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Submit Cancel. Thank you for submitting a comment on this article. Your comment will be reviewed and published at the journal's discretion. 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. The membrane of the erythrocytes is electrically insulating, mainly due to its content of lipids, so that it appears essentially non-conducting.
Due to this, there is an inverse relationship between the electrical conductance and the hematocrit in blood when the concentration of the charged particles is taken into account. 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: Electrolytes Temperature Proteins Most blood gas analyzers allow for these variables as follows: Concentration of electrolytes: This is determined by one or more ion measurements.
As sodium is the primary electrolyte in plasma, this is the most important ion to measure and use in the calculation of hematocrit. A change in the temperature has a significant impact on the conductivity because blood has a high temperature coefficient.
The measuring chamber in blood gas analyzers is thermostatted and the blood sample preheated prior to measurement; thus there is no contribution from changing temperature. The protein concentration in plasma is assumed constant in healthy people, so a constant compensation for this is incorporated in the calculation of hematocrit on blood gas analyzers.
Limitations: In patients with abnormal plasma osmolality, e. Some blood gas analyzers offer correction for this bias [10,11,12].
Calculation of hematocrit from hemoglobin 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 analytical quality of the c tHb measurement The precision of the equation that converts the two parameters 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.
Hematocrit and hemoglobin are often used interchangeably; however, different studies have shown that the two parameters are not comparable, but that they have their separate applications [15,17,18,19]. Comparing measuring technologies All measuring technologies for determining hematocrit have advantages and disadvantages.
Table as word document. Method Advantages Microhematocrit Small sample volume Relatively fast analysis Hemolysis detected when result is read No dilution needed Complete blood cell count Hct parameter together with other hematology parameters — only one blood sample is necessary Dilution of sample removes problems with hyperosmotic samples No preparation needed No manual dilution needed Conductivity Small sample volume Short turnaround time Hct parameter together with blood gas, pH, electrolytes, and metabolites — only one blood sample is necessary No preparation needed No dilution needed Suitable for POCT Calculation from c tHb Hct parameter together with other parameters — only one blood sample is necessary Some methods are suitable for POCT TABLE IIa.
Advantages of different methods of measuring hematocrit. Method Disadvantages Microhematocrit Time-consuming and careful preparation required sealing of capillaries, etc Uncertain manual reading of the ratio Leakage of sealing gives falsely low results more RBCs will be lost than plasma [5] Falsely high Hct readings caused by trapped plasma.
Arterial blood has approx. Disadvantages of different methods of measuring hematocrit. Discussion When hematocrit is used to assess anemia and the oxygen-carrying capacity, the advantages and disadvantages of each method must be carefully considered. Conclusion Both POCT and traditional laboratory methods of measuring or calculating hematocrit have limitations.
Biochemical Basis of Pediatric Disease. Second ed. Kokholm G. Simultaneous measurements of blood pH, p CO 2 , p O 2 and concentrations of hemoglobin and its derivatives — a multicenter study. Radiometer publication AS Procedure for determining packed cell volume by the hematocrit method.
Third edition. Fourth edition. Louis, Missouri: Mosby, Hematocrit HCT. In: Thomas L, ed. Clinical laboratory diagnostics, use and assessment of clinical laboratory results.
Known interfering substances. Code no. Analytical artifacts in hematocrit measurements by whole-blood chemistry analyzers. Clin Chem ; 41, 2: User-defined corrections.
Krarup T, Walcker KS. Guideline to measurement on the ABL using the user-specified fluid mode. Radiometer publication Bulletin No. Deriving a useful packed cell volume estimate from haemoglobin analysis. J Clin Pathol ; Clin Lab Haem ; Evaluation of automated methods of measuring hemoglobin and hematocrit in horses. AJVR ; 59, Hemoglobins and hematocrits: are they equally sensitive in detecting anemias?
Am J Clin Nutr ; 34, 1: Evaluation of the capillary microhematocrit as a screening test for anemia in pediatric office practice. Anemic or not? Performance characteristics. Laboratory Test Handbook. Hudson, Cleveland: Lexi-comp inc, The whole-blood sampling handbook. Acute care testing handbook Get the acute care testing handbook Your practical guide to critical parameters in acute care testing. Download now. Scientific webinars Check out the list of webinars Radiometer and acutecaretesting.
Go to webinars. Sign up for the Acute Care Testing newsletter Sign up. About this site. About Radiometer. Privacy Policy. This site uses cookies Read more. Close banner. Conversion equation. Small sample volume Relatively fast analysis Hemolysis detected when result is read No dilution needed.
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