What is Red blood cell distribution width (RDW)
The RDW blood test is a quantitative analysis of variance in red blood cells (RBC) width where RDW stands for red blood cell distribution width or RCDW. It is also apart of the complete blood count (CBC) test. If the test shows high results, it implies that the person may be suffering from iron deficiency or may be having anemia. RDW test results are mostly used along with the mean corpuscular volume (MCV) to determine if one is suffering from anemia. The red blood cells size are in the range of 6-8μm for a normal person. Any variation in this suggests that the person is suffering from disorders. The normal range for RDW results is 11 to 15%, variations from this implies that there is something wrong. When the results suggest anemia, on conducting further investigation the exact cause can be found. In such scenarios, the practitioner suggests corpuscular volume test.
Conducting the RDW blood test
Conducting the RDW test requires a blood sample. It would be collected from a vein either near the inside elbow or back of the hand. For taking the sample for infants and young children, they poke with a needle in the finger or heel. One can get these tests done as a part of the complete blood test, which can be done at most laboratories. In such scenarios, the white blood cell count is also associated with it. It is extremely crucial that people understand the requirement of the test as they grow older. Research shows that high RDW rates are fatal to people over the age of 45. Thus, it is advisable that they get the RDW tested regularly on a yearly basis to avoid any risk factors.
Why the Test is Performed
With RDW blood analysis one can determine, if the cause for anemia is multiple or a single cause. Vitamin B12 deficiency indicates normal RDW but manifests in the blood as large cell anemia, whereas iron deficiency has a high RDW and variation in size of red blood cells. When a person has both vitamin B12 and iron deficiencies, they will have both small and large cells which drastically elevates the final results of the RDW blood test. Anisocytosis is the situation of the patient with varying sizes of cells. With RDW value, one can determine diseases such as cancer, cardiovascular disorders, anemia, thalassemia and malnutrition. Apart from this, one has to understand that there are more than 400 types of anemia which have to be tested further to deduce the exact illness.
Calculating the RDW Value
To calculate the RDW value, divide standard deviation of MCV by mean MCV and multiply with 100. Standard deviation in this case is the red blood cells number present in the blood smear. RDW is not the width of the red blood cells but the width of the volume or the distribution.
RDW = (Standard deviation of MCV ÷ mean MCV) × 100.
MCV and RDW
MCV (mean corpuscular volume) and RDW (red blood cell distribution width) together determine the disease the patient is suffering. When both values are high, it might be folate deficiency, Pre-leukemia associates with high MCV and normal RDW and Normal MCV and high RDW signifies B12 deficiency. When both are normal or if MCV is low and RDW is normal it might be a chronic disease, and when both are low it is iron deficiency. In some extreme cases, RDW count is the predicament of mortality, which is in cases of cardiovascular disease problems and cancer. Higher rates are more dangerous than the lower levels.