Blood tests play a critical role in diagnosing Churg-Strauss Syndrome (CSS), also known as Eosinophilic Granulomatosis with Polyangiitis (EGPA). Since CSS is a form of vasculitis that causes inflammation in the blood vessels, affects multiple organs, and is marked by an elevated eosinophil count, blood tests are a key component in assessing inflammation, immune activity, and overall health.
When patients exhibit symptoms consistent with CSS, such as asthma, sinus problems, and skin rashes, doctors often order a variety of blood tests to gather diagnostic information. Let's explore the most common blood tests used in diagnosing and monitoring CSS, and what patients can expect during this process.
One of the hallmark signs of Churg-Strauss Syndrome is an elevated eosinophil count. Eosinophils are a type of white blood cell that helps fight infections, particularly parasitic infections, and plays a role in allergic responses. Normally, eosinophils make up less than 5% of white blood cells. In CSS, eosinophils may exceed 10% or higher, leading to a condition called eosinophilia.
Why it's important: Eosinophilia is often one of the first red flags in identifying CSS, especially in patients who present with asthma or other allergic symptoms. A high eosinophil count can indicate the body's heightened immune response, which is characteristic of CSS. This test helps differentiate CSS from other conditions that may cause similar symptoms but do not involve eosinophilia.
What to expect: A simple blood draw is all that's required to measure eosinophil levels. It's typically part of a complete blood count (CBC), which measures all types of blood cells.
The Complete Blood Count (CBC) is a basic but essential blood test used in diagnosing Churg-Strauss Syndrome. In addition to measuring eosinophils, the CBC evaluates other blood components, such as red blood cells, white blood cells, and platelets. This test provides a snapshot of a patient's overall blood health and immune function.
ANCA stands for antineutrophil cytoplasmic antibodies, a type of autoantibody that attacks certain proteins within the body's neutrophils (another kind of white blood cell). While ANCA testing is commonly used in diagnosing vasculitic diseases, its role in Churg-Strauss Syndrome is somewhat variable.
Why it's important: While not all patients with CSS will test positive for ANCA, a significant proportion (40-60%) do, particularly those with more severe vasculitic involvement. ANCA testing helps doctors confirm the diagnosis and also provides insight into the severity and specific subtype of the disease.
What it reveals: A positive ANCA test, particularly p-ANCA (perinuclear ANCA), is more common in CSS cases that involve the kidneys or peripheral nervous system. A negative result doesn't rule out CSS, but a positive result can strongly support the diagnosis.
What to expect: ANCA testing is done via blood draw. If you test positive for ANCA, your doctor may order further tests to assess organ involvement, particularly the kidneys and nervous system.
CRP and ESR are both inflammatory markers, meaning they measure the level of inflammation in the body. Since Churg-Strauss Syndrome causes vasculitis, inflammation is a key feature of the disease, and these markers can help assess the severity of that inflammation.
CRP: C-Reactive Protein is produced by the liver in response to inflammation. Higher CRP levels indicate more widespread inflammation, which may suggest active disease or a flare-up in CSS.
ESR: Also known as the sed rate, the Erythrocyte Sedimentation Rate measures how quickly red blood cells settle at the bottom of a test tube. Inflammation causes proteins in the blood to clump together, which increases the rate at which red blood cells fall. A high ESR indicates significant inflammation.
Why they matter: Both CRP and ESR are non-specific tests, meaning they don't point to any particular disease, but elevated levels are common in autoimmune conditions like CSS. These tests are particularly useful for tracking disease activity over time. For instance, if your CRP or ESR levels spike, it may indicate a flare-up or worsening inflammation, even if symptoms aren't immediately apparent.
What to expect: Both CRP and ESR tests require a standard blood draw. Your doctor may repeat these tests periodically to monitor your disease activity and response to treatment.
Immunoglobulin E (IgE) is an antibody that plays a key role in allergic reactions. Since Churg-Strauss Syndrome often involves a strong allergic component (especially in the early stages), IgE levels are frequently elevated in CSS patients.
Why it's important: Elevated IgE levels suggest an allergic or hypersensitivity response, which is common in the early stages of CSS. This helps doctors understand the allergic aspect of the disease and guides treatment, particularly in managing asthma and other allergic symptoms.
What to expect: Like the other tests, IgE is measured through a blood draw. Elevated IgE levels are not specific to CSS, as they can also be elevated in allergies or asthma, but when combined with other findings, they support the diagnosis.
A Comprehensive Metabolic Panel (CMP) is often ordered to assess overall organ function, especially the kidneys and liver. Since Churg-Strauss Syndrome can affect various organs, including the kidneys, it's important to evaluate how well these organs are functioning.
Kidney function tests: The CMP includes measurements of creatinine and blood urea nitrogen (BUN), both of which indicate how well the kidneys are filtering waste products from the blood. Vasculitis can damage the kidneys, so monitoring these values is essential.
Liver function tests: The CMP also includes liver enzyme tests, which measure levels of enzymes like ALT and AST. These enzymes can be elevated in liver inflammation, either from the disease itself or from medications used to treat CSS.
Electrolytes: The CMP measures electrolytes (sodium, potassium, calcium), which are important for maintaining balance in the body. Electrolyte imbalances can occur if the kidneys aren't functioning properly, or as a side effect of medications used to treat CSS, such as corticosteroids.
What to expect: The CMP requires a blood draw, and your doctor may order it at regular intervals to monitor how CSS and its treatment are affecting your organs over time.
Blood tests for Churg-Strauss Syndrome are not just a tool for diagnosis—they are also crucial for monitoring the disease over time. Once a diagnosis is made, doctors may order repeat tests to assess how well the treatment is working and whether the disease is under control.
Assessing treatment response: As patients undergo treatment with corticosteroids, immunosuppressants, or other medications, doctors use blood tests to track improvements in eosinophil counts, inflammatory markers (CRP, ESR), and other blood parameters. Reductions in eosinophils or inflammation suggest that the treatment is effectively controlling the disease.
Detecting relapses: Even when symptoms seem to be under control, blood tests can reveal early signs of a relapse or flare-up. An increase in eosinophils, CRP, or ESR could indicate that the disease is becoming active again, prompting adjustments in treatment.