What is Sed Rate (Erythrocyte Sedimentation Rate)? Purpose, Levels, Procedure & Results

The sed rate, or erythrocyte sedimentation rate (ESR), is a simple blood test that measures how quickly your red blood cells settle at the bottom of a test tube. This test helps your doctor detect inflammation in your body, though it doesn't pinpoint exactly where the inflammation is coming from.

Think of it like watching sand settle in water - when there's inflammation in your body, certain proteins make your red blood cells clump together and fall faster than normal. The sed rate has been a trusted tool in medicine for nearly a century, and while newer tests exist, it remains valuable for monitoring many health conditions.

What is sed rate?

Sed rate measures how far your red blood cells fall in a tall, thin tube over the course of one hour. Normal red blood cells fall slowly and steadily, but when inflammation is present, they tend to stick together and drop more quickly to the bottom.

The test gets its name from the process itself - "sedimentation" simply means settling or sinking. Your red blood cells (erythrocytes) naturally have a tendency to settle due to gravity, but inflammation changes how fast this happens.

During inflammation, your liver produces more proteins called fibrinogen and immunoglobulins. These proteins make your red blood cells cluster together into coin-like stacks, which are heavier and fall faster than individual cells.

Why is sed rate done?

Your doctor orders a sed rate test primarily to detect and monitor inflammation in your body. It's particularly useful when you have symptoms that suggest an inflammatory condition but the cause isn't immediately clear.

The test serves several important purposes in medical care. First, it helps screen for inflammatory diseases like rheumatoid arthritis, lupus, or inflammatory bowel disease. Second, it monitors how well treatment is working for existing inflammatory conditions.

Your doctor might also use sed rate to track the progress of infections, especially serious ones like endocarditis (heart infection) or osteomyelitis (bone infection). However, the test isn't specific enough to diagnose any particular condition on its own.

Sometimes sed rate is ordered as part of routine screening, especially in older adults, since the rate tends to increase naturally with age. It can also help distinguish between different types of arthritis or monitor cancer treatment response.

What is the procedure for sed rate?

The sed rate test requires only a simple blood draw, usually from a vein in your arm. The entire process takes just a few minutes and feels similar to any other blood test you've had.

Here's what happens during the test:

1. A healthcare worker cleans your arm with an antiseptic
2. They tie a tourniquet around your upper arm to make veins more visible
3. A small needle is inserted into a vein to draw blood
4. The blood is collected in a special tube
5. The needle is removed and a bandage is applied

After collection, your blood sample goes to the laboratory where it's placed in a tall, narrow tube called a Westergren tube. The lab technician measures exactly how far the red blood cells fall in one hour.

The most common method used today is the Westergren method, which uses a 200mm tube and dilutes your blood with sodium citrate to prevent clotting. Some labs use automated methods that can give results faster.

How to prepare for your sed rate test?

The good news is that sed rate testing requires no special preparation on your part. You can eat normally, take your usual medications, and go about your regular activities before the test.

Unlike some blood tests that require fasting, sed rate measures something that isn't affected by food or drink. You don't need to avoid coffee, skip breakfast, or change your routine in any way.

However, it's helpful to wear a shirt with sleeves that can be easily rolled up or pushed aside. This makes it easier for the healthcare worker to access your arm for the blood draw.

If you're taking any medications, continue taking them as prescribed unless your doctor specifically tells you otherwise. Some medications can affect sed rate results, but stopping them without medical guidance could be more harmful than any test interference.

How to read your sed rate results?

Sed rate results are reported in millimeters per hour (mm/hr), which tells you how far your red blood cells fell in the test tube during one hour. Normal ranges vary based on your age and sex, with women typically having slightly higher normal values than men.

For men under 50, normal sed rate is typically 0-15 mm/hr, while men over 50 have normal values of 0-20 mm/hr. Women under 50 usually have normal values of 0-20 mm/hr, and women over 50 may have normal values up to 30 mm/hr.

A high sed rate suggests inflammation somewhere in your body, but it doesn't tell you where or what's causing it. Values above 100 mm/hr often indicate serious conditions like severe infections, autoimmune diseases, or certain cancers.

Keep in mind that sed rate naturally increases with age, so what's considered high for a 30-year-old might be normal for a 70-year-old. Your doctor will interpret your results in the context of your age, symptoms, and other test results.

What causes high sed rate?

High sed rate can result from many different conditions, ranging from minor infections to serious autoimmune diseases. Understanding the potential causes can help you have more informed discussions with your healthcare provider.

Common causes of elevated sed rate include:

• Bacterial infections like pneumonia or urinary tract infections
• Viral infections, though these typically cause smaller increases
• Autoimmune conditions like rheumatoid arthritis or lupus
• Inflammatory bowel diseases such as Crohn's disease or ulcerative colitis
• Certain cancers, especially blood cancers like lymphoma
• Kidney disease or liver problems
• Thyroid disorders

Less common but serious causes include giant cell arteritis (inflammation of blood vessels), polymyalgia rheumatica (muscle pain and stiffness), and certain heart conditions. Some medications can also elevate sed rate.

Pregnancy naturally increases sed rate, especially in the second and third trimesters. This is completely normal and doesn't indicate any health problems with you or your baby.

What causes low sed rate?

Low sed rate is less common and usually less concerning than high values. Sometimes a low result is simply normal for you, especially if you're young and healthy.

Several conditions can cause unusually low sed rate values:

• Sickle cell disease, where abnormally shaped red blood cells don't settle normally
• Polycythemia (too many red blood cells), making the blood thicker
• Severe heart failure, which can affect blood flow
• Certain medications like aspirin or corticosteroids
• Extreme leukocytosis (very high white blood cell count)

Some rare conditions like hyperviscosity syndrome or certain protein abnormalities can also cause low sed rate. However, these conditions usually have other obvious symptoms.

In most cases, a low sed rate is actually a good sign, suggesting you don't have significant inflammation in your body. Your doctor will consider this result along with your symptoms and other tests.

What are the risk factors for abnormal sed rate?

Several factors can increase your likelihood of having an abnormal sed rate, though many of these are related to underlying health conditions rather than the test itself.

Age is the most significant factor affecting sed rate. As you get older, your normal sed rate gradually increases, which is why reference ranges are different for different age groups.

Being female also tends to result in slightly higher normal values, particularly during menstruation, pregnancy, and after menopause. Hormonal changes throughout a woman's life can influence sed rate results.

Other risk factors include:

• Having an autoimmune disease like lupus or rheumatoid arthritis
• Chronic infections or frequent illness
• Cancer, especially blood cancers
• Kidney or liver disease
• Inflammatory bowel disease
• Taking certain medications

Some people have naturally higher or lower sed rates without any underlying disease. This is why your doctor looks at trends over time rather than relying on a single test result.

Is it better to have high or low sed rate?

Generally speaking, a normal or low sed rate is better than a high one, since elevated values usually indicate inflammation or other health problems. However, the "best" sed rate for you depends on your individual circumstances.

A normal sed rate suggests you don't have significant inflammation in your body, which is typically a good sign. Low values are usually even better, indicating minimal inflammatory activity.

High sed rate isn't automatically bad news, though. Sometimes it helps doctors identify treatable conditions early, leading to better outcomes. The key is understanding what's causing the elevation and addressing it appropriately.

Your doctor cares more about changes in your sed rate over time than any single result. If your sed rate has been stable for years, even if it's slightly elevated, that might be normal for you.

What are the possible complications of high sed rate?

High sed rate itself doesn't cause complications - it's a marker of underlying inflammation rather than a disease. However, the conditions that cause elevated sed rate can lead to serious health problems if left untreated.

Untreated autoimmune diseases can damage joints, organs, and other body systems over time. Conditions like rheumatoid arthritis can cause permanent joint deformity, while lupus can affect your kidneys, heart, and brain.

Serious infections that cause very high sed rates can be life-threatening without prompt treatment. For example, endocarditis (heart infection) can damage heart valves, while sepsis can cause organ failure.

Some cancers that elevate sed rate can spread if not diagnosed and treated early. Blood cancers like multiple myeloma or lymphoma may progress rapidly without appropriate therapy.

The most important thing to remember is that early detection and treatment of these conditions can prevent most complications. This is why your doctor takes elevated sed rate seriously and investigates further.

What are the possible complications of low sed rate?

Low sed rate rarely causes complications because it usually indicates either normal health or specific blood conditions that are managed separately. The test result itself isn't harmful.

However, some conditions that cause low sed rate can have their own complications. Sickle cell disease, for example, can cause painful crises and organ damage, but these problems aren't related to the low sed rate itself.

Polycythemia (too many red blood cells) can increase your risk of blood clots, stroke, or heart attack. Again, the low sed rate is just a marker of this condition, not the cause of complications.

Very rarely, an extremely low sed rate might mask inflammation that's actually present, potentially delaying diagnosis of serious conditions. However, this is uncommon, and doctors use multiple tests to assess inflammation.

In most cases, having a low sed rate is reassuring and doesn't require any special monitoring or treatment beyond addressing any underlying conditions that might be present.

When should I see a doctor for abnormal sed rate?

You should definitely follow up with your doctor if you have abnormal sed rate results, especially if they're significantly elevated or if you're experiencing symptoms that concern you.

Seek medical attention promptly if you have a high sed rate along with symptoms like persistent fever, unexplained weight loss, severe fatigue, joint pain and swelling, or chest pain. These combinations can indicate serious conditions that need immediate evaluation.

Even without symptoms, sed rate values above 100 mm/hr warrant prompt medical attention because they often indicate serious underlying conditions like severe infections, autoimmune diseases, or cancer.

For moderately elevated results (30-100 mm/hr), schedule a follow-up appointment within a few weeks. Your doctor will likely want to repeat the test and possibly order additional tests to determine the cause.

If your sed rate is only slightly elevated and you feel well, don't panic. Many conditions that cause mild elevations are easily treatable, and sometimes the elevation is temporary and resolves on its own.