How Does the IgAN Prediction Tool Work, and Is It Accurate?

The International IgA Nephropathy (IgAN) Prediction Tool is a calculator used by doctors to estimate the probability that your kidney disease will progress ^[1]. It was designed for adults with biopsy-proven primary IgA nephropathy. Specifically, it predicts the risk of a “composite outcome” over a specific time period (typically up to 5 to 7 years from your biopsy) ^[1]. This composite outcome means either experiencing a 50% drop in your estimated kidney function (eGFR) from its starting point, or reaching kidney failure (end-stage kidney disease, which requires dialysis or a transplant) ^[2].

While international guidelines recommend the tool as a helpful starting point for risk assessment, it is not perfectly accurate for everyone ^[3]. It provides a probability based on historical data from specific populations—not a personal guarantee of your future ^[4].

What This Tool Can and Cannot Tell You

• Can tell you: How a group of patients with similar test results fared over several years in past historical studies.
• Cannot tell you: Exactly what will happen to your kidneys over your lifetime.
• Important: It is not a stand-alone rule for deciding treatment. Do not start, stop, or change medications based on this score alone.

How the Prediction Tool Works

To generate your risk score, the calculator combines several pieces of information gathered at the time of your diagnosis ^[5].

The Inputs

• Clinical data: Your age, blood pressure, the amount of protein in your urine (proteinuria), and your kidney function (eGFR) ^[1].
• Medications: Whether you were taking specific blood pressure medications called RAS inhibitors (such as ACE inhibitors or ARBs) before your biopsy ^[1].
• Race/Ethnicity: The tool includes versions that factor in broad race/ethnicity categories (originally developed using data from White, Japanese, and Chinese populations) and versions that do not ^[1].
• Biopsy findings (MEST Score): A grading system pathologists use to describe specific types of damage in your kidney tissue ^[1]. It includes:
  • M (Mesangial hypercellularity): Extra cells in the kidney’s filtering units.
  • E (Endocapillary hypercellularity): Swelling and extra cells inside the tiny blood vessels of the filters.
  • S (Segmental sclerosis): Scarring in parts of the filters.
  • T (Tubular atrophy/interstitial fibrosis): Scarring in the tubes and supportive tissue of the kidney.

Because the original tool was designed specifically for use at the time of your biopsy, it should not be used to calculate your risk several years later ^[6]. If your doctor wants to reassess your risk one or two years after your diagnosis, there is a separate post-biopsy version of the tool designed for that specific timeline ^[6][7].

A Probability, Not a Certainty

Seeing a percentage about kidney failure can be frightening, but IgA nephropathy is highly variable. When the tool estimates a 30% risk, for example, it means that among roughly 100 similar patients in a comparable historical population, about 30 might be expected to experience a 50% drop in eGFR or kidney failure over the prediction horizon. The other 70 did not.

Because it is a probability and not a biological destiny, the prediction tool should never dictate your treatment by itself ^[8]. It is meant to be used alongside your doctor’s clinical judgment to help discuss which treatment options best balance expected benefits, side effects, and your personal preferences ^[1].

Limitations: Why It Isn’t Perfect

While the tool is a useful guide, studies comparing its predictions to real-world outcomes have found important limitations.

Calibration and Ethnicity

Race and ethnicity in this calculator are statistical proxies, not biological destinies. The tool includes two versions (with and without race/ethnicity terms) ^[1]. However, when tested in outside groups, the tool sometimes struggles with calibration—meaning the predicted risk doesn’t always match the actual observed risk. For instance, studies have shown it may underestimate the risk for some Korean, Indian, and Colombian Hispanic populations, while overestimating it for others ^[9][10][4]. Your doctor must interpret which version is appropriate for you.

The “Treatment Era” Problem

The tool was built using historical data from patients treated years ago. Medicine has advanced, and newer therapies for IgAN—such as SGLT2 inhibitors, targeted-release budesonide (Nefecon), or endothelin-receptor antagonists—were not factored into the original model. A recent study evaluating patients taking these newer medications found that the tool did not fully model their effects and sometimes overestimated the patients’ risk of progression ^[11]. However, you should never discount a concerning score or delay treatment based on the assumption that newer drugs will automatically lower your personal risk.

Missing Data and Biopsy Interpretation

The tool requires complete information to calculate a valid score. If parts of your MEST score are missing from your pathology report, a valid score may not be calculable, and you should not guess the missing values ^[12]. Furthermore, reading biopsies involves some subjectivity; different pathologists might grade the exact same tissue sample slightly differently, which can change the final calculation ^[12].