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RDW test

A red cell distribution width, shortened as RDW, is a blood test that measures the amount of red blood cell variation in size and volume. Red blood cells help carry oxygen from the lungs to other body parts. Any value outside the normal range in red blood cell volume or width signifies a potential problem with the body’s function that may affect oxygen distribution to different body parts.

However, some diseases may occur, and the RDW will remain normal. Normal red blood cells have a standard diameter of 6 – 8 micrometres (µm). If your result is higher than this range, your RDW is elevated.

If your average RBCs are small and you have many small cells, you will have an elevated RDW. If, on average, your RBCs are large and you have many large cells, your RDW will also be elevated.

Your doctor cannot use only the RDW parameter when interpreting your complete blood count (CBC). Th RDW tests help with other tests, such as mean corpuscular value (MCV) and haemoglobin (hgb), to get detailed information on your red blood cell count.

High RDW values may indicate a nutrient deficiency, anaemia or other conditions.

Why is the RDW test necessary?

The RDW test helps to diagnose different types of anaemia and other medical condition, such as

The RDW test is usually a part of the complete blood count (CBC). A CBC checks the types and number of blood cells and other blood parameters such as platelets, red blood cells and white blood cells.

CBC can also check your overall health and may also diagnose infection and other diseases.

Your doctor may check your RDW test during a CBC if you have

Preparing for an RDW test

Before an RDW blood test, you may need to fast, depending on the other tests your doctor wants you to have. The doctor may also give you special instructions before the test.

The blood collection test takes less than five minutes and involves your healthcare provider taking a blood sample from a vein into a test tube. When your provider has drawn enough blood samples, they will remove the needle and apply pressure, then place a small bandage on the site to stop bleeding. The healthcare professional will send the blood sample to the lab for analysis.

If the spot your provider inserted the needle continues bleeding for several hours, visit your doctor immediately.

Interpretation of RDW result

The normal RDW range in adult males is 11.8 – 14.5% and 12.2 – 16.1% in adult females. If your RDW value is outside this range, you may have an infection, nutrient deficiency or other disorders.

For an accurate diagnosis, your doctor may order or check other blood tests like the mean corpuscular volume (MCV) test, which is also a part of the CBC. This will ensure getting the right recommendations and treatment.

Besides helping to confirm a diagnosis, the RDW results and other tests can also determine the type of anaemia.

High results

A high RDW may indicate a nutrient deficiency, such as folate, vitamin B12 and iron. It may also mean you have macrocytic anaemia, where your body doesn’t produce sufficient normal red blood cells, and the other cells produced are larger than normal. This may be due to folate or vitamin B12 deficiency.

You can also have microcytic anaemia, a deficiency where your red blood cells are smaller than normal. Iron deficiency anaemia can cause microcytic anaemia.

For a proper diagnosis, your healthcare provider will perform a CBC test and compare your MCV and RDW results to measure your red blood cell volume.

A high MCV and RDW may be present in some macrocytic anaemias, while a high RDW and low MCV occur in people with microcytic anaemia.

Low results

A low RDW result is not associated with any haematologic disorders.

Normal results

If your RDW is normal with a low MCV, you may have anaemia resulting from a chronic disease such as chronic kidney disease. You may have aplastic anaemia if you have a high MCV, but your RDW is normal. Aplastic anaemia is a blood disorder where the bone marrow doesn’t produce sufficient blood cells, including red blood cells.

If you need an RDW test to confirm your test result for blood disorders, visit our Clinic at Suite E, 117a Harley St, Marylebone, London, W1G 6AT. You can also call us on 02071830244 to schedule an appointment for y our RDW test and other blood tests.