All over the world, healthcare professionals rely on accurate and precise laboratory test results to make the right diagnosis and treatment decisions. In the investigation of inflammation, ESR measurement is often the first line test of choice as it’s simple, inexpensive and- if based on the Westergren method- reliable, reproducible and sensitive. But as is the case with every test, there are physiological and clinical factors that may influence ESR results. In this article, we’ll tell you more about them.
Before you start reading….
When reading about factors that influence ESR results, please keep in mind that much, if not all of this information, is based on studies undertaken with the Westergren gold standard ESR method only. This is mainly due to the fact that the Westergren ESR method has been almost universally used to investigate the clinical utility of the test in a range of disease states, with much of this work published in peer reviewed journals. As a result, there’s a deep body of knowledge that describes the impact of disease, the limitations and sources of interference with the Westergren ESR. As the Westergren method for ESR measures a physical process under a defined set of conditions, this expansive body of knowledge cannot simply be “transferred” to estimations of ESR by methods that use centrifugation or optical rheology.
What’s normal in ESR?
Before discussing the factors that influence ESR results, first we should answer the question: what is normal? As you probably know, ESR is the rate at which red blood cells settle. When patients suffer from a condition that causes inflammation, their red blood cells form clumps which makes them settle faster than they would in the absence of an inflammatory response. However, “faster” is a relative term, and what’s normal changes based on sex and age category:
- Women under age 50: ESR under 20 mm/hr.
- Men under age 50: ESR under 15 mm/hr.
- Women over age 50: ESR under 30 mm/hr.
- Men over age 50: ESR under 20 mm/hr.
- Children: ESR between 0 and 10 mm/hr.
Physiological and clinical factors that increase ESR
The most obvious explanation for increased ESR is inflammation. During acute phase reactions, macromolecular plasma proteins, particularly fibrinogen, are produced that decrease the negative charges between red blood cells and thereby encourage the formation of cell clumps. And as cell clumps settle faster, this increases ESR. Inflammation indicates a physical problem, meaning additional tests and follow up are needed. However, there are other factors that increase ESR but don’t necessarily come with inflammation. For example, ESR values are higher for women than for men and increase progressively with age. Pregnancy also increases ESR, which means you’ll be dealing with ESR results above average. In anemia, the number of red blood cells is reduced, which increases so-called rouleaux formation so that the cells fall faster. This effect is strengthened by the reduced haematocrit, which affects the speed of the upward plasma current. Another factor that increases ESR revolves around high protein concentrations. And in macrocytosis, red blood cells have a shape with a small surface-to-volume ratio, which leads to a higher sedimentation rate.
Physiological and clinical factors that decrease ESR
Apart from factors that increase ESR, medical practitioners and laboratory scientists should also consider the factors that decrease ESR. This is especially important as decreased ESR results may lead to missed diagnoses, whereas increased ESR results either lead to the right follow up or false positives. Polycythaemia, caused by increased numbers of red blood cells or by a decrease in plasma volume, artificially lowers ESR. Red blood cell abnormalities also affect aggregation, rouleaux formation and therefore sedimentation rate. Another cause of a low ESR is a decrease in plasma proteins, especially of fibrinogen and paraproteins.
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