Introduction

The erythrocyte sedimentation rate (sedimentation rate, sed rate, and ESR for short) is a common hematology test that may indicate and monitor an increase in inflammatory activity within the body caused by one or more conditions such as autoimmune disease, infections or tumors.  The ESR is not specific for any one disease but is used in combination with other tests to determine the presence of increased inflammatory activity.  The ESR has long been used as a "sickness indicator" due to its reproducibility and low cost. Over many decades, several methods have evolved to perform the test.  However, the reference method for measuring the ESR proposed by the International Committee for Standardization in Haematology (ICSH) is based on the findings described by Westergren a century ago.[1]  Newer automated systems using closed blood collection tubes and automatic readers have been introduced into laboratories to decrease the biohazardous risk to operators and to decrease the time that it takes to perform the ESR.[2]

The Westergren method measures the distance (in millimeters) at which red blood cells in anticoagulated whole blood fall to the bottom of a standardized, upright, elongated tube over one hour due to the influence of gravity. The tube used for the test is called the Westergren tube. Today, these tubes are made of either glass or plastic, with an internal diameter of 2.5 mm and lengths of 190 to 300 mm long.[3]

Perhaps the first to notice a change in the sedimentation of blood due to illness was a British surgeon John Hunter (1728–93) in his posthumous publication A Treatise on the Blood, Inflammation, and Gun-Shot Wounds.[4] A Polish physician, Edmund Faustyn Biernacki (1866–1911), later refined the clinical use of the ESR near the end of the 19 century.[5] Biernacki detailed his findings in 2 articles in 1897 (the Gazeta Lekarska in Poland and the Deutsche Medizinische Wochenschrift in Germany), and he developed his test for measurements. These findings were not widely propagated in the English speaking medical communities. Because of his work, the ESR is occasionally referred to as the Biernacki Reaction world-wide.

The applied use of ESR in clinical diagnostics by Biernacki was furthered refined by Dr. Robert Fahraeus in 1918 and by Dr. Alf Vilhelm Albertsson Westergren in 1921.[6] Dr. Westergren defined the standard measurement of the ESR that is still in use today.[7] Together, Robert Fahraeus and Alf Vilhelm Albertsson Westergren are often remembered for the test, historically called the Fahraeus-Westergren test (FW test or Westergren test), which uses a standardized tube and sodium citrate anticoagulated blood.[1] 

The Westergren method for measuring the ESR proposed by the International Committee for Standardization in Haematology (ICSH) has allowed reproducibility for almost a century. Over time, the use of this same method has established comparable reference values within the same laboratory and even between different facilities across the globe. The Westergren method was adopted as the gold standard for ESR measurement in 1973 by the ICSH.[3]  Even after the advent of automated machines used for the analysis of the ESR, the Westergren method was still confirmed as the gold standard in 2011 by both the ICSH and by the Clinical and Laboratory Standards Institute (CLSI).

Pathophysiology

The ESR test measures the rate at which the red blood cells (RBCs), or erythrocytes, in a sample of whole blood, fall to the bottom of the Westergren tube. This process of "falling" is called sedimentation.

RBCs typically fall at a faster rate in people with inflammatory conditions such as infections, cancer, or autoimmune conditions. These conditions lead to an increase in the number of proteins in the blood. This increase causes red blood cells to stick together (clump) and settle at a faster rate. A group of RBCs that are clumped together will form a stack (similar to a stack of coins) called a rouleau (pleural is rouleaux).[8] Rouleaux formation is possible because of the particular discoid shape of RBCs. The flat surfaces of the RBCs allow them to make contact with other RBCs and stick together.

Normally, RBCs have negative charges on the outside of the cells, which cause them to repel each other. Many plasma proteins have positive charges and can effectively neutralize the negative surface charges of the RBCs, which allows for the formation of the rouleaux. Therefore, an increase in plasma proteins (present in inflammatory conditions) will propagate an increase in rouleaux formations, which settle more readily than single red blood cells[9] The settling of the rouleaux aggregates in the Westergren tube occurs at a constant rate. The formation of rouleaux allows the RBCs to settle at a faster rate, thus increasing the ESR.[10] Therefore, the ESR is not the measure of a single marker but a physical process. 

Rouleaux formation (and thus the ESR) is affected by the amounts of immunoglobulins and acute phase proteins (prothrombin, plasminogen, fibrinogen, C-reactive protein, alpha-1 antitrypsin, haptoglobin, complement proteins) that are present in several inflammatory conditions. "Acute-phase proteins" (APP) is the name given to a class of approximately 30 distinct, chemically unrelated plasma proteins that are innately regulated in response to infection and inflammation. APP's are produced by the liver and are functionally controlled by the body in response to several forms of tissue damage or insult. These proteins act as inhibitors or mediators of the inflammatory response. 

The detection of the first acute phase protein in the 1930s, the C-reactive protein (CRP), occurred during the analysis of the plasma of patients diagnosed with acute pneumococcal pneumonia.[11] The CRP and many other acute-phase proteins may increase during ongoing tissue damage, either acutely or chronically. "Acute phase" is still used to label these proteins that change in concentration during certain disease processes, regardless of chronicity. The fluctuating nature of the acute phase proteins in inflammation leads to the increased "stickiness" of RBC's, the formation of RBC "stacks" (rouleaux formation), and an increase in ESR.

Although many inflammatory illnesses will increase the ESR, other conditions exist that can lower the ESR. These "lowering factors" can exist either as isolated disease processes or in conjunction with other pathologic conditions that raise the ESR, thus giving a "lower than expected" ESR results in light of a serious underlying inflammatory process. Polycythemia (an increased number of red blood cells) will increase blood viscosity and can cause a reduced ESR (reduces the rate at which RBC rouleaux will settle to the bottom of the Westergren tube). Some hemoglobinopathies such as sickle cell disease can lower ESR due to the abnormal shape of red blood cells that impairs rouleaux formation. Spherocytosis (the presence of sphere-shaped rather than disc-shaped RBCs) also inhibits rouleaux formation and can decrease the ESR.

Specimen Requirements and Procedure

The Westergren method involves a simple blood draw that should take only a minute or two to obtain. A phlebotomist or other health care professional will obtain the blood sample. The skin directly over a vein is cleaned. Then, a needle is inserted into the vein to collect blood. After collecting, the needle is removed, and the puncture site is covered with a dressing to stop any bleeding.

Blood is typically collected in a black top ESR vacuum tube that contains a 3.2% sodium citrate anticoagulant. Whole blood collected in a lavender EDTA tube is also acceptable. The sample must be in its own tube (black or lavender) and cannot be combined with other tests due to the volume required. 

The blood sample will be sent to a laboratory. A lab technician will then transfer the anticoagulated whole blood to a vertical test tube (Westergren tube), which is inserted into the vacuum tube. When this sample is allowed to stand in the vertical tube for 1 hour, the red blood cells will slowly fall (settle) to the bottom due to the influence of gravity. This will leave a clear, straw-colored fluid at the top of the tube. This clear fluid is plasma, the portion of blood that remains after the red blood cells and other cellular components have settled to the bottom of the tube.

The test result will depend on the amount of plasma at the top of the tube, which will be measured after 1 hour. The result will be reported in millimeters per hour (mm/hr).

Diagnostic Tests

ESR can be measured by a variety of methods, including the Westergren, Wintrobe, and micro-ESR, along with the use of automated machines. Historically, the Westergren was the most commonly used method of performing the ESR. Technical factors, such as the amount of blood drawn into the tube, vibrations, temperature, time from specimen collection, the addition of proper anticoagulants, and tube orientation, can affect the results. RBC size, shape, and concentration can alter the ESR results. Plasma characteristics also have an impact on the value of the ESR.[12]

The Westergren method has classically been used to measure the ESR based on the distance that RBC’s settle to the bottom of an elongated tube with a 2.5 cm internal bore. It is graduated downward in millimeters, from 0 to 200, allowing the clear plasma to remain at the top of the tube after the RBC’s have settled toward the bottom due to gravitational force after 1 hour of observation.

Many additional methods have been proposed, including the Linzenmeier method, the Graphic or Cutler method, the Wintrobe-Landsberg method, and the Landau method. Only the Westergren and Wintrobe methods are common today. The Wintrobe method uses tubes of only 100 mm long with a smaller bore (thinner tube) than standard Westergren tubes. It is considered less sensitive than the Westergren.[13]

Although the Westergren method is commonly used for determining the ESR, it is time-consuming, and there is room for error. In an attempt to find faster and more reliable means of obtaining the ESR, newer methods have evolved. Some methods utilize a centrifuge and automated machines and can produce results in as quickly as 5 minutes.[14][15]

The micro ESR is a method of obtaining the ESR using capillary tubes and quicker testing times. This method uses 4 drops of capillary blood drawn from a finger poke that is then mixed in a 4:1 ratio on a slide with a 3.8 percent sodium citrate solution. The sample is then drawn into a 7.5-centimeter heparin-free microhematocrit capillary tube.[9] The results are measured at just 20 minutes and then adjusted to predict conventional ESR values from the micro ESR value.

Other automated methods for determining the ESR have become available. One study indicated that fewer labs are using the unmodified Westergren technique, and automated results using machines could differ from conventional results by 142%.[16]

Several new automated and semi-automated techniques have become available for determining the ESR that are safer and faster with a higher level of accuracy. The International Council for Standardization in Haematology (ICSH) has reviewed the accuracy and consistency of over a dozen methods. Recommendations have been made for the manufacturers for the validation of new ESR methods.[16] Recent studies indicate that automated measurements of the ESR have high comparability with the Westergren method.[17] Many automated machines do not measure sedimentation, but rather calculate a mathematically derived rate based on aggregate measurements in the early stages of RBC clumping (rouleaux formation). It will be up to the manufacturers and health care facilities to make sure that the new procedures are validated and verified.

Interfering Factors

Technical factors, such as seasonal variations in room temperature, time from specimen collection, tube orientation/ inclination, and vibration, can affect the results.[12][18] A higher room temperature decreases blood viscosity and may increase the ESR.[19] Direct sunlight can increase the ESR. A tilted ESR tube and vibrations may also cause an increase in the ESR value. An angle of 3 degrees from vertical can increase the ESR by 30 percent. Improper filling of the ESR tube may cause bubble formation and an increase in the ESR value. A blood sample that is allowed to sit too long before starting the test will cause RBC sphering and a decrease in the ESR value. The test should be run within two hours of collection. A clotted blood sample will inhibit rouleaux formation and decrease the ESR. The use of ESR tubes with inconsistent internal boreholes can be sensitive to clumps of RBCs and may lead to variations in the ESR results. Icteric blood samples (drawn from patients with liver disease) will produce a dark yellow plasma that may be difficult to differentiate from the sedimented RBCs upon direct inspection. Likewise, hemolysis (damaged erythrocytes) will cause the hemoglobin to leak into the plasma and subsequently turn the plasma red, making it difficult to differentiate from the sedimented RBCs.

Results, Reporting, Critical Findings

As with other tests, the actual reference range used for the ESR should be established by the laboratory performing the test.

Normal values for the erythrocyte sedimentation rate (ESR), as obtained using the Westergren method, are as follows:[20] [21]

• Male <50 years old ≤15 mm/hr
• Female <50 years old ≤ 20 mm/hr
• Male >50 years old ≤20 mm/hr
• Female >50 years old ≤30 mm/hr
• Child ≤10 mm/hr[22]

The ESR is typically higher in females than in males and increased gradually with age.[23]

Clinical Significance

Several factors may influence the ESR. Females tend to have slightly increased erythrocyte sedimentation rates compared to males. Pregnancy and aging may also increase the ESR. Anemia, RBC abnormalities, technical factors such as tilted ESR tubes, increased temperature of the specimen, and dilution errors may increase the ESR.

The ESR is neither sensitive nor specific as a general screening test. Because an elevated ESR may occur in multiple clinical settings, it is meaningless as a stand-alone laboratory value. Furthermore, some patients who have malignant lesions, serious infections, or significant inflammatory disorders may have normal ESR values. An ESR level that is elevated should heighten the practitioner's index of suspicion of the potential for underlying illness. This may include:

• Anemia
• Arteritis
• Infections (including bone and joint)
• Kidney disease
• Low serum albumen
• Lupus
• Lymphoma
• Multiple myeloma
• Polymyalgia rheumatica
• Red blood cell abnormalities
• Rheumatoid arthritis
• Systemic vasculitis
• Thyroid disease
• Waldenstrom macroglobulinemia

Any process that elevates fibrinogen (e.g., pregnancy, infection, diabetes mellitus, end-stage renal failure, heart disease, malignancy) may also elevate the ESR. An extremely high ESR value (>100 mm/hr) may indicate the presence of infection, multiple myeloma, Waldenstrom macroglobulinemia, temporal arteritis, polymyalgia rheumatica, or hypersensitivity vasculitis. One study reported that the average ESR was over 90 mm per hour in patients who had temporal arteritis, with values over 30 mm per hour in 99% of the patients.[24] The extremely high elevation of the ESR (>100 mm per hour) is associated with a low false-positive rate for a significant underlying illness.[25][26] Infection is likely the cause of an extreme elevation, followed by collagen vascular disease and metastatic tumors. In oncology, a high ESR tends to correlate with a poor prognosis for various types of cancers.[27][28][29][30]

An elevated ESR may be an important adjunct in detecting coronary artery disease. This is possibly linked to the inflammatory condition of coronary disease.[31][32][33]

• There may exist a relationship between the ESR in ischemic stroke and the amount of local brain injury, atherosclerosis, and short term outcomes.[34][35][36]
• Polymyalgia rheumatica and temporal (giant cell) arteritis are inflammatory conditions that usually occur in persons older than 50 years. The ESR is a useful test for diagnosing these illnesses.[37][20] However, lower ESR levels should not exclude these diagnoses.[38]
• In rheumatoid arthritis, systemic lupus, and osteoarthritis, ESR levels are frequently used to help make the diagnosis, yet the levels may be poorly correlated with the clinical aspects of disease intensity.[39] Some patients with active rheumatoid arthritis and synovial joint inflammation on biopsy will have a normal ESR.[40]
• Periprosthetic joint infection (PJI) is an adverse complication of total hip and knee arthroplasty. ESR has low sensitivity in a suspected PJI, ranging from 42% to 94%.[41]
• An isolated ESR is of variable sensitivity and not optimal to rule out septic arthritis. However, in combination with an inability to weight bear normally and increased temperature, the ESR may be a useful test, especially when using a low ESR threshold (>15 mm/hr).[42]
• An elevated ESR may be useful in the diagnosis and follow up in patients with osteomyelitis. Optimal ESR cutoff levels for the diagnosis are variable.[43][44] In cases of proven osteomyelitis, the ESR may be used to monitor response to therapy or relapse.[45]
• In cancers, an elevated erythrocyte sedimentation rate is associated with metastasis and worse prognosis in patients with cutaneous malignant melanoma.[46] High ESR has been found to correlate with overall poor prognosis for several cancer types, including breast, prostate, colorectal, Hodgkin disease, and chronic lymphocytic leukemia.[20]
• ESR may be used as an indicator of the presence of invasive bacterial infection in children.[47] The sensitivity of the ESR to detect a bacterial bone or joint infection on admission has been reported at 94% using an ESR cutoff of 20 mm/hr.[48]

Aside from factors that increase ESR, the health care team should consider the factors that decrease the ESR. This is especially important because circumstances may coexist that decreased the ESR result, leading to missed diagnoses. Factors that lower the ESR include an increased number of red blood cells (polycythemia), which causes an increase in blood viscosity. Hemoglobinopathies such as sickle cell disease can produce a lower ESR due to an improper shape of red blood cells that impairs stacking.[49][50]

Regular alcohol use is negatively associated with ESR. Alcohol drinkers of low, moderate, and high quantities of alcohol will show a lower ESR compared to abstainers and occasional drinkers. Moderate and high regular physical exercise were associated with lower than expected erythrocyte sedimentation rates.[23]

The test must be performed using blood that was drawn within two hours of testing. In standing blood, erythrocytes tend to become spherical, which impedes rouleaux formation. Anisocytosis and poikilocytosis also interfere with the stacking of erythrocytes, thus decreasing the ESR.

Certain medications (valproic acid, statins, nonsteroidal anti-inflammatory drugs) may lower the ESR value.[51][52]

Quality control and Lab Safety

The complex nature of coexisting factors influencing the ESR value, along with the potential for variations in the technique, have made it difficult to establish a reproducible testing method or an easily implemented quality control program to standardize procedures. Automated machines may offer the advantage of speed, laboratory safety, and reproducibility of results. The use of automated methods for determining the ESR has become more routine.[53]

Enhancing Healthcare Team Outcomes

Individuals with elevated ESR values may not always have a medical condition that requires treatment. A result outside of the usual range is not necessarily a cause for concern. Slightly higher levels can occur due to laboratory errors, pregnancy, menstruation, or advancing age. 

The ESR result may establish the presence of an inflammatory condition within the body, but the test is not specific for any disease process. It must be combined with other modalities in an attempt to define an underlying ailment. The use of the ESR as a screening test in asymptomatic patients is limited due to the low sensitivity and specificity. 

If there exists a suspicion of disease, the ESR may have some value as a “sickness index.” If the level is extremely elevated (>100 mm/hr), an apparent cause is usually present (malignancy, infection, temporal arteritis). If the level is mildly to moderately elevated without obvious causes, additional testing may be added in an extensive search for the underlying disease process. There is no evidence to suggest that an elevated ESR that is not supported by an alarming history, physical, or other modalities should prompt an extensive workup or further invasive procedures.[27][20] Simply repeating the ESR testing in an asymptomatic patient after several months may be indicated if a patient’s condition is stable. A continuously elevated ESR may then prompt a more expansive and expensive search for hidden disease.

Collaboration amongst the interprofessional team to correctly understand and interpret the results of the erythrocyte sedimentation rate is paramount to guide further diagnostics, therapeutics, and consultations for the overall benefit of the patient.