# eGFR Calculator

> Estimates glomerular filtration rate from serum creatinine, age and sex with the CKD-EPI 2021 race-free creatinine equation, and assigns the KDIGO GFR category (G1–G5).

- Calculator id: `egfr` · Category: Medical & Clinical (`medical`) · Tool name: `calculate_egfr`
- Canonical page: https://tttkmbb.com/medical/egfr · This document: https://tttkmbb.com/medical/egfr.md · JSON definition: https://tttkmbb.com/medical/egfr.json

## Purpose

Estimates glomerular filtration rate from serum creatinine, age and sex with the CKD-EPI 2021 race-free creatinine equation, and assigns the KDIGO GFR category (G1–G5).

**Use when:** You have an adult's serum creatinine (mg/dL or µmol/L), age and sex and need an eGFR in mL/min/1.73 m² or its CKD stage.

**Do not use when:** The person is under 18 (paediatric equations differ), creatinine is not in steady state (acute kidney injury), or you need drug-dosing clearance in mL/min (use creatinine-clearance).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `creatinine` | number |  | required | Serum creatinine in the unit given by creatinine_unit. (> 0, max 4000) |
| `creatinine_unit` | enum: mg_dl \| umol_l |  | optional, default "mg_dl" | Unit of the serum creatinine value (1 mg/dL = 88.4 µmol/L). |
| `age_years` | number | years | required | Age in years (adults only). (min 18, max 120) |
| `sex` | enum: male \| female |  | required | Sex used to select the formula coefficients or thresholds. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `egfr_ml_min_1_73m2` | number | mL/min/1.73 m² | Estimated GFR by CKD-EPI 2021 (creatinine), indexed to 1.73 m² body surface area. |
| `ckd_stage` | string |  | G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15 mL/min/1.73 m². |
| `stage_description` | string |  | KDIGO wording for the GFR category. |
| `creatinine_mg_dl` | number | mg/dL | Creatinine used in the equation, in mg/dL. |
| `creatinine_umol_l` | number | µmol/L | Same creatinine in µmol/L (× 88.4). |

## Formula

`eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age_years × 1.012 (if female); κ = 0.7 (female) / 0.9 (male); α = −0.241 (female) / −0.302 (male); Scr in mg/dL (µmol/L ÷ 88.4)`

CKD-EPI 2021 removes the race coefficient of the 2009 equation; a CKD stage requires the eGFR to persist for more than 3 months and is less reliable at extremes of muscle mass, in pregnancy or with unstable creatinine. Results are informational only and not a substitute for clinical judgement or medical advice.

## Data Sources

- National Kidney Foundation – CKD-EPI Creatinine Equation (2021) — https://www.kidney.org/professionals/ckd-epi-creatinine-equation-2021 (standard, retrieved 2026-09-24)
- Inker LA et al. (2021) New creatinine- and cystatin C-based equations to estimate GFR without race, N Engl J Med 385:1737-1749 — https://pubmed.ncbi.nlm.nih.gov/34554658/ (peer_reviewed, retrieved 2026-09-24)
- NIDDK – Estimated Glomerular Filtration Rate Calculators — https://www.niddk.nih.gov/health-information/professionals/clinical-tools-patient-management/kidney-disease/laboratory-evaluation/estimated-gfr-calculators (government, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/egfr?creatinine=…&age_years=…&sex=…`
- `POST https://tttkmbb.com/api/v1/calculate/egfr` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/egfr · OpenAPI operationId `calculate_egfr` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "egfr", "inputs": {…}}`

## Example

- Female, 55 years, creatinine 1.2 mg/dL: inputs `{"creatinine":1.2,"creatinine_unit":"mg_dl","age_years":55,"sex":"female"}` → `{"egfr_ml_min_1_73m2":53.5,"ckd_stage":"G3a","creatinine_umol_l":106}`
- Male, 40 years, creatinine 0.9 mg/dL: inputs `{"creatinine":0.9,"age_years":40,"sex":"male"}` → `{"egfr_ml_min_1_73m2":110.7,"ckd_stage":"G1"}`
- Female, 70 years, creatinine 106 µmol/L: inputs `{"creatinine":106,"creatinine_unit":"umol_l","age_years":70,"sex":"female"}` → `{"egfr_ml_min_1_73m2":48.7,"ckd_stage":"G3a","creatinine_mg_dl":1.2}`

```
GET https://tttkmbb.com/api/v1/calculate/egfr?creatinine=1.2&creatinine_unit=mg_dl&age_years=55&sex=female
```

## Limitations

The person is under 18 (paediatric equations differ), creatinine is not in steady state (acute kidney injury), or you need drug-dosing clearance in mL/min (use creatinine-clearance). CKD-EPI 2021 removes the race coefficient of the 2009 equation; a CKD stage requires the eGFR to persist for more than 3 months and is less reliable at extremes of muscle mass, in pregnancy or with unstable creatinine. Results are informational only and not a substitute for clinical judgement or medical advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why does the result differ from an older lab report?**

Reports before 2021–2022 often used the CKD-EPI 2009 or MDRD equations with a race coefficient; the 2021 equation gives somewhat higher values for Black adults and slightly lower values for others.

**Can I use it for drug dosing?**

Most dosing tables are based on Cockcroft-Gault creatinine clearance in mL/min, not BSA-indexed eGFR; use creatinine-clearance, or de-index eGFR by multiplying by BSA/1.73.

## Related

- [Creatinine Clearance Calculator](https://tttkmbb.com/medical/creatinine-clearance.md) — Cockcroft-Gault clearance in mL/min for drug dosing.
- [Body Surface Area Calculator](https://tttkmbb.com/health/body-surface-area.md) — De-index eGFR to the person's actual BSA.