Accuracy of Coulter S PCV is influenced by calibration of the instrument which may not be set correctly and by incorrect dilution of the specimen for counting References Praful B.
Godkar, Darshan P. Textbook of medical laboratory technology A high hematocrit may reflect an absolute increase in the number of erythrocytes, or a decrease in plasma volume, in conditions such as [3]:. High hematocrit is also used as an indicator of the excessive intake of exogenous erythropoitin EPO , which stimulates the production of red blood cells. Athletes can artificially improve their performance by enhancing the oxygen-carrying capacity with EPO. In newborns and especially premature babies, high hematocrit values are common.
The hematocrit of infants reaches the level of adult hematocrit by approx. The conditions leading to low hematocrit values, e. If the hematocrit is measured immediately after an acute hemorrhage, the value will be normal until the decreased blood volume is corrected by fluid shifts into the blood vessels. This section gives a technical description of the most commonly used techniques for measuring hematocrit:. Method [4]: Hematocrit PCV is the measure of the ratio of the volume occupied by the red blood cells to the volume of whole blood.
The blood sample is drawn into a capillary and centrifugated, and then the ratio can be measured and expressed as a decimal or percentage fraction. In hematology laboratories, automatic cell count analyzers measuring multiple parameters are the most commonly used.
Method: The hematocrit is determined indirectly from the average size and number of RBCs. The reference method is the Coulter impedance principle [6] and is described below.
Some blood gas analyzers determine hematocrit by a conductivity measurement which is corrected for the concentrations of conducting ions in the sample. Three factors besides the number of RBCs are critical for the determination of the hematocrit value when using a method based on measurement of electrical conductivity:. As there is a linear relationship between hemoglobin c tHb and hematocrit as described earlier, it is possible to calculate the hematocrit on analyzers that measure hemoglobin.
When making this conversion, two factors should be taken into consideration:. The measurement of c tHb from most good-quality analyzers is usually reliable; however, the equations used to calculate the hematocrit vary from analyzer to analyzer. Some analyzers use an empirically found equation [2,13] whereas others use an approximate conversion factor of 3 [14,15]. All measuring technologies for determining hematocrit have advantages and disadvantages. The following table provides an easy overview of the described methods.
Time-consuming and careful preparation required sealing of capillaries, etc. Leakage of sealing gives falsely low results more RBCs will be lost than plasma [5]. Falsely high Hct readings caused by trapped plasma. In normal blood 1. In blood with abnormally sized or shaped RBCs, more plasma will be trapped, causing a higher positive bias of Hct. Clots will lead to false packing of the cells, giving falsely high results [5]. Hemolysis will destroy the cell walls and lead to false packing of the cells, giving falsely low results [5].
Acute hyperosmotic conditions will change the cell volume and lead to a false packing of the cells, giving falsely low results [9]. Elevated reticulocyte or WBC count results in falsely high hematocrit values because these cells will be counted as RBCs [7]. Autoagglutination, where two or more cells are counted as one, will lead to falsely low results [7].
Hemolysis will destroy the cell walls, giving falsely low results [7]. In patients with abnormal osmolality, the addition of an isotonic solution may increase the MCV, leading to falsely elevated Hct readings. Careful sample handling is required, especially careful sample mixing, to avoid false readings.
Acute hyperosmotic conditions will lead to cell shrinkage as water moves out of the cells to equalize the osmotic pressure. This will result in falsely low results similar to the microhematocrit method [9]. Variations in protein concentration in plasma, e. Some analyzers offer correction for this bias [10,11,12].
Attention must be paid to sample handling, specifically proper mixing of the sample, to avoid false readings. Deviation of MCHC from the standard value, e.
Inadequate hemolyzation or mixing of the sample will falsely decrease the hemoglobin [22]. When hematocrit is used to assess anemia and the oxygen-carrying capacity, the advantages and disadvantages of each method must be carefully considered. In addition, the specific clinical and analytical needs for any patient population must be determined. Hematocrit is traditionally a routine hematology laboratory parameter; however, measuring hematocrit as a STAT parameter in a POC setting is in many ways preferable, as this will save time in critical situations and avoid specimen transport problems.
Some blood gas analyzers offer this possibility, either by measuring hematocrit by conductivity or by calculating hematocrit from c tHb. Different hemoglobin measuring methods and their applications will be discussed in another article. Both POCT and traditional laboratory methods of measuring or calculating hematocrit have limitations. Methods used outside of the laboratory must be intuitive for users without time-consuming sample handling.
Methods suitable for an adult environment may not be suitable for a neonatal environment due to sample volume limitations. Some methods are not suitable in certain applications due to e. These limitations can have important clinical implications and must be carefully considered as described in this article. Radiometer and acutecaretesting. Printed from acutecaretesting. September Hematocrit - a review of different analytical methods.
Microhematocrit 2. Complete blood cell count 3. Conductivity on blood gas analyzers 4. Calculation of hematocrit Comparison of the different technologies This article will be followed by another article describing the different methods of determining hemoglobin. We can help. I understand that this will override the DND status on my mobile number. 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. 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.
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. There isn't any special preparation required for the PCV test. 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.
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