What Do MEST-C Biopsy Scores Mean in IgA Nephropathy?

When you are diagnosed with IgA nephropathy, your kidney biopsy report may include a MEST-C score (sometimes called the Oxford Classification) ^[1]. This scoring system grades five specific types of tissue changes found in your kidney filters (glomeruli) and surrounding structures ^[1]. It provides your care team with a standardized way to describe the tissue damage. While some of these lesions reflect more active injury and others reflect chronic scarring, the score cannot determine reversibility or guarantee a response to specific treatments by itself ^[2][3].

Importantly, the MEST-C score is not a single total number that you add up (like a grade out of 10), nor is it a disease stage. Instead, it is a profile of five separate categories. For example, a report might read M0 E1 S1 T0 C0, which provides a descriptive snapshot of your kidney tissue.

Decoding the MEST-C Thresholds

Each letter in the MEST-C acronym represents a different type of structural change. The numbers (0, 1, or 2) indicate the presence or extent of that specific change ^[4][5].

M: Mesangial Hypercellularity

The mesangium is the central stalk that supports your kidney’s filtering capillaries. Mesangial hypercellularity means there are too many cells crowding this supporting area ^[6]. This extra cell growth is associated with a faster decline in kidney function in long-term studies ^[3].

• M0: Half or less (≤0.5) of the glomeruli have this extra cell crowding ^[4].
• M1: More than half (>0.5) of the glomeruli show this extra cell crowding ^[4].

E: Endocapillary Hypercellularity

Endocapillary hypercellularity occurs when extra cells build up inside the capillary loops (the tiny blood vessels in the filters), narrowing the spaces where blood normally flows ^[7]. This finding may prompt discussions about active disease, but it does not independently dictate therapy ^[5][7].

• E0: Absent (no extra cells inside the capillary loops) ^[5].
• E1: Present (extra cells are narrowing the capillary loops in at least some glomeruli) ^[5].

S: Segmental Sclerosis or Adhesion

Segmental sclerosis refers to localized scarring that affects only a part (segment) of a kidney filter, while an adhesion is an abnormal attachment of the filter to its surrounding capsule ^[8]. These findings are grouped together because both indicate areas of permanent damage rather than active inflammation ^[3].

• S0: Absent (neither segmental scarring nor adhesions are seen) ^[5].
• S1: Present (segmental scarring or an adhesion is present in at least one glomerulus) ^[5].

T: Tubular Atrophy and Interstitial Fibrosis

This measures damage to the kidney tubules (which help balance your body’s fluids) and the surrounding structural tissue. Tubular atrophy refers to the shrinking of these tubes, and interstitial fibrosis is the chronic scarring that replaces healthy tissue ^[9]. The T score is consistently one of the strongest predictors of long-term kidney survival ^[9][3]. It is measured as a percentage of the cortical tissue (the outer layer of the kidney).

• T0: 25% or less (≤25%) of the cortical tissue is affected by scarring or atrophy ^[10].
• T1: More than 25% up to 50% (>25% to ≤50%) of the tissue is affected ^[4][10].
• T2: More than 50% (>50%) of the tissue is scarred or atrophied, indicating significant chronic damage ^[4].

C: Cellular or Fibrocellular Crescents

Crescents are moon-shaped collections of cells that form in the space surrounding the kidney filters following glomerular injury ^[11]. They can be cellular (mostly active inflammatory cells) or fibrocellular (a mix of cells and fibrous scar tissue) ^[11]. They were added to the original MEST score in 2016 ^[11][1].

• C0: No crescents present ^[11].
• C1: Crescents are found in less than 25% of the glomeruli ^[11].
• C2: Crescents are found in 25% or more of the glomeruli ^[11].

While higher crescent scores (C1 or C2) are associated with a higher risk of poor kidney outcomes in studies, they do not by themselves diagnose an emergency or dictate specific treatments ^[2][11].

The Impact of Biopsy Specimen Quality

The accuracy of your MEST-C score depends heavily on the quality and size of the biopsy sample ^[12]. Pathologists generally state that the tissue sample should contain a minimum of 8 glomeruli to apply the Oxford Classification ^[12][1]. However, having 8 glomeruli does not guarantee perfect reliability; even an adequate sample can miss localized, focal damage ^[12].

Interpreting kidney biopsies also requires human judgment. Studies show that when multiple pathologists look at the same biopsy, they sometimes disagree on the scoring—particularly for the M, E, and C categories—especially if the damage affects only a small percentage of the tissue ^[13].

Not a Standalone Prescription

While scores like T1/T2, S1, and C1/C2 are associated with a higher risk of kidney function decline, the MEST-C score is never used in a vacuum ^[4][14]. Your doctor will combine these microscopic findings with your clinical signs, such as how much protein is in your urine (proteinuria) and how well your kidneys are filtering waste (estimated glomerular filtration rate, or eGFR) ^[15][16].

Optimized supportive care—such as strict blood pressure control and medications that protect the kidneys—is the foundation of treatment for everyone with IgA nephropathy ^[17][18]. A specific MEST-C profile does not automatically mean you will benefit from immunosuppressive medications (drugs that calm the immune system, like steroids) ^[19][20]. Treatment decisions always require a full view of your clinical risk profile, not just your biopsy report ^[18].