IgA nephropathy diagnosis

IgA nephropathy (IgAN or Berger disease) is a kidney condition marked by the accumulation of an abnormal form of immunoglobulin A (IgA) protein inside the glomeruli, or the filtration units of the kidneys. Over time, these IgA deposits and the body’s immune response against them can lead to kidney disease or failure.

IgAN symptoms are often mild and overlap with those of other kidney conditions. Therefore, an IgA nephropathy diagnosis is usually a multi-step process that requires a kidney biopsy (tissue sample).

What may lead a doctor to suspect IgA nephropathy?

A doctor may begin to suspect IgA nephropathy if a patient has a family history of the disease or if they have a history of blood in their urine (hematuria), especially if the episodes coincide with respiratory infections. Protein in the urine (proteinuria) or a decrease in the estimated glomerular filtration rate (eGFR), a measure of kidney function, might also prompt testing for IgAN.

How is IgA nephropathy diagnosed?

If a doctor suspects that a patient has IgAN, they are likely to test several aspects of the patient’s kidney function before recommending a kidney biopsy for IgA nephropathy.

Medical history and physical examination

During a physical exam, the doctor is likely to ask about recent symptoms, especially changes in urine (such as discolored or foamy urine) and urination habits, as well as medical and family history. They may take the patient’s blood pressure, check for abdominal pain or tenderness, and look for signs of edema (swelling) in the feet, legs, and face, which may indicate reduced kidney function.

Urine tests for blood and protein

Urine tests for IgA nephropathy may include the following:

• Hematuria: Macroscopic hematuria may turn the urine brown, “cola colored,” red, or pink, while microscopic hematuria doesn’t cause visible changes but can be detected using a dipstick test or under a microscope.
• Urine albumin-to-creatinine ratio (uACR) or urine protein-to-creatinine ratio (uPCR): Tests used to measure the amount of protein in urine as compared to creatinine, a normal waste product. uACR measures the amount of albumin, a common protein, while uPCR measures the overall amount of protein.

These tests can usually be run on a single urine sample. In some cases, a doctor may ask a patient to collect their urine for 24 hours to run more specialized tests.

Blood tests to measure kidney function

The standard blood test for kidney function is an eGFR test, which measures how well the kidneys remove waste from the blood. If a doctor is worried about a patient’s kidney function, they may also recommend a measured glomerular filtration rate test, which requires 24-hour urine collection or multiple blood tests.

Why a kidney biopsy is usually needed

A definitive IgAN diagnosis requires a kidney biopsy, because the only conclusive way to test for IgA nephropathy is by examining kidney tissue for abnormal IgA deposits. Current guidelines for doctors recommend a kidney biopsy for most people with proteinuria above a certain threshold.

What happens during a kidney biopsy?

A kidney biopsy is a procedure where a doctor takes a small sample of kidney tissue. Usually, this can be done using a needle biopsy (percutaneous biopsy), where a doctor inserts a needle through the skin into the kidney. If a needle biopsy isn’t an option, a kidney biopsy may require a small surgery. The biopsy sample will be carefully examined under a microscope for IgA deposits and other features.

What the Oxford MEST-C score means

To evaluate kidney tissue for IgAN, a doctor is likely to use a scoring system called the Oxford classification for IgA nephropathy, or MEST-C score. This is a set of criteria used to diagnose IgAN and determine the risk level (how likely the disease is to progress).

The components of this score include the following:

• Cellularity: How many extra cells are inside the glomeruli (hypercellularity)
• Damage: How much scarring or atrophy (wasting) there is inside the glomeruli and the kidneys overall
• Structure: Whether there are “crescents” inside the glomeruli, which are distinctive structures that form when the glomeruli get damaged

Tests used to rule out other conditions

Since the signs and symptoms of IgAN often overlap with those of other kidney conditions, a doctor may run additional tests to rule out other conditions before recommending treatment for IgAN.

Differential diagnoses for hematuria and proteinuria may include the following:

• IgA vasculitis (Henoch-Schönlein purpura): This is a very similar condition that can cause abnormal IgA deposits in the kidneys. IgA vasculitis is more common in children and can usually be distinguished from IgAN based on its symptoms. If a kidney biopsy is performed, it usually shows more inflammatory injury than in IgAN.
• Poststreptococcal glomerulonephritis: This can be distinguished from IgAN based on the timing of symptoms and blood test results.
• Lupus nephritis: This is an autoimmune condition that can attack multiple parts of the body, often including the kidneys. Lupus can be distinguished from IgA nephropathy based on blood tests and the findings on a kidney biopsy.
• Cancer in the kidneys or urethra: A doctor may recommend imaging or other tests to rule out cancer, especially for individuals older than 40.

What happens after a diagnosis?

After an IgAN diagnosis is confirmed, a doctor is likely to discuss prognosis (outcome) and treatment options. Selecting an IgAN treatment depends on factors such as current kidney function, disease risk level, and overall patient health and preferences. Patients should consult with their doctor to determine the most effective treatment plan.

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