Generality
PDW stands for Platelet Distribution Width, which can be Italianized in " platelet distribution width ". This laboratory parameter expresses the degree of variability of the platelet size; consequently, high PDW values indicate a large discrepancy between the volumes of these "cells", whereas when PDW is low it means that the platelets have uniform dimensions.
Given this clinical significance, PDW is known as an index of platelet anisocytosis ; in fact, anisocytosis refers to the presence in the blood of red blood cells of different sizes.
The clinical significance of PDW must necessarily be evaluated together with the other platelet indices, such as the total number (PLT), the mean volume (MPV) and the blood platelet concentration (PCT).
The PDW values can be considered an index of platelet activation, given that the platelet volume tends to increase due to the emission of pseudopodia during the activation of the coagulation processes.
What's this
Platelets (or thrombocytes) are small blood elements, with a discoidal shape and a diameter between 2 and 3 µm, which are fundamental for normal coagulation.
Platelets are produced by the bone marrow and are released into the bloodstream; here, they survive in circulation for about 8-10 days, so the bone marrow must continually produce new elements to replace those that are degraded, consumed and / or lost during bleeding.
The amplitude of distribution of platelet volumes (PDW) is a parameter that indicates how uniform the platelets are in size. Usually, the larger cells are relatively young and more recently released from the bone marrow, while the smaller ones can be older and remain in circulation for a few more days.
When the PDW values are high, it means that there is a big difference between the platelet volumes, while, when the PDW is low, it means that the platelets have uniform dimensions.
Why do you measure
In blood tests, the PDW index corresponds to the degree of variability in platelet size. In other words, the parameter expresses the uniformity or discrepancy in the size of these cells.
The breadth of platelet distribution (PDW) helps to diagnose and / or monitor pathologies in which these hematological cells are not uniform in size, such as haemostatic disorders and myeloproliferative syndromes.
Associated examinations
The measurement of the PDW index must be carried out together with count, mean volume (MPV), one or more platelet function tests and / or other coagulation evaluation tests, such as PT (Prothrombin time) and PTT (Time of Partial Thromboplastin). For example, a high number of large platelets in a person with thrombocytopenia suggests that the bone marrow is producing these cells and releases them into the circulation very quickly.
Normal values
A normal PDW indicates that the platelets are all more or less equal in size.
The reference interval varies from 9 to 14 fl (femtolitro, or one millionth of a billionth of a liter).
However, it should always be considered that this range can change according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the values associated with normality reported directly on the report.
PDW High - Causes
A high PDW indicates that the platelets are quite different from each other. This can signal the presence of a disease that involves these blood cells.
High PDW values may depend, for example, on:
- Myeloproliferative syndromes;
- Megaloblastic anemia;
- Refractory anemia.
PDW Low - Causes
When the PDW is low, it means that the platelets have uniform dimensions. Therefore, reduced values are not associated with medical problems and / or pathological consequences.
How to measure it
The amplitude of distribution of platelet volumes (PDW) is a calculation performed by an automated instrument for haemocytometric analysis. A sample of blood is taken from a vein in the arm, usually in the morning and fasting, which will then be analyzed by the instrument.
In some pathologies, platelets can clump together and appear falsely low in number and / or high in size, so a blood smear is needed to examine the platelets directly under the microscope.
Preparation
To undergo blood sampling, it is necessary to abstain from food and drink for at least 8-10 hours.
Interpretation of Results
The amplitude of distribution of platelet volumes (PDW) indicates the change in platelet size.
- A normal PDW indicates that the platelets are all more or less equal in size;
- A low PDW is related to the high uniformity of platelet size;
- A high PDW indicates some discrepancy in platelet size.
Often, abnormal results require further investigation.
PDW is a particularly useful parameter in distinguishing between reactive thrombocytosis and that associated with a myeloproliferative disorder.
