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.
Low hematocrit A low hematocrit reflects a low number of circulating red blood cells and is an indicator of a decrease in the oxygen-carrying capacity or of overhydration. Examples of conditions causing a low hematocrit anemia include [3]: Internal or external hemorrhage — bleeding Complication of chronic renal failure — kidney disease Pernicious anemia — vitamin-B12 deficiency Hemolysis — associated with transfusion reactions A low hematocrit may be found in autoimmune diseases and bone-marrow failures.
High hematocrit A high hematocrit may reflect an absolute increase in the number of erythrocytes, or a decrease in plasma volume, in conditions such as [3]: Severe dehydration — e. A minimum of two capillaries is required to ensure balance in the centrifuge. It is important that the tubes are sealed thoroughly. After five minutes of centrifugation the hematocrit can be measured while the tubes are still kept in a horizontal position.
A distinct column of packed erythrocytes is visible in one end of the capillary tube Fig. The packed erythrocytes are followed by first a small turbid layer — the buffy coat layer — and then a clear column of plasma Fig.
Hematocrit is estimated by calculating the ratio of the column of packed erythrocytes to the total length of the sample in the capillary tube, measured with a graphic reading device. The measurement should be performed within 10 minutes to avoid merging of the layers.
Reading the hematocrit Limitations: Studies have shown that spun hematocrit gives values approx. If abnormal types of RBCs are present, this bias can be even greater, as more plasma is trapped [5]. See also Table I. Complete blood cell count CBC In hematology laboratories, automatic cell count analyzers measuring multiple parameters are the most commonly used. Materials: Sample tubes normally containing mL EDTA anticoagulated blood Procedure: The whole-blood sample is diluted automatically with an isotonic solution prior to analysis.
The diluted blood is forced through an orifice which has two electrodes placed on opposite sides Fig. By applying a constant current between the two electrodes, the impedance is constant until a blood cell passes through the orifice Due to the non-conductive properties of the red blood cell membrane, the electrical resistance increases each time an erythrocyte passes through the orifice.
The change in potential between the electrodes correlates to the volume of the passing erythrocyte. Furthermore, erythrocytes that have passed through the orifice are counted. From the mean cell volume, the erythrocyte count and the dilution factor, the hematocrit is derived.
The Coulter principle Limitations: When a high reticulocyte or WBC count is present, hematocrit determinations using hematology analyzers can result in the calculation of falsely elevated values, because the higher cell volumes of these cells will interfere with the red blood cell count and the calculation of the hematocrit [7].
Materials: Syringes or capillaries containing heparinized arterial or venous blood Method: The conductivity is the ability of a solution to transmit conduct electricity. The electrical current will increase in proportion to the number of ions or charged particles found in a solution, their electrical charge and mobility, i.
The mobility of an ion in a solution will also depend on how many cells and size and shape are suspended in the solution. Both erythrocytes and plasma have characteristic electrophysical properties.
Hematocrit results are reported as a percentage. According to the Cleveland clinic, the general normal ranges for hematocrit are [4] :.
If your hematocrit is high, it means that you have more red blood cells than is considered healthy. High hematocrit may be caused by [] :. A false high hematocrit may be reported if the patient has cryoproteins, significant leukocytosis, or giant platelets. If your hematocrit is low, it means that you have fewer red blood cells than is considered healthy.
Low hematocrit may be caused by [] :. A false low hematocrit may be reported if the patient has microcytosis, in vitro hemolysis, or autoagglutinins. In some cases, hematocrit is caused because of low iron levels. You can eat iron-rich foods and take a daily vitamin supplement to help prevent low hematocrit causes. Food sources that are rich in iron include:.
Additionally, vitamin C helps with iron absorption. Therefore, also eat various foods that are rich in vitamin C, for example, citrus fruits. Do not drink coffee or tea with your meals because this decreases iron absorption. Mondal H, Budh D. Published online May 9, Talk to your doctor about what your hematocrit test result means in light of the symptoms you're experiencing and the results of other diagnostic tests.
A number of factors can affect the outcome of a hematocrit test and yield inaccurate or misleading results, including:.
Your doctor will take into account possible complicating factors when interpreting the results of your hematocrit test. Your doctor may want to repeat the hematocrit test and do other blood tests if results provide conflicting or unexpected information. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version.
Sections for Hematocrit test About. Overview A hematocrit he-MAT-uh-krit test measures the proportion of red blood cells in your blood. The hematocrit test, also known as a packed-cell volume PCV test, is a simple blood test. More Information Iron deficiency anemia. Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Show references Sandoval C.
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