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RDW is a test of the content of red blood cells in the patient’s blood, taking into account the volume of each group of blood cells. Erythrocytes vary in size, and the RDW test is designed to catch variations in the difference between them. The result is given as a percentage. Going outside the norm can mean anemia (or anemia). What are the WFD standards and what does an incorrect indicator level indicate?
The RDW indicator informs about the range of the blood cell volume range. Therefore, it shows how much different erythrocytes are in the patient’s blood. This is an authoritative way to define variations in the red blood cell population, which are the most important building blocks, responsible for, among other things, rebuilding tissues and sealing wounds. The phenomenon of erythrocyte size variability is termed anisocytosis.
Information on the volume of red blood cells can be determined with the standard deviation index RDW-SD (the measurement uses the FL unit – femtoliters) or the variability RDW CV (expressed as a percentage). The RDW-CV ratio is compared to the mean erythrocyte volume, i.e. MCV.
On the basis of the WFD, the levels of vitamin B12, iron and folic acid can be determined, among others. Higher RDW value usually indicates their shortages. Each laboratory has its own standards, so you should always refer to the unit ranges shown on the test results printout.
To be reliable, combine the red blood cell test with other tests, including hemoglobin levels, MCV levels, and red blood cell counts. The analysis is performed by a doctor on the basis of the results of peripheral blood counts, which takes into account the measurements of the above-mentioned indicators.
Usually, this examination is recommended to be performed with other morphological tests when anemia is suspected or to determine the causes of any kind of anemia. There can be several reasons for this type of disorder. Their correct diagnosis guarantees appropriate treatment, leading to the improvement of the patient’s health.
Designation of the RDW is performed during a basic blood count. Thanks to this, we will receive information about the different volume of erythrocytes during routine control tests. Prophylactic morphology should be performed at least once a year. However, if we observe bothersome symptoms, including fatigue, lethargy, shortness of breath or headaches, we should go to a doctor’s consultation. Based on your symptoms, your doctor should refer you for a morphology. If he does not, you can go to the test privately. Usually, they can be made on the spot, and the price should not be higher than a dozen or so zlotys. You have to go to the doctor’s office with the results.
Trying to understand the test results on your own may raise unnecessary doubts. Occasionally, one of the indicators is outside the norm, but it may not be clinically meaningful if the other values are normal. An experienced physician should make a final evaluation.
- Read more: Morphology – when is it worth doing?
RDW – standard
The variance in the RDW-SD study is given in femtoliters (abbreviation: fl). Usually the norm is 36–47 fl, but in men it may be slightly lower. If the value is expressed as a percentage, it fluctuates around 11,5-14,5 percent. and is then called the RDW-CV indicator. The standards are not uniform and there may be differences between them depending on the laboratory performing the test. This is why going with WFD results to a doctor who will be able to assess the patient’s health on the basis of them.
Do you need interpretation of test results? Are you worried about your symptoms? Contact your doctor. Make an online teleconsultation with your family doctor at haloDoctor.pl to get answers to your questions.
In the assessment of abnormalities associated with red blood cells, not only RDW indicators are important, but also hematocrit (HCT), hemoglobin concentration, MCH, MCHC and the number of reticulocytes.
WFD study – preparation and course
The WFD test is an element of the morphology, therefore its preparation does not differ from typical indications before a regular blood sampling.
- It is important that the patient presents for the test on an empty stomach – this is one of the requirements for the RDW test to be meaningful.
- Physical activity on the day of the test is not advised as it may lead to an increase in red blood cells and may interfere with the results. Intensive effort should also be limited to three days before collection.
- In order to obtain reliable results, you should give up alcohol a few days before the RDW test, and do not smoke cigarettes immediately before donating blood.
- The collection of a blood sample (usually approx. 5 ml) usually takes place in the morning hours in order to be able to compare the results in a daily cycle. The source of the material can be the ulnar vein, but also an ear lobe or a finger.
- It is important that the patient remains in the medical facility for a while after collection in case of problems caused by blood loss (in case of fainting).
The indicative WFD standards are 36–47 fl for RDW-SD and 11,5–14,5 percent. for RDW-CV.
Increased level of the WFD indicator
A high level of the RDW index (above 15%) means that the patient has red blood cells in the blood that are larger than the standard size. One reason could be a vitamin B12, folate, or iron deficiency. Increased index may also occur in people with chronic inflammation. Other possible causes include: blood transfusion, a history of haemorrhage, bone tumor metastasis.
It is useful to compare the RDW with the MCV index in determining the correct cause of anemia. An elevated RDW with a low MCV is most likely an iron deficiency, while a high MCV is a vitamin B12 or folate deficiency in the body. Overstimulation of red blood cell production may be a consequence of blood loss, so women undergoing monthly bleeding are at risk of false-positive test results.
With a high level of the WFD index, it is worth learning about thalassemia (thyroid cell anemia) and liver insufficiency.
Low RDW rate
Reduction in red blood cell volume is most often associated with anemia, as this disease shows a disorder of the bone marrow hematopoiesis. A low index can also be caused by leukemia, body failure or iron deficiency. The rate is below 10,2 percent. may be macrocytic anemia. In this case, the body produces few red cells, but all of them are large, so the difference between their volume is small – the WFD index is therefore low. This result could also be a symptom of microcytic anemia, when the red blood cells produced are very small.
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During interpretation of the erythrocyte span the doctor familiarizes himself with the general morphology, carries out a physical examination of the patient and takes into account his health, age and lifestyle. Therefore, one should look for deviations co-occurring in the results with respect to the standards in force in given laboratories. Before performing the analysis, you should usually familiarize your doctor with any past injuries, as an increase in the number of red blood cells or variations in their size may be due to recent blood loss, transfusions or varicose veins inside the body.