Introduction

The erythrocyte sedimentation rate (sedimentation rate, sed rate, or ESR for short) is a commonly performed 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 single 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 decrease the time 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.[3]

Perhaps the first to notice a change in blood sedimentation 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 19th century.[5] Biernacki detailed his findings in two articles in 1897 (the Gazeta Lekarska in Poland and the Deutsche Medizinische Wochenschrift in Germany) and 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 called the Biernacki Reaction worldwide.

The applied use of ESR in clinical diagnostics by Biernacki was refined by Dr. Robert Fahraeus in 1918 and 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, this same method has established comparable reference values within the same laboratory and even between different facilities across the globe. The ICSH adopted the Westergren method as the gold standard for ESR measurement in 1973.[3] Even after the advent of automated machines used to analyze the ESR, the Westergren method was still confirmed as the gold standard in 2011 by both the ICSH and the Clinical and Laboratory Standards Institute (CLSI).[8]

Pathophysiology

The ESR test measures the rate at which the red blood cells (RBCs), or erythrocytes, in a whole blood sample fall to the bottom of the Westergren tube. This process of "falling" is called sedimentation.[9] The red blood cells typically fall at a faster rate in people with inflammatory conditions such as infections, cancer, or autoimmune disorders. 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 faster. A group of RBCs clumped together will form a stack (similar to a stack of coins) called a rouleau (pleural, rouleaux).[10] 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.[11]

Typically, 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.[12] 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. Therefore, the ESR is not the measure of a single marker but a physical process. [13]

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.[14] "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.[15] APPs 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.[16] 

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.[17] The CRP and many other acute-phase proteins may increase during ongoing tissue damage, either acutely or chronically.[18] "Acute phase" is still used to label these proteins that change in concentration during specific disease processes, regardless of chronicity. The fluctuating nature of the acute phase proteins in inflammation leads to the increased "stickiness" of RBCs, the formation of RBC "stacks" (rouleaux formation), and an increase in ESR.[19]

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 result in light of a serious underlying inflammatory process.[20] 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).[21] 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.[22]

Specimen Requirements and Procedure

The Westergren method involves a simple blood draw that should take only a minute or two to obtain.[23] 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 collection, the needle is removed, and the puncture site is covered with a dressing to stop any bleeding.[24]

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.[25] 

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 one 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.[8]

The test result will depend on the amount of plasma at the top of the tube, measured after one hour. The result will be reported in millimeters per hour (mm/hr).[26]

Diagnostic Tests

ESR can be measured by various methods, including the Westergren, Wintrobe, micro-ESR, and automated machines.[27] 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.[28]

The Westergren method has classically been used to measure the ESR based on the distance RBCs 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 RBCs have settled toward the bottom due to gravitational force after one hour of observation.[8]

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 only 100 mm long with a smaller bore (thinner tube) than standard Westergren tubes. It is considered less sensitive than Westergren.[29]

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.[14] Some methods utilize centrifuge and automated machines and can produce results as quickly as five minutes.[30]

The micro-ESR is a method of obtaining the ESR using capillary tubes and quicker testing times. This method uses four drops of capillary blood drawn via fingerstick, 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.[12] 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 use the unmodified Westergren technique, and results using automated machines could differ from conventional results by 142%.[31]

Several new automated and semi-automated techniques have become available for determining the ESR; these methods are safer and faster with higher 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.[31] Recent studies indicate that automated measurements of the ESR have high comparability with the Westergren method.[32] 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 healthcare facilities to ensure the new procedures are validated and verified.[27]

Interfering Factors

Technical factors, such as seasonal variations in room temperature, time from specimen collection, tube orientation and inclination, and vibration, can affect the results.[28] A higher room temperature decreases blood viscosity and may increase the ESR.[33] Direct sunlight can increase the ESR. A tilted ESR tube and vibrations may also cause an increase in the ESR value. An angle of three degrees from vertical can increase the ESR by 30 percent. Improper filling of the ESR tube may cause bubble formation and increase the ESR value.[34]

A blood sample allowed to sit too long before starting the test will cause RBC sphering and decrease 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.[35] Using ESR tubes with inconsistent internal boreholes can be sensitive to RBC clumps 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 by direct inspection. Likewise, hemolysis (damaged erythrocytes) will cause hemoglobin to leak into the plasma and turn it red, making it difficult to differentiate from the sedimented RBCs.[36]

Results, Reporting, and Critical Findings

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

The ESR is typically higher in females than males and increases gradually with age.[26][20][37] [26]Normal values for the erythrocyte sedimentation rate (ESR), as obtained using the Westergren method, are as follows:

• 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 [38]

Clinical Significance

Several factors may influence the ESR. Females tend to have slightly increased ESRs compared to males.[26] Pregnancy and aging may also increase the ESR. Anemia, RBC abnormalities, technical factors such as tilted ESR tubes, increased specimen temperature, and dilution errors may increase the ESR.[39]

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 with malignant lesions, serious infections, or significant inflammatory disorders may have normal ESR values.[40] An elevated ESR level should heighten the practitioner's index of suspicion of the potential for underlying illness. These illnesses may include:

• Anemia
• Arteritis
• Infections (including bone and joint)
• Kidney disease
• Low serum albumin
• Systemic lupus erythematosus
• Lymphoma, including lymphoplasmacytic lymphoma
• Multiple myeloma
• Polymyalgia rheumatica
• Red blood cell abnormalities
• Rheumatoid arthritis
• Systemic vasculitis
• Thyroid disease

Any process that elevates fibrinogen levels (e.g., pregnancy, infection, diabetes mellitus, end-stage renal disease, heart disease, malignancy) may also elevate the ESR. An extremely high ESR value (>100 mm/hr) may indicate the presence of infection, multiple myeloma, lymphoplasmacytic lymphoma (Waldenström macroglobulinemia), giant cell (temporal) arteritis, polymyalgia rheumatica, or hypersensitivity vasculitis. One study reported that the average ESR was over 90 mm per hour in patients with temporal arteritis, with values over 30 mm per hour in 99% of the patients.[41] The extremely high elevation of the ESR (>100 mm per hour) is associated with a low false-positive rate for a significant underlying illness.[42] Infection is likely the cause of an extreme elevation, followed by collagen vascular disease and metastatic tumors.[43] In oncology, a high ESR tends to correlate with a poor prognosis for various types of cancers.[44][45]

• An elevated ESR may be an important adjunct in detecting coronary artery disease.[46][47] This is possibly linked to the inflammatory condition of coronary disease.[48]
• There may exist a relationship between the ESR in ischemic stroke and the amount of local brain injury, atherosclerosis, and short-term outcomes.[49][50]
• Polymyalgia rheumatica and giant cell (temporal) arteritis are inflammatory conditions that usually occur in persons older than 50 years.[51][20][51] The ESR is a useful test for diagnosing these illnesses. However, lower ESR levels should not exclude these diagnoses.[52]
• In rheumatoid arthritis, systemic lupus erythematosus, and osteoarthritis, ESR levels are frequently used to help make the diagnosis; the levels may be poorly correlated with the clinical aspects of disease intensity.[53] Some patients with active rheumatoid arthritis and synovial joint inflammation on biopsy will have a normal ESR.[54]
• 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%.[55]
• An isolated ESR is of variable sensitivity and is not optimal to rule out septic arthritis. However, in combination with an inability to bear weight normally and increased temperature, the ESR may be a helpful test, especially when using a low ESR threshold (>15 mm/hr).[56]
• 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.[57][58] In cases of proven osteomyelitis, the ESR may be used to monitor response to therapy or relapse.[59]
• An elevated ESR is associated with metastasis and a worse prognosis in patients with cutaneous malignant melanoma.[60] High ESR has been found to correlate with overall poor prognosis for several cancer types, including breast, prostate, colorectal, Hodgkin lymphoma, and chronic lymphocytic leukemia.[20]
• ESR may be used as an indicator of the presence of invasive bacterial infection in children.[61] 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.[62]

Aside from factors that increase ESR, the healthcare team should consider the factors that decrease ESR. This is especially important because circumstances that decrease the ESR may coexist with diagnoses that increase 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.[63] Hemoglobinopathies such as sickle cell disease can produce a lower ESR due to an improper shape of red blood cells that impairs stacking.[64]

Regular alcohol use is negatively associated with ESR. Alcohol drinkers of low, moderate, and high quantities of alcohol will show a lower ESR than abstainers and occasional drinkers. Regular physical exercise at moderate and high levels was associated with lower ESR rates than typically expected.[26]

The test must be performed using blood drawn within two hours of testing. In standing blood, erythrocytes tend to become spherical, which impedes rouleaux formation. Anisocytosis and poikilocytosis also interfere with erythrocyte stacking, thus decreasing the ESR.[14]

Certain medications (valproic acid, statins, nonsteroidal anti-inflammatory drugs) may lower the ESR value.[65][66]

Quality Control and Lab Safety

For non-waived tests, laboratory regulations require, at the minimum, analysis of at least two levels of control materials once every 24 hours. Laboratories can assay QC samples more frequently to ensure accurate results. Quality control samples should be assayed after calibration or maintenance of an analyzer to verify the correct method performance. To minimize QC when performing tests for which manufacturers’ recommendations are less than those required by the regulatory agency (such as once per month),[67] the labs can develop an individualized quality control plan (IQCP) that involves performing a risk assessment of potential sources of error in all phases of testing and putting in place a QC plan to reduce the likelihood of errors.[68] Westgard multi-rules are used to evaluate the quality control runs. In case of any rule violation, proper corrective and preventive action should be taken before patient testing.[69]

The laboratory must participate in the external quality control or proficiency testing (PT) program because it is a regulatory requirement published by the Centers for Medicare and Medicaid Services (CMS) in the Clinical Laboratory Improvement Amendments (CLIA) regulations.[70] It is helpful to ensure the accuracy and reliability of the laboratory with regard to other laboratories performing the same or comparable assays. Required participation and scored results are monitored by CMS and voluntary accreditation organizations. The PT plan should be included as an aspect of the quality assessment (QA) plan and the overall quality program of the laboratory.[71]

Consider all specimens, control materials, and calibrator materials as potentially infectious. Exercise the usual precautions required for handling all laboratory reagents. Disposal of all waste material should be in accordance with local guidelines. Wear gloves, a lab coat, and safety glasses when handling human blood specimens. Place all plastic tips, sample cups, and gloves that come into contact with blood in a biohazard waste container.[72] Discard all disposable glassware into sharps waste containers. Protect all work surfaces with disposable absorbent bench top paper, discarded into biohazard waste containers weekly or whenever blood contamination occurs. Wipe all work surfaces weekly.[73]

Enhancing Healthcare Team Outcomes

Individuals with elevated ESR values may not always have a medical condition that requires treatment. A result outside 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 to any disease process. It must be combined with other modalities 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 mild 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 not supported by an alarming history, physical, or other modalities should prompt an extensive workup or further invasive procedures.[43][20] 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 prompt a more expansive and expensive search for hidden diseases.

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