ERYTHROCYTE SEDIMENTATION RATE
PRINCINPLE: When anti-coagulated blood is allowed to stand undisturbed, the red blood cells will normally settle out to the bottom of the tube. This principle is the basis for the erythrocyte sedimentation rate(ESR). By definition, the ESR is the distance in millimeters that the red cells fall (in millimeters) per unit of time, which is usually 1 hour. Various factors will affect the ESR, such as the size and shape of the red cells, plasma fibrinogen, and globulin levels, as well as mechanical and technical factors. The ESR is directly proportional to the red cell mass and inversely proportional to the plasma viscosity. In normal whole blood red blood cells do not form rouleaux; the red cell mass is small and therefore the ESR is decreased (cells settle out slowly). In abnormal conditions when red cells can form rouleaux, the red cells mass is greater, thus increasing the ESR (cells settle out faster). Historically, there have been two methods for the erythrocyte sedimentation rate - the Wintrobe method and the Westergren method. Several newer methods, including an automated method, and modifications have been developed in recent years but have not been well-accepted. One newer modification of the ESR is capable of using smaller sample sizes, however, it has not been accepted as a standard procedure yet.
DISCUSSION: The ESR is a non-specific test procedure, but is useful as a screening test. It is of benefit in differentiating among certain disease processes that have similar symptomatology and in monitoring the course of an existing condition. It's primary use is in detecting inflammatory conditions. Inflammatory processes cause an increase in a number of proteins found in the blood. The increase in these proteins, such as fibrinogen, result in increased plasma viscosity and a resulting increased or accelerated erythrocyte sedimentation rate.
The ESR is affected by a number of mechanical and technical factors. These factors are :
1. It is absolutely essential that the ESR be on a level surface and that the table or area in which the tube is placed is free of vibration, direct sunlight (or other sources of heat), or drafts. A tilt of as little as 3o from vertical will affect the ESR.
2. The sample must be collected in an appropriate anticoagulant and in the proper proportion with the anticoagulant. EDTA is the anticoagulant of choice, but sodium citrate (blue-top tube) is also acceptable. Other anticoagulants can cause RBC shrinkage and as a result a falsely elevated ESR. It is important that the blood and anticoagulant be in the proper proportion since excessive anticoagulant can also cause shrinkage of the red cells.
3. The blood should be mixed thoroughly.
4. The ESR should be set up within 1 hour of collection of the sample. However, some authors agree that the sample can be held for up to 6 hours if the sample is refrigerated.
5. When the ESR tube is filled it must not contain any bubbles.
6. At the end of 60 minutes, the fall of the red cells is read as the level of the top of the red cell column in millimeters. If using a tube, such as the Win-trobe tube that has two scales, use the scale that starts at0 at the top. The ESR is read as the rate of fall of the red cells in millimeters per hour (mm/hr).
7. If the line of demarcation between the red cells and the plasma is hazy, take the level where the full density of red cells is first apparent.
8. Because the red cell shape affects the rate of fall of the cells, it should be apparent that sickle cells and spherocytes will result in a potential falsely decreased ESR. Other conditions that result in poikilocytosis (variation in the shape ofthe red cells) will produce similar results.
9. There is considerable dispute about the effect of severe anemia on the ESR. Some laboratories correct the ESR in cases of severe anemia.
10. Note that the normal ranges vary slightly with age, sex, and method.
11. Some Westergren tubes (almost all of the newer types) are self-zeroing. They have a cotton plug in the "zero" end. If the blood is pulled up to and into the cotton plug, you do not have to take any further action to zero the tube, since the blood caught in the cotton plug will not participate in the fall of the cells. The cotton plug will also prevent leakage of blood from the open end of the tube.
12. COMPARISON OF THE SEDIMENTATION RATE METHODS:The Westergren method is the most sensitive of the sedimentation rate methods because of the longer tube, but it re-quires more blood. The Wintrobe method requires a smaller amount of blood and involves no dilution. In addition, once the ESR has been read, the Wintrobe tube can be centrifuged to obtain a macro-hematocrit, and blood films can be made from the buffy coat. However, because of the shorter column of blood, the Wintrobe methods is not as sensitive as the Westergren.
PRINCINPLE: When anti-coagulated blood is allowed to stand undisturbed, the red blood cells will normally settle out to the bottom of the tube. This principle is the basis for the erythrocyte sedimentation rate(ESR). By definition, the ESR is the distance in millimeters that the red cells fall (in millimeters) per unit of time, which is usually 1 hour. Various factors will affect the ESR, such as the size and shape of the red cells, plasma fibrinogen, and globulin levels, as well as mechanical and technical factors. The ESR is directly proportional to the red cell mass and inversely proportional to the plasma viscosity. In normal whole blood red blood cells do not form rouleaux; the red cell mass is small and therefore the ESR is decreased (cells settle out slowly). In abnormal conditions when red cells can form rouleaux, the red cells mass is greater, thus increasing the ESR (cells settle out faster). Historically, there have been two methods for the erythrocyte sedimentation rate - the Wintrobe method and the Westergren method. Several newer methods, including an automated method, and modifications have been developed in recent years but have not been well-accepted. One newer modification of the ESR is capable of using smaller sample sizes, however, it has not been accepted as a standard procedure yet.
DISCUSSION: The ESR is a non-specific test procedure, but is useful as a screening test. It is of benefit in differentiating among certain disease processes that have similar symptomatology and in monitoring the course of an existing condition. It's primary use is in detecting inflammatory conditions. Inflammatory processes cause an increase in a number of proteins found in the blood. The increase in these proteins, such as fibrinogen, result in increased plasma viscosity and a resulting increased or accelerated erythrocyte sedimentation rate.
The ESR is affected by a number of mechanical and technical factors. These factors are :
1. It is absolutely essential that the ESR be on a level surface and that the table or area in which the tube is placed is free of vibration, direct sunlight (or other sources of heat), or drafts. A tilt of as little as 3o from vertical will affect the ESR.
2. The sample must be collected in an appropriate anticoagulant and in the proper proportion with the anticoagulant. EDTA is the anticoagulant of choice, but sodium citrate (blue-top tube) is also acceptable. Other anticoagulants can cause RBC shrinkage and as a result a falsely elevated ESR. It is important that the blood and anticoagulant be in the proper proportion since excessive anticoagulant can also cause shrinkage of the red cells.
3. The blood should be mixed thoroughly.
4. The ESR should be set up within 1 hour of collection of the sample. However, some authors agree that the sample can be held for up to 6 hours if the sample is refrigerated.
5. When the ESR tube is filled it must not contain any bubbles.
6. At the end of 60 minutes, the fall of the red cells is read as the level of the top of the red cell column in millimeters. If using a tube, such as the Win-trobe tube that has two scales, use the scale that starts at0 at the top. The ESR is read as the rate of fall of the red cells in millimeters per hour (mm/hr).
7. If the line of demarcation between the red cells and the plasma is hazy, take the level where the full density of red cells is first apparent.
8. Because the red cell shape affects the rate of fall of the cells, it should be apparent that sickle cells and spherocytes will result in a potential falsely decreased ESR. Other conditions that result in poikilocytosis (variation in the shape ofthe red cells) will produce similar results.
9. There is considerable dispute about the effect of severe anemia on the ESR. Some laboratories correct the ESR in cases of severe anemia.
10. Note that the normal ranges vary slightly with age, sex, and method.
11. Some Westergren tubes (almost all of the newer types) are self-zeroing. They have a cotton plug in the "zero" end. If the blood is pulled up to and into the cotton plug, you do not have to take any further action to zero the tube, since the blood caught in the cotton plug will not participate in the fall of the cells. The cotton plug will also prevent leakage of blood from the open end of the tube.
12. COMPARISON OF THE SEDIMENTATION RATE METHODS:The Westergren method is the most sensitive of the sedimentation rate methods because of the longer tube, but it re-quires more blood. The Wintrobe method requires a smaller amount of blood and involves no dilution. In addition, once the ESR has been read, the Wintrobe tube can be centrifuged to obtain a macro-hematocrit, and blood films can be made from the buffy coat. However, because of the shorter column of blood, the Wintrobe methods is not as sensitive as the Westergren.
INTERPRETATION AND COMMENTS
NORMAL RANGES FOR WINTROBE: MALES: 0-7 mm/hr FEMALES: 0-15mm/hr
WESTERGREN: MEN
<50 years old, 0-10 mm/hr MEN >50
years old, 0-20mm/hr WOMEN:
<50 years old, 0-20 mm/hr WOMEN: >50 years old,
0-30 mm/hr
NORMAL RANGES FOR WINTROBE: MALES: 0-7 mm/hr FEMALES: 0-15mm/hr
WESTERGREN: MEN <50 years old, 0-10 mm/hr MEN >50 years old, 0-20mm/hr WOMEN:
<50 years old, 0-20 mm/hr WOMEN: >50 years old,
0-30 mm/hr
WESTERGREN: MEN <50 years old, 0-10 mm/hr MEN >50 years old, 0-20mm/hr
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