the marrow is responding by releasing young red cells. A blood film lets a laboratory specialist examine cell size, shape and appearance. Abnormal results do not identify one cause on their own. Nutritional deficiency, kidney disease, infection, medication effects and other conditions can alter blood counts. For example, anaemia can occur with coeliac disease or Crohn's disease, and kidney disease can affect red-cell production.

If the pattern remains unexplained, a clinician may discuss tests such as iron, vitamin B12, folate, kidney-function and inflammation tests. A bone-marrow aspiration or biopsy is a separate procedure that collects marrow for direct examination; it is considered only when the blood results and clinical history make it useful.

Follow the instructions from the clinic. Many full blood counts do not require fasting, but fasting may be needed if other tests are taken at the same appointment. Tell the clinician about medicines, supplements, recent infections, bleeding, heavy periods and symptoms such as tiredness or repeated infections. Do not stop a prescribed medicine unless the prescriber tells you to. After the sample, keep pressure on the area for several minutes and mention persistent bleeding, increasing swelling or worsening pain. Ask when the result will be reviewed and whether a repeat sample or another test is planned.

Arrange prompt medical advice for unexplained or worsening breathlessness, marked weakness, fainting, new widespread bruising, bleeding that is difficult to stop, or repeated infections with fever. Seek emergency help for severe breathing difficulty, collapse, confusion, or heavy bleeding. These symptoms need assessment because they may reflect a significant problem with oxygen-carrying cells, clotting cells or infection defence; they should not be judged from a blood-count result alone.

Useful questions include: Which blood-cell result is outside the expected range? Does the pattern suggest reduced production or another explanation? Do I need a blood film, reticulocyte count or nutritional tests? Could my medicines or a recent illness affect the result? When should the result be repeated, and what symptoms should lead me to seek earlier care?