When a blood test is done, not only the number of its cells is evaluated, but also their quality. Characteristics such as color, shape, size also matter in the diagnosis of diseases and are sometimes the only pathognomonic symptom of the disease. Therefore, hematologists ask the laboratory to indicate in the analyzes also RDW, which stands for the distribution of red blood cells in magnitude.
What it is?
The basis of our blood, in addition to fluid, is the cells produced by the bone marrow. They come in three types: red, white, and blood platelets. In this case, we are interested in red cells or red blood cells. These are small biconcave discs that give the blood its color, and are also carriers of oxygen from the lungs to tissues and organs. In healthy people, they all have the same shape, color and volume. It is from the last indicator that the correct operation of these cells depends. It is called MCV and normally can fluctuate slightly, this is called the width of the volume distribution.
If the doctor can predict that the patient's cell volume may change, then he directs him to a general blood test. In this case, the laboratory assistant sets himself. This is especially true if anisocytosis is observed in the blood.
What does RDW mean in a blood test? This is the very violation of the distribution of red blood cells in size.
Anisocytosis is a pathological change in the size of red blood cells. Normally, it varies from seven to seven and a half micrometers. Microcytes have a size of up to 6.9 micrometers, and macrocytes, respectively, from eight to twelve micrometers. Larger cells cannot pass along the diameter of the capillary, therefore they are disposed of in the spleen. In a healthy person, the ratio of normal and altered red blood cells ranges from 5: 1. Clinically, anisocytosis is manifested by anemia, heart failure, shortness of breath, cyanosis. The reasons for the development of this condition may be a lack of vitamins, especially B12 and A, lack of iron, impaired red bone marrow, such as myelodysplastic syndrome or the presence of metastases in it with blood cancer. Treatment depends on the cause and comes down to its elimination.
Analysis purpose
Typically, RDW in a blood test is determined in conjunction with other indicators at the initial stage of diagnosis. This study can be prescribed both planned, during the registration of the patient in a medical institution, and urgently, before surgical interventions. In addition, for some group of patients, the determination of RDW is done regularly to monitor the dynamics of treatment for blood diseases.
If the result is positive, the doctor will definitely prescribe a re-examination, since under the influence of external minor factors, a false-positive test for RDW can be diagnosed.
UAC and RDW
Typically, an MCV is also determined in an RDW blood test. This helps to more fully see the picture of the disease and differentiate one or another type of
microcytic anemia. If the MCV is lower than due, with the norm of RDW, then this may be a sign of such severe pathologies as thalassemia, blood transfusion, hemorrhage and many others. In addition, sometimes
neoplastic processes can give such a picture of the blood, especially if the patient has undergone chemotherapeutic treatment.
There may be a reverse situation when the MCV is above the mark, and the RDW is normal again. This combination is noted in liver diseases. But the latter are characterized by a peculiar biochemical picture of blood and a coagulogram, so it will not be difficult for a qualified doctor to conduct differential diagnostics.
Research Methodology
The patient gives blood from a vein on an empty stomach, and for small children and infants there is enough blood from a finger. After the laboratory assistant completes the procedure, he places 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 calculates the number of different types of cells, evaluates them and draws up a conclusion. The results are displayed on 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 almost all of the tests related to the diagnosis of anemia, since the mobility of the blood picture gives the doctor a reason to doubt the correctness of the chosen treatment tactics and revise the methods for correcting this pathological condition.
Normal performance
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 ranges from 11.6 to 18.7 percent. After all, they cannot all be completely identical.
When characterizing the RDW index, remember that this parameter does not depend on the size of the cell itself. This can give false negative results, and is due to the fact that a large number of altered red blood cells are present in the blood. Such red blood cells are called macrocytes. Sometimes, in order to take the analysis results as normal, it is necessary not only to match RDW, but also to correlate it with MCV.
Increased rates
RDW in a blood test may be elevated in several cases. This is usually a sign of anemia, usually iron deficiency. But there is a chance of developing B12-deficient anemia, folate deficiency or liver disease. Therefore, it is necessary to conduct differential diagnostics, prescribe additional examinations and critically approach their results. Determining the type of anemia is a laborious task for a clinician.
Iron-deficiency anemia
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 normal limits, but the level of hemoglobin in them reaches the lower limit or drops significantly. This gives rise to a diagnosis of anemia. But in the blood test, RDW will be normal, as there is still no anisocytosis, and the bone marrow is functioning normally.
The next stage is characterized by an even greater drop in hemoglobin and the number of red blood cells, but now other indicators are also changing. The RDW in the blood test is increased, deviations are observed in the volume of cells, their hemoglobin content and its concentration. The histogram will be strongly shifted to the left.
After the treatment, under the control of the blood composition, the number, volume and form of red blood cells returns to normal. This is achieved by taking iron supplements.
Indicator decline
It is not strange, but if the RDW in the blood test is lowered, then it can also indicate anemia. Therefore, pay attention also to the MCV. Since a decrease in them at the same time may indicate liver disease. Usually more than one analysis is required to understand the reason for such a change in the blood picture as a whole.
In any case, do not sprinkle ash on your head ahead of time. Inaccuracies can be made in a blood test (RDW), as it is made by a machine and manual conversion is necessary. In addition, abnormalities can occur after a blood transfusion or surgery. Then you need to repeat the analysis later.
So you got your blood test. RDW - Upgraded. What does it mean? Most likely, the laboratory assistant did not calibrate the device or you recently had injuries with minor surgical interventions, or you were a donor.
The blood picture changes quite quickly, so do not go into panic. You should show the analysis to your doctor and carefully listen 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 extremely important for making a diagnosis.