When a blood test is done, not only the quantity of its cells is evaluated, but also their quality. Such characteristics as color, shape, size, too, are important in the diagnosis of diseases and are sometimes the only pathognomonic symptom of the disease. Therefore, hematologists are asked in the laboratory to indicate in the analyzes also RDW, which is deciphered, as the distribution of red blood cells in size.
What it is?
The basis of our blood, in addition to fluid, is the cells produced by the bone marrow. They are of three types: red, white and blood platelets. In this case, we are interested in red cells or erythrocytes. These are small disks of biconcave form that give blood its color, as well as carriers of oxygen from the lungs to tissues and organs. In healthy people, they all have the same shape, color and volume. The correct performance of these cells depends on the last parameter. It is called MCV and can normally fluctuate slightly, this is called the width of the distribution by volume.
If the doctor can predict that the patient's cell volume may change, then he directs it to a general blood test. RDW at the same time the lab operator exposes himself. This is especially true if there is anisocytosis in the blood.
What does RDW mean in blood tests? This is the very violation of the distribution of red blood cells in size.
Anisocytosis is a pathological change in the size of erythrocytes. Normally, it varies from seven to seven and a half micrometers. Microcysts have a value of up to 6.9 micrometers, and macrocytes, respectively, from eight to twelve micrometers. Cells of a larger size can not pass through the diameter of the capillary, so they are disposed of in the spleen. In a healthy person, the ratio of normal and altered erythrocytes varies between 5: 1. Clinically anisocytosis is manifested by anemia, heart failure, dyspnea, cyanosis. The reasons for the development of this condition may be a lack of vitamins, especially B12 and A, lack of iron, disruption of the red bone marrow, such as myelodysplastic syndrome or the presence of metastases in it with blood cancer. Treatment depends on the cause and is reduced to its elimination.
Assignment of analysis
Usually RDW in a blood test is determined together with other indicators at the initial stage of the diagnosis. This study can be scheduled as planned, during the patient's registration in a medical institution, and urgently, before surgical interventions. In addition, some patients with the definition of RDW do regularly, to track the dynamics of treatment for blood diseases.
If the result is positive, the doctor will necessarily appoint a second trial, since under the influence of external minor factors a false positive test can be diagnosed on RDW.
Typically, in the analysis of blood RDW is determined and the indicator MCV. This helps to more fully see the picture of the disease and differentiate this or that type of microcytic anemia. If the MCV score is lower than expected, with the norm of RDW, then this may be a sign of such severe pathologies as thalassemia, hemotransfusion, hemorrhage and many others. In addition, sometimes neoplastic processes can give such a picture of blood, especially if the patient underwent chemotherapy treatment.
There may be a reverse situation, when MCV is higher than the prescribed mark, and RDW is again normal. This combination is noted for liver diseases. But the latter is characterized by a peculiar biochemical picture of blood and coagulogram, so that it is not difficult to carry out differential diagnostics for a qualified doctor.
The patient gives blood from a vein on an empty stomach, and for small children and babies enough blood from a finger is enough. After the lab technician has finished the procedure, he puts the samples in a centrifuge to separate the liquid part of the blood from the cells. After that, he places the resulting dry residue in the analyzer, and the device itself counts the number of different types of cells, evaluates them and makes a conclusion. The results are output to the printer as a histogram.
If the analysis is positive, then according to the protocol it is supposed to be repeated in order to avoid a false positive result. This rule applies to virtually all tests performed related to the diagnosis of anemia, since the motility of the blood picture gives the doctor an occasion to question the correctness of the chosen treatment tactics and to review the methods for correcting this pathological condition.
In the blood test for RDW, a threshold of 11.5-14.5 percent is given for the normal change in the size of red blood cells in adults. In children, this parameter varies in the range from 11.6 to 18.7 percent. After all, they can not all be exactly the same.
When giving an indication of the RDW index, one must remember that this parameter does not depend on the size of the cell itself. This can give false-negative results, and is associated with the fact that a large number of red blood cells are present in the blood. Such red blood cells are called macro-cells. Sometimes, in order to accept the results of the analysis as the norm, it is necessary not only to match RDW, but also to correlate it with MCV.
RDW in the blood test may be elevated in several cases. Usually it is a sign of anemia, usually iron deficiency. But there is a possibility of developing B12-deficient anemia, folate deficiency or liver disease. Therefore, it is necessary to conduct differential diagnosis, assign additional examinations and critically approach their results. To determine the type of anemia is a time-consuming task for a clinician.
Since iron deficiency anemia is the most common in our hemisphere, we will dwell on it in more detail.
At the first stage of the disease, the number of formed elements is within the normal range, but the level of hemoglobin in them reaches the lower limit or falls strongly. This gives reason to diagnose anemia. But in the blood test, RDW will be normal, as there is no anisocytosis yet, and the bone marrow functions normally.
The next stage is characterized by an even greater drop in hemoglobin and the number of red blood cells, but other indicators are now changing. RDW in the blood test is increased, there are deviations in the volume of cells, the content of hemoglobin in them and its concentration. The histogram will be strongly shifted to the left.
After the treatment, under the control of blood composition, the amount, volume and shape of red blood cells comes back to normal. This is achieved by taking iron preparations.
Decrease in the indicator
As it is not strange, but if RDW in the blood test is lowered, then this also may indicate anemia. Therefore pay attention also to the MCV. Since reducing them at the same time may indicate liver disease. It usually takes more than one analysis to understand the cause of this change in the blood picture as a whole.
In any case, do not sprinkle the head with ashes ahead of time. In the analysis of blood (RDW), inaccuracies can be allowed, since the machine makes it and it is necessary to recalculate manually. In addition, abnormalities can occur after a blood transfusion or surgical intervention. Then you need to repeat the analysis later.
Here you have your blood test. RDW - upgraded. What does it mean? Most likely, the fact that the lab technician did not calibrate the device or you recently had trauma with minor surgical interventions, or you were a donor.
The picture of the blood changes quickly enough, so do not panic. It is necessary to show the analysis to your attending physician and listen carefully to his recommendations. This will help to avoid misunderstandings in the future. In addition, each laboratory has its own indicators in the blood test - RDW, depending on what equipment they use. The doctor can refer you to that diagnostic center, the results of which he trusts. This is also very important for the diagnosis.