What Is The Packed Cell Volume (PCV) Test?
Also known as the haematocrit test, the PCV or Packed Cell Volume Test is a test done to diagnose polycythaemia, dehydration or anaemia in certain patients. It is generally a part of the full blood count test that is used to estimate the need for certain blood transfusions and monitor the response to treatment. Blood, in general, is a mix of plasma as well as cells.
The PCV test measures how much of the blood consists of cells. If the PCV returns a reading of 50%, it means that 50 ml of the cells are present in exactly 100 ml of blood. If the RBC number increases, then the total reading of the PCV is also up. This number can also increase due to dehydration.
Performing the PCV tests and the total solids is a pretty routine and simple test undertaken at many hospitals. All medical members can easily perform the test but interpreting them is the tricky part. The readings can provide a lot of information regarding the patient's status and also help plan the next treatment step.
A lower number of the PCV means that the RBC count loss is due to reasons such as blood loss, cell destruction and less bone marrow production. Increased PCV can generally mean that a person is dehydrated and there is a higher number of RBC production
By looking at the tube out of the centrifuge, you can get an idea of the WBC content as well. This buffy coat normally lies between the plasma and red cell layer. (This shouldn't be counted as a part of the PCV test).
The layer of plasma should also be examined for lipemia, hemolysis in addition to icterus.
Preparation For The Pcv Test:
There isn't any special preparation required for the PCV test. If you are anxious about the test, it is better to talk to the doctor and let him/her know. Also, any medications that you've been taking have to be relayed to the doctor. If there are any medical problems which are underlying too, you need to fast before taking a test.
Uses Of Packed Cell Volume Test
A low PCV implies that the patient has a low number of red blood cells and is suffering from anaemia. The doctor may ask the patient to undergo further tests to determine the underlying causes of anaemia. Treatment will be given accordingly.
Measuring The Pcv Test:
The PCV test is calculated with the help of an automated analyser which means that it isn't directly measured. By multiplying the red cell count with the mean cell volume, doctors get the final amount. PCV is slightly less accurate than the hematocrit as they include small amounts of the plasma from the blood that is generally trapped in between two red cells.
By tripling the haemoglobin concentration and dropping the units, an estimated hematocrit can be determined in percentage.
The PCV can also be determined with the help of the of a capillary tube and the centrifuging heparinised blood in it at around 10000 RPM for roughly five minutes. This process helped in separating the blood into different layers, and the volume of the total packed RBC divided by the blood sample's total volume gives the final amount of the PCV.
Since a tube is also used, it can be used to measure the lengths lying between certain layers.
There is also another way to measure the levels of hematocrit, and this is through optical methods such as spectrophotometry. With the help of differentials, the differences between the optical densities of the sample flowing through the glass tubes at isosbestic wavelengths and the product containing the luminal diameter along with the hematocrit can create a linear relationship.
When Does A Low Pcv Reading Occur?
There are certain conditions that contribute to the low reading in the PCV. These include:
- Nutritional deficiencies of iron or vitamin (B12 or folate) and mineral deficiencies
- Inflammatory conditions, for example, rheumatoid arthritis
- Kidney diseases
- Haemolysis, which is the situation where the RBCs are destroyed prematurely by the immune system. This occurs due to certain organ damages and inherited abnormalities of the RBCs
- Liver cirrhosis
- Medicines - including that of chemotherapy
- Abnormalities of RBCs or haemoglobin containing disorders such as myelodysplastic syndrome, lymphoma, bone marrow disorders and myeloma
One of the most common causes of heightened PCV readings is that of dehydration. With adequate fluid intake, the levels return to normal, but it can also create a condition known as polycythaemia where there are more RBCs