Accurate lab tests play an essential role in healthcare all around the world. Not only do physicians need them to find out what’s wrong with their patients; they help them decide on the appropriate follow up. As a wrong diagnosis can have serious (or fatal) consequences, doing the right tests in the right order is critically important. This is why, often, medical practitioners start off with an ESR: a non-specific marker that tests patients for several conditions. What makes ESR measurement so effective? And what do you need to make it a reliable test? We’ll tell you in this article.
Explaining ESR measurement
ESR stands for Erythrocyte Sedimentation Rate. Medical practitioners use the ESR test in combination with clinical history and -of course- physical examination to help in the differential diagnosis of their patients. The test checks the speed at which red blood cells settle in a test tube, and if the amount of settled red blood cells diverges from the norm. If this is indeed the case, there’s evidence of inflammation, meaning further investigations are needed to discover the underlying issue.
Applications of ESR measurement
There’s a long list of conditions for which ESR can be used to assist clinicians in making a correct diagnosis or managing the care of a patient. Autoimmune diseases such as rheumatoid arteritis (RA), temporal arteritis and polymyalgia rheumatica are well known examples, just as multiple myeloma. For the clinician that suspects the presence of inflammation, ESR is a simple and cost-effective way of confirming this. Moreover, for patients that have a known condition and are being managed, the ESR test can provide useful information into the overall effectiveness of their treatment.
The Westergren method
The discovery of the ESR dates back to 1794, but in the 1920s, pathologist Robert Fåhræus and Alf Westergren developed ESR measurement as we know it. To this day, the so-called Westergren method is recognised as the gold standard, among others by the Clinical and Laboratory Standards Institute (CLSI). In 2017, the International Council for Standardization in Hæmatology (ICSH) reconfirmed the Westergren method as the reference method for ESR measurement. The Westergren method owes its popularity to the fact that it’s a simple and inexpensive first line test, providing valuable information to GPs in the investigation of inflammation after only 60 (or even 30) minutes.
Critical factors of a reliable ESR test
The Westergren method may be the gold standard; many factors can meddle with its reliability. Therefore, always keep in mind the following requirements:
- Non-hemolyzed blood anti-coagulated with EDTA at collection
- Blood sample is thoroughly mixed and diluted 4:1 using a sodium citrate solution
- The tube is held in vertical position at a constant temperature (± 1°C) between 18°C and 25°C in an area free from vibrations, drafts and direct sunlight
- Results are interpreted after at least 30 minutes
Can we speed up ESR measurement?
In the original Westergren method, the ESR is read after 60 minutes. You can imagine this puts practical limitations on the workflow in clinical laboratories. A laboratory investigation however showed that 30-minute ESR readings correlate highly with the corresponding 60-minute ESR readings, which is why today, most laboratories perform 30-minute ESR readings and extrapolate them to the corresponding ESR reading at 60 minutes afterwards. There are Westergren alternatives that claim to measure ESR after only 20 seconds, but as it takes at least 10 minutes before sedimentation starts at a constant rate, these tests risk leading to a number of false negatives.
Want to know more about the use of ESR measurement, the Westergren method and why it’s still the gold standard? Download the white paper below!