MAPI Score Calculator — Deceased Donor Kidney Biopsy
Use this skill when a procurement biopsy has been performed on a deceased donor kidney (typically a marginal/ECD donor) and an objective histological grading is needed to decide:
- Single kidney transplant (low risk)
- Dual kidney transplant (intermediate risk)
- Discard (high risk)
The Maryland Aggregate Pathology Index (MAPI) is the scoring system recommended by ISOT 2025 for marginal deceased donor kidney evaluation.
STEP 1 — Ensure biopsy adequacy
A reliable MAPI requires:
- Wedge biopsy (preferred) or needle core biopsy with adequate cortex.
- ≥25 glomeruli for valid glomerulosclerosis assessment.
- At least one artery for arteriolar scoring.
- Both kidneys assessed if dual transplant is being considered.
If the biopsy is inadequate → repeat or proceed on clinical grounds alone.
STEP 2 — Score the four histological components
| Component | Finding | Points |
|---|
| Glomerulosclerosis | <15% | 0 |
| 15–20% | 4 |
| >20% | 7 |
| Tubular atrophy | Absent | 0 |
| <50% of cortex affected | 1 |
| ≥50% of cortex affected | 3 |
| Interstitial fibrosis | Absent | 0 |
| Mild (Banff ci1, 6–25%) | 2 |
| Moderate–severe (Banff ci2/ci3, >25%) | 5 |
| Arteriolar narrowing / hyalinosis | Absent | 0 |
| Wall thickening less than the diameter of the lumen | 2 |
| Wall thickening greater than the diameter of the lumen | 4 |
MAPI total = sum of all four components (range 0–19).
STEP 3 — Interpret the score
| MAPI | Risk band | Approximate 5-yr graft survival | Action |
|---|
| <7 | Low | ~90% | ✅ Use as single kidney transplant |
| 7–11 | Intermediate | ~70–80% | ⚠️ Dual kidney transplant (en bloc or paired single) — OR allocate single only to lower-immunological-risk recipient |
| >11 | High | <70% | ❌ Discard, or dual transplant only if recipient has no alternative |
STEP 4 — Combine with clinical context
Histology is one input — combine with:
- Donor age (>70 raises threshold for single use)
- KDRI / KDPI if available
- Cold ischaemia time
- Recipient sensitisation, age, and waiting time
- Macroscopic appearance of kidney (vasculature, parenchyma)
ISOT 2025 guidance: if procurement biopsy is not feasible, base the decision on clinical severity, degree of oliguria, and need for dialysis in the donor.
STEP 5 — Document the decision
Output should include the MAPI score, the four component scores, the risk band, and the allocation decision.
CLINICAL GUARDRAILS
- MAPI is for marginal/ECD donors — not needed for standard criteria donors.
- The score is one tool, not the entire decision — a MAPI of 8 in a 35-year-old donor with brief CIT is very different from MAPI 8 in a 72-year-old after 20 hours of CIT.
- Glomerulosclerosis dominates the score — if >20% globally sclerosed glomeruli, the score is already ≥7 regardless of other components.
- Dual kidney transplant adds technical complexity and anastomosis time — weigh this against the expected graft survival benefit.
- A single reading is operator-dependent — where possible, get a transplant pathologist (not a general pathologist on call) to score.
- AKI changes the picture — see the AKI donor decision skill; tubular injury from AKI can over-inflate the tubular atrophy score on frozen section.
OUTPUT TEMPLATE
DONOR: [age, sex, comorbidities, cause of death, CIT]
BIOPSY: [type, glomerulus count, adequacy]
Glomerulosclerosis: __% → __ points
Tubular atrophy: __ → __ points
Interstitial fibrosis: __ → __ points
Arteriolar narrowing: __ → __ points
MAPI total: __ / 19
Risk band: [Low / Intermediate / High]
Decision: [Single KT / Dual KT / Discard]
Justification: [combine MAPI + clinical context]
SOURCE
Munivenkatappa RB, Schweitzer EJ, Papadimitriou JC, et al. The Maryland aggregate pathology index: a deceased donor kidney biopsy scoring system for predicting graft failure. American Journal of Transplantation 2008;8(11):2316–2324. DOI: 10.1111/j.1600-6143.2008.02370.x
Referenced in: Balwani MR, Kute VB, Shrimali J, et al. ISOT position statement on the feasibility of an organ for transplantation from brain-dead deceased donors: a Delphi consensus. The Lancet Regional Health – Southeast Asia 2025;39:100628 (Supplementary Table S4, marginal donor kidney evaluation).