A WSR blood test, short for Westergren sedimentation rate, measures how quickly your red blood cells settle to the bottom of a narrow tube over one hour. It’s one of the oldest and most common lab tests for detecting inflammation in the body. You might also see it called an ESR (erythrocyte sedimentation rate), sed rate, or simply “sedimentation rate.” Normal values generally fall between 0 and 15 mm/hr for men and 0 and 20 mm/hr for women.
How the Test Works
A technician draws a standard blood sample from your arm and places it in a tall, narrow tube called a Westergren tube. The tube stands upright for exactly one hour while gravity pulls red blood cells downward. At the end of that hour, the technician measures how far the cells have fallen, in millimeters. That distance is your WSR result.
When your body is fighting inflammation, your liver produces more of certain proteins that cause red blood cells to clump together. These clumps are heavier and sink faster, producing a higher number. So a WSR doesn’t identify a specific disease. It tells your doctor that something in your body is driving an inflammatory response, and roughly how intense that response is.
Normal Ranges by Age and Sex
WSR values naturally vary by sex and increase with age. The commonly used reference ranges are:
- Men under 70: 0 to 15 mm/hr (some newer data suggests up to 14 to 18 mm/hr as the upper limit)
- Men 70 and older: up to about 22 to 25 mm/hr
- Women over 18: 0 to 20 mm/hr (with some labs using up to 22 to 25 mm/hr)
The Westergren method remains the gold standard endorsed by the International Council of Standardization in Haematology, though many labs now use automated analyzers that correlate their results to this method. Your lab report will list the specific reference range it uses, so check the numbers printed alongside your result rather than relying on general guidelines alone.
Why Your Doctor Orders It
A WSR is rarely used on its own to diagnose anything. It’s a screening and monitoring tool, almost always paired with other blood tests or imaging. Your doctor might order one if you have unexplained symptoms like persistent fever, joint stiffness, headaches, weight loss, neck or shoulder pain, or loss of appetite.
The test is especially useful for two conditions. Polymyalgia rheumatica, which causes widespread muscle pain and stiffness (particularly in the shoulders and hips), typically produces a noticeably elevated WSR. Giant cell arteritis, an inflammation of the arteries in the scalp and neck, is one of the few conditions where a specific WSR threshold matters clinically. The American College of Rheumatology includes a WSR above 50 mm/hr as one of its classification criteria for this condition. A normal WSR makes giant cell arteritis unlikely, though it doesn’t completely rule it out.
Doctors also use the WSR to track how well treatment is working for chronic inflammatory conditions like rheumatoid arthritis, lupus, or inflammatory bowel disease. A falling number over weeks or months suggests the inflammation is coming under control.
What a High Result Means
A high WSR signals that inflammation is present somewhere in the body, but it doesn’t point to where or why. The list of possible causes is long:
- Autoimmune conditions: rheumatoid arthritis, lupus, vasculitis, ankylosing spondylitis, Sjögren’s disease
- Infections: urinary tract infections, pneumonia, bone infections, endocarditis
- Cancers: lymphoma, multiple myeloma, and some solid tumors like ovarian or lung cancer
- Other inflammatory conditions: Crohn’s disease, celiac disease, sarcoidosis, kidney disease
In a study of patients with elevated WSR who had no prior rheumatic diagnosis, infections accounted for about 25% of cases and cancers for roughly 9%. Among those who did receive a new rheumatic diagnosis, polymyalgia rheumatica and giant cell arteritis were the most common (38%), followed by rheumatoid arthritis (24%) and Sjögren’s disease (12%).
What a Low Result Means
An unusually low WSR is less commonly discussed but does occur. Conditions that change the shape or number of red blood cells can slow sedimentation. Polycythemia (an abnormally high red blood cell count) is the most common cause. Sickle cell disease and hereditary spherocytosis also produce low readings because irregularly shaped cells don’t stack and clump the way normal cells do. Severe heart failure and very low levels of clotting proteins can lower the result as well.
Factors That Affect Your Results
Several things besides disease can push your WSR up or down. Age is the biggest one: values drift higher as you get older, which is why reference ranges widen for people over 70. Women tend to have higher values than men at any age, and pregnancy raises the WSR significantly because of changes in blood protein levels.
Body weight matters too. Higher BMI and metabolic syndrome are independently associated with elevated WSR values. Smoking also tends to push the number up. On the other hand, regular physical activity and light alcohol consumption are linked to lower readings. Anemia raises the WSR because fewer red blood cells settle differently in the tube, so your doctor will usually interpret an elevated WSR alongside your complete blood count to rule out this effect.
No fasting or special preparation is needed before the test. It’s a simple blood draw, typically processed alongside whatever other tests your doctor has ordered.
How WSR Compares to CRP
C-reactive protein (CRP) is the other common blood marker for inflammation, and it works differently. CRP is a specific protein your liver releases during inflammation. It rises and falls much faster than the WSR, with concentrations doubling or halving in about six hours and peaking within two days. The WSR, by contrast, may take weeks to normalize after inflammation resolves because it depends on protein changes that linger in the blood.
This speed difference has practical consequences. CRP is better at catching inflammation early, when the WSR might still look normal. It’s also more reliable for tracking rapid changes, like whether an acute infection is responding to treatment. The WSR is more likely to produce a false positive (elevated without true inflammation) because so many non-inflammatory factors influence it.
There are two situations where the WSR can actually outperform CRP. Low-grade bone and joint infections, particularly around joint replacements caused by slow-growing bacteria, sometimes raise the WSR while CRP stays normal. And in lupus, the CRP can remain normal even during active disease flares, making the WSR a more reliable indicator of what’s happening.
Many doctors order both tests together. When CRP is elevated but the WSR is normal, infection or recent tissue damage (like a heart attack or blood clot) is more likely. When the WSR is high but CRP is normal, the cause is more often a condition without obvious acute inflammation, such as certain cancers.