The Red Distribution Width (RDW) is a measurement of the dispersion of red blood cells in a sample. It is INDEED THE COEFFICIENT OF VARIATION of the red blood cells in the sample (standard error/mean*100).

Large values implies that there could be several clones of RBC circulating. For example in a vitamins B12, B9 (also known as folate) or iron deficiency, as well as bleeding, the volume of the cell (known as "mean corpuscular volume" or MCV) changes: in the case of vitamins B12, B9 and bleeding increases MCV and they iron deficiency decrease it.

Since in all of this cases, old RBC's coexist with new abnormal ones, the RDW increases. Treatment of those diseases increase even more the value of RDW. But as the abnormal clones disappear, the RDW decreases again.

The humble wikipedia can illustrate you:

http://en.wikipedia.org/wiki/RDW

and

http://en.wikipedia.org/wiki/Mean_corpuscular_volume

I fail hematology, but after the second time, I've learned a lot of! However, I don't use it in my daily life.

:(

Thank you for your answer Hedley, and sorry to hear that you failed your hematology exam! We often learn from our failures. Unlike you, I feel that hematology is an important science. Your answer was helpful, but I wouldn't rely on Wikipedia completely. Do you think that there is a certain range that should not be exceeded for the RDW to be considered normal? And if that range is exceeded, what should we do next?

There are two reports of RDW and RDW-CV . Both should not exceed their normal values. if they are and there is fall in Hb from previous values one should investigate accordingly. Also RDW indicates aniscytosis. It may be altered in Hemoglobinopathies a well.

In relation to the original question ' Can it be used with any significance in relation to anemia?

I would suggest so. In observing the RDW and the red cell plots showing this value, the level of response to the treatment of anaemia within that patient can be assessed. A good response to iron therapy can give a high RDW >20 and a clear double-peak can be observed. A poor response to treatment will have a small / negligable change in RDW from the norm.

The RDW is usually abnormal in iron deficiency anaemia but less commonly abnormal in thalassaemia trait. It is in fact one of the many features used to help differentiate the two.

Thank you Beverely. So, are you saying that the higher the RDW the better is the prognosis for anemic patients?

Thank you David. What do you mean by "abnormal"? High or low?

Hi Najla, if there is a higher RDW with a clear double peak that person has shown a good response to iron therapy.

Usually higher in >90%of IDA, but only in ~50% of thalassaemia traits. Used together with other indices such as RCC, it is very helpful in differentiating the two.

Many thanks for both of you Beverley and David. I understood from your answers that RDW is higher in IDA and it gets higher if there is a good response to treatment. Is this right?

I would suggest that a return to 'normal' RDW is more suggestive of a successful response to therapy, as it means the red cells have become more uniform again, and less variable in size. The RDW will increase with either an increase in larger cells, small cells, or both. It is an indicator of size variation, a more objective assessment of anisocytosis.

If I can add my 2 cents.

I wouldn't say "clone" because I don't consider these red blood cells as clones.

Then I think it is important to keep in mind that RDW is absolutely not sensitive and you'll probably will have no problem in identifying anisocytosis on your smear before the RDW increases.

RDW  directly indicates Anisocytosis among RBCs population.Whenever there is a variation in morphology  the RDW increases.It is increased in IDA, IDA under Fe treatment, hemoytic anemias, sickle cells disease, thalassemia etc, Also note that abnormal signal signs or noise within the cell counter or nearby area may produce erraneus results of RDW. RDW is surely an important parameter in the CBC, but one cannot fully depend  on that alone!! Moreover , there are different diagnostic methods to differentiate  the above cases.

RDW is usually high in iron deficiency anaemia but normal or near normal in thalassaemia, helping to differentiate between the two conditions.  If one uses this together with the MCV to RCC ratio, one can easily distinguish between the two conditions.

Studies on the clinical use of CBC have increased in recent years. CBC in psychiatric respect, it is an easy and inexpensive method to utilize hematologic parameters in cases where we cannot get clear information from the patients. RDW is a parameter of complete blood count (CBC) and investigated recently in different situations. We have investigated in our different studies and demonstrated such issues as follow:

1. According to the comparison of CBC values, RDW_CV (%) was significantly higher (p = 0.026*) in the opioid use disorder (OUD) group (n=61) compared to the healthy control group (n=61).

2. We have found that RDW_CV (%) value was 12.09 ± 2.00 in violent suicide attempt group (VSA); 12.44 ± 1.50 in non-violent suicide attempt group (NVSA); 12.27 ± 1.99 (0.747) in healthy control group. Our study suggests that there is a relationship between hematological parameters and OUD, especially the immune cells. There was no change in parameters associated with RBCs except RDW_CV. This result, which is not significant, is similar to some statements in the literature, but incompatible with some. Rasheed and Iqtidar (1) investigated the hematologic parameters of 100 heroin dependents and suggested a statistically significant decrease in HGB, HTC, RBC count, and platelets count in heroin addicts as compared to control subjects. Verde Méndez (2) demonstrated that for both sexes, the levels of HTC and HGB were similar in the control groups and opiate addicts.

References:

1. Rasheed, A.; Iqtidar, A. Hematological Profile, Serum Electrolytes and Iron Level Investigations in Heroin Addicts. Acta. Pharmaceutica. Turcica. 1997, XXXIX(2), 59–63.

23. Verde Méndez, C. M.; Díaz-Flores, J. F.; Sañudo, R. I.; Rodríguez Rodríguez, E. M.; Díaz Romero, C. Haematologic Parameters in Opiate Addicts. Nutr. Hosp. 2003, 18(6), 358–365.

That is interesting! Thanks @ Mehmet Hamdi Örüm

RDW is useful when it is high, it means there is anisocytosis of RBCs so maybe there is macrocytosis or microcytosis but the MCV is in normal range so we have to examine the peripheral blood smear for observe RBCs.