Henoch-Schonlein purpura, also called IgA vasculitis, is a condition where small blood vessels in the body become inflamed and start to leak. This leads to a characteristic rash, and sometimes affects the joints, belly, and kidneys. Knowing when to seek medical attention and understanding how doctors identify this condition can help families navigate the diagnostic process with confidence.

Introduction: Who Should Undergo Diagnostics

People who notice a distinctive rash that looks like small bruises or purplish-red spots on the skin should consider seeking medical evaluation. This rash, which does not fade when pressed with a glass, typically appears on the legs and buttocks, though it can also show up on the arms, face, chest, back, and belly. The spots may look like blood under the skin and can sometimes be raised to the touch, giving them a bumpy or palpable quality.^[1]

Parents should bring children to see a doctor if the rash is accompanied by other symptoms. Joint pain and swelling, particularly in the knees and ankles, often develop around the same time as the skin changes. Belly pain is another common complaint that warrants attention, especially if it is severe or accompanied by vomiting or blood in the stools. It is especially important to seek urgent medical care if a rash that does not fade when pressed appears alongside feeling very unwell, such as having difficulty looking at bright lights or experiencing a stiff neck, as these could indicate something more serious like meningitis.^[4]

Adults who develop these symptoms should also see a healthcare provider promptly. Although Henoch-Schonlein purpura is much more common in children, particularly those between the ages of 3 and 10, adults can get it too. In fact, the condition tends to be more severe in adults, with a higher chance of lasting kidney problems. Anyone who notices blood in their urine or develops high blood pressure alongside the rash should seek medical attention without delay.^[6]

Long-term follow-up is important even after the initial symptoms have gone away. About half of children who have had Henoch-Schonlein purpura will experience it again, though these repeat episodes are usually less severe than the first one. Regular check-ups help catch any kidney problems early, as kidney damage from this condition can sometimes appear weeks or months after the rash first develops.^[2]

Classic Diagnostic Methods

Henoch-Schonlein purpura is primarily a clinical diagnosis, which means doctors can often identify it based on the symptoms and physical examination without needing extensive testing. The most distinctive feature is the rash itself, which appears in 100% of cases. However, the rash is not always the first symptom to appear. Sometimes joint pain develops one to two weeks before the skin changes become noticeable, which can initially confuse the picture.^[1]

During a physical examination, the doctor will look carefully at the rash and check where it appears on the body. The spots are usually symmetrical, meaning they appear on both sides of the body in similar patterns. They tend to concentrate in areas where gravity or pressure affects the skin most, such as the sock line or waistband. In young children who are not yet walking, the rash may appear on the face or trunk, while older children and adults typically see it on the lower legs and buttocks.^[23]

The doctor will also examine the joints, feeling for warmth and swelling. The large joints of the lower limbs are most commonly affected, though the hands and elbows can be involved too. The belly will be checked for tenderness or signs of more serious complications. Blood pressure measurement is essential at the initial visit and should be repeated at follow-up appointments, as high blood pressure can be a sign of kidney involvement.^[18]

One of the most important diagnostic tests is urinalysis, which checks the urine for blood and protein. This simple test can reveal kidney involvement even when there are no symptoms. Kidney problems from Henoch-Schonlein purpura are often silent, meaning people do not feel anything unusual, but the urinalysis can detect microscopic amounts of blood or protein that indicate the kidneys are being affected. This test should be done at the first visit when Henoch-Schonlein purpura is suspected and repeated regularly during follow-up visits for at least six months.^[23]

If the diagnosis is unclear based on symptoms alone, blood tests may be performed to rule out other conditions. These tests are not used to confirm Henoch-Schonlein purpura directly, but rather to eliminate other possibilities that might look similar. For instance, a complete blood count can show whether the number of platelets in the blood is normal, which helps distinguish Henoch-Schonlein purpura from conditions that cause low platelet counts. Blood tests can also check how well the kidneys are functioning by measuring substances like creatinine and checking protein levels in the blood.^[11]

In cases where there is significant kidney involvement, such as high blood pressure, visible blood in the urine, or substantial protein in the urine, additional tests may be needed. A formal urine microscopy provides a more detailed look at the urine under a microscope. The urinary protein-creatinine ratio measures exactly how much protein is being lost in the urine, which helps doctors assess the severity of kidney damage.^[23]

Imaging studies may be ordered if there are concerns about complications. An ultrasound of the belly can help rule out other causes of abdominal pain and can check for serious problems like bowel obstruction. This test uses sound waves to create pictures of the internal organs and is painless and safe. If severe belly pain is present, ultrasound can help identify complications like intussusception, which is an abnormal folding of the bowel that can cause a blockage and may require surgery.^[11]

A skin biopsy is rarely needed but can be performed if the diagnosis remains uncertain. During this procedure, a small sample of skin is removed and examined under a microscope in a laboratory. People with Henoch-Schonlein purpura have a specific type of protein called immunoglobulin A or IgA deposited in the blood vessels of the affected skin. Special staining techniques called direct immunofluorescence can detect this IgA in the biopsy sample, confirming the diagnosis. However, because the clinical presentation is usually quite characteristic, most people do not need a biopsy.^[11]

When kidney involvement is severe, a kidney biopsy may be recommended. This involves taking a small sample of kidney tissue using a needle guided by ultrasound. The tissue is then examined under a microscope to see how badly the kidneys are damaged and what type of changes are present. This information helps doctors decide on the best treatment approach and gives insight into the likely course of the disease. The IgA deposits can also be seen in the kidney tissue, similar to what appears in the skin.^[5]

Additional tests may be ordered to look for possible triggers or to rule out similar conditions. Since Henoch-Schonlein purpura often follows a respiratory infection, doctors might test for recent infections. Blood tests can check for antibodies against Group A streptococcus bacteria, which is a common trigger. Tests for other infections like parvovirus or Epstein-Barr virus might also be done if the history suggests a recent illness.^[3]

If the symptoms are unusual or if the diagnosis is not straightforward, doctors may order tests to look for other types of vasculitis, which is inflammation of blood vessels. These tests might include checking for specific antibodies like ANCA (anti-neutrophil cytoplasmic antibodies), ANA (antinuclear antibodies), or measuring levels of complement proteins like C3 and C4. These help distinguish Henoch-Schonlein purpura from other vasculitis conditions that might need different treatments.^[23]

Diagnostics for Clinical Trial Qualification

When people with Henoch-Schonlein purpura are being considered for enrollment in clinical trials, more structured and standardized diagnostic criteria are typically used. Clinical trials need to ensure that all participants truly have the condition being studied, so they rely on well-defined inclusion and exclusion criteria based on established classification systems.

Clinical trials often use classification criteria that require the presence of purpura as a mandatory feature, since this rash appears in all cases of Henoch-Schonlein purpura. Additionally, at least one or more of the following must be present: joint pain or arthritis, abdominal pain, or evidence of kidney disease. The rash must be palpable, meaning it can be felt as raised spots on the skin, and it should not be due to low platelet counts, which would be ruled out by a blood test.^[3]

For research purposes, confirmation of IgA deposits is often required. This means that participants may need to undergo a skin biopsy with direct immunofluorescence testing to demonstrate the presence of IgA in the blood vessel walls. This provides objective evidence of the disease mechanism and helps ensure that all study participants have true Henoch-Schonlein purpura rather than a different condition that looks similar.^[10]

Kidney involvement is carefully assessed in clinical trials because it is the most important factor affecting long-term outcomes. Participants will have detailed kidney function tests including blood tests to measure creatinine and estimated glomerular filtration rate, which indicate how well the kidneys are filtering waste from the blood. Urine tests will measure both the amount of blood and protein being lost, often using the urinary protein-creatinine ratio for precision. Blood pressure measurements are taken at multiple time points to detect hypertension.^[13]

Some clinical trials specifically focus on people with kidney involvement and may require a kidney biopsy before enrollment. The biopsy results are examined according to standardized classification systems that grade the severity of kidney damage. This information helps researchers group participants by disease severity and track whether treatments are working. The microscopic examination looks at the kidney tissue for signs of inflammation, scarring, and the presence of IgA deposits.^[14]

Clinical trials will also carefully document all symptoms and their timing. This includes recording when the rash first appeared, when other symptoms developed, and whether this is a first episode or a recurrence of the disease. The severity and extent of the rash may be photographed and measured. Joint involvement is assessed by physical examination and sometimes by imaging if swelling is significant. Abdominal symptoms are documented in detail, and imaging studies like ultrasound or CT scans may be performed to check for complications.^[16]

Blood tests in clinical trials often include markers of inflammation such as C-reactive protein and erythrocyte sedimentation rate, which indicate how active the inflammation is in the body. Tests for IgA levels in the blood may also be performed. Some studies have found that people with Henoch-Schonlein purpura, particularly those with kidney involvement, may have higher levels of IgA in their blood compared to healthy people.^[16]

Trials may exclude people who have other conditions that could confuse the results. This means ruling out other types of vasculitis, infections that can cause similar rashes, or conditions affecting blood clotting. Comprehensive testing ensures that any effects seen during the trial are truly due to the intervention being studied and not due to another underlying condition.

Follow-up assessments in clinical trials are scheduled at specific intervals and include repeated physical examinations, blood tests, and urinalysis. These serial measurements help researchers understand whether symptoms are improving, staying the same, or worsening over time. They also help identify any side effects from the treatment being studied. Blood pressure, urine protein levels, and kidney function tests are monitored particularly closely because kidney problems can develop or worsen even after other symptoms have resolved.