Microhematocrit

Principle

The hematocrit or packed cell volume measures the concentration of red blood cells (RBCs) in a given volume of whole blood in a capillary tube. This volume is measured after appropriate centrifugation time and is expressed as a percentage of the total blood sample volume. A whole blood sample in an anticoagulated tube is

Qualitative D-Dimer Test

Principle

Reagents and Equipment

Specimen Collection and Storage

Quality Control

Procedure

Interpretation

Results

Limitations

An Approach to Interpreting Automated Hematology Data

Principle Instruments

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Overview Principles

Data Interpretation: One Role for the Medical Technologist

Flow Cytometry Case Studies centrifuged at 10,000 to 13,000 rpm for 5 minutes. Ery-throcytes are packed at the bottom of the capillary tube and the hematocrit is expressed as a measurement of this level compared to the plasma level. The interface between plasma and red cells is marked by a buffy coat that is composed of leukocytes and platelets. The hematocrit percentage is read below the buffy coat layer. A microhematocrit value can assist in evaluating fluid status, in clarifying various degrees of anemia, and in monitoring acute hemorrhagic conditions. The hematocrit value is also useful in calculating indices, which in turn can help determine the morphological classification of anemias.

Reagents and Equipment

1. Microhematocrit centrifuge (Fig. 20.1)

2. Microhematocrit reader disk

3. Capillary tubes (Fig. 20.2)

a. Plain-blue tip (for EDTA [ethylenedi-aminetetraacetic acid] tubes)

b. Heparinized-red tip (for Microtainer specimens)

Note: both types of tubes contain self-sealing clay

4. Mechanical rocker

Figure 20.1 Standard microhematocrit centrifuge. Maximum packing time is dependent on a calibrated centrifuge.

Specimen Collection and Storage

1. Fresh whole blood collected in EDTA in which the patient tube is at least half full.

2. Capillary blood collected in an EDTA Microtainer.

Quality Control

Hematocrits are run in duplicate and must agree within ±1%.

Procedure

1. Mix EDTA tube by placing on a mechanical rocker for 3 minutes.

2. After adequate mixing, fill the self-sealing capillary tubes two thirds to three fourths full. Prepare the tubes in duplicate.

3. Wipe the outside of the capillary tubes with lint-free wipe or gauze.

4. Invert the tube so that the blood runs to sealed end.

5. Place the tubes directly across from each other in the microhematocrit centrifuge, with the sealed ends away from the center of centrifuge.

6. Record the identification and the position number of each patient specimen.

7. Place the head cover and hand-tighten only. Close the outer lid.

8. Centrifuge for 5 minutes, for maximum packing.

9. Remove the tubes from the centrifuge and place in the microhematocrit reader. Read the hematocrit according to the manufacturer's instructions. The results are recorded in percent. The tubes should match within ±1%.

Interpretation

The spun capillary tube should have three visible sections: RBCs, buffy coat (contains leukocytes and platelets), and plasma. Read the hematocrit results by placing the centrifuged capillary tube in the groove of the plastic indicator reader. The bottom of the red cell column should meet with the black line on the plastic indicator (Fig. 20.3).

1. Rotate the bottom plate so the 100% line is directly beneath the red line on the plastic indicator and hold the bottom plate in this position. With use of the finger hole, rotate the top plate so that the spiral line intersects the capillary tube at the plasma air space.

2. Rotate both discs together until the spiral line intersects the capillary tube at the white cell-red cell line.

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