Modified Westergren Sedimentation Rate

Principle

The erythrocyte sedimentation rate (ESR) is a nonspecific screening test indicative of inflammation. It is used as an initial screening tool and also as a follow-up test to monitor therapy and progression or remission of disease. This test measures the distance that RBCs will fall in a vertical tube over a given time period. The ESR is directly proportional to red cell mass and inversely proportional to its surface area. The ESR is reported in millimeters. Any condition that will increase rouleaux formation will usually increase the settling of red cells. Factors affecting the ESR are as follows:

• Red cell shape and size: Specimens containing sickle cells, acanthocytes, or spherocytes will settle slowly and give a decreased ESR

• Plasma fibrinogen and globulin levels: Increased fibrinogen or globulin levels will cause increased settling and give an increased ESR • Mechanical and technical conditions: Surfaces that are not level will influence red cell settling. Specimens that are not properly anticoagulated will also affect red cell settling. EDTA is the recommended anticoagulant.

Reagents and Equipment

1. Sediplast Autozero Westergren ESR system (Fig. 20.4)

a. Fixed bore pipettes b. Sedivials filled with 0.2 mL of 3.8% sodium citrate c. Vial holder (rack)

2. Disposable plastic pipettes

3. Rotator/mixer

4. Timer

Specimen Collection and Storage

Specimens are collected in EDTA. Tubes must be at least half full, well mixed, and free of clots and/or fibrin. ESR can be set up on specimens at room temperature up to 4 hours old. Refrigerated specimens (2 to 8°C) can be set up until 24 hours old.

Figure 20.4 Sediplast ESR rack. The sample must be placed on a level surface with no vibration.

Quality Control

Commercially prepared controls stored at 2 to 8°C are valid until expiration date. Controls are prepared like patients' specimens. Controls are run once daily prior to setting up patient tests. Do not report out patient results unless controls are in reference range.

Procedure

1. Mix the EDTA tube on the rotator/mixer for a minimum of 5 minutes. If the sample has been refrigerated, allow 30 minutes for the sample to come to room temperature before proceeding.

2. Remove the top of the Sediplast vial, which contains 3.8% sodium citrate. Using a disposable pipette, add blood to the indicated line, return the top, and mix thoroughly.

3. Insert Westergren tube into Sediplast vial with a slight twist, allowing the blood to rise to the zero mark.

4. Place the vial in the rack on a level surface.

5. Set a timer for one hour and read at the end of the hour.

6. Record the ESR in millimeters per hour.

Normal Ranges

Men 0 to 15 mm/hr Women 0 to 20 mm/hr

Limitations

1. Tubes not filled properly will yield erroneous results.

2. Refrigerated specimens must come to room temperature for 30 minutes prior to testing.

3. The ESR rack must be on a level surface and free of vibration. Vibration can cause a falsely increased ESR.

4. Cold agglutinins can cause a falsely elevated ESR. An ESR can be performed at 37°C (incubator) for 60 minutes with no ill effects.

5. Cell size and shape affect ESR, usually resulting in a decreased ESR result.

6. Increased rouleaux formation, excessive globulin, or increased fibrinogen will increase the ESR.

7. Specimen must be free of clots and/or fibrin.

8. A tilted ESR tube gives erroneous results.

9. Hemolyzed samples are not acceptable. 10. Specimens older than 24 hours are not acceptable.

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