eGFR from Creatinine and Cystatin C (CKD-EPI 2021)

Methodology

CKD-EPI 2021 creatinine–cystatin C; CKD-EPI 2012 cystatin C

135 × min(Scr/κ,1)^α × max(Scr/κ,1)^−0.544 × min(Scys/0.8,1)^−0.323 × max(Scys/0.8,1)^−0.778 × 0.9961^age × 0.963 [F]; κ 0.7/0.9; α −0.219/−0.144

KDIGO 2024 recommends creatinine–cystatin C eGFR when creatinine-based eGFR is less accurate and GFR affects clinical decisions.

Who it is for

Adults aged 18 and over; standardized cystatin C assay.

Version

1.0.1

How this calculator works

Where the formula comes from

• The 2021 CKD-EPI equations omit race; the creatinine–cystatin C equation was developed in 13 studies (5,352 participants) and validated in 12 studies (4,050).^[1]
• The 2012 CKD-EPI work developed cystatin C-alone and combined equations in 5,352 participants; in validation (1,119 participants) the combined equation performed better than either marker alone.^[2]

The inputs

• The 2021 combined equation is 135 × min(Scr/κ,1)^α × max(Scr/κ,1)^−0.544 × min(Scys/0.8,1)^−0.323 × max(Scys/0.8,1)^−0.778 × 0.9961^age × 0.963 if female, with κ 0.7/0.9 and α −0.219/−0.144 (female/male).^[1]
• The 2012 cystatin C equation is 133 × min(Scys/0.8,1)^−0.499 × max(Scys/0.8,1)^−1.328 × 0.996^age × 0.932 if female.^[2]

Where accuracy falls (published evidence)

• KDIGO 2024 notes that cystatin C's non-GFR determinants are less well understood but thought to include higher adiposity, smoking, hypo- and hyperthyroidism, glucocorticoid excess and chronic inflammation.^[3]

What guidelines say

• KDIGO 2024 recommends creatinine–cystatin C eGFR when creatinine-based eGFR is less accurate and GFR affects clinical decisions (grade 1C).^[3]
• Where more accurate GFR would change treatment, KDIGO advises measuring GFR with an exogenous filtration marker.^[3]

Sources

1. Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737–1749. doi:10.1056/NEJMoa2102953
2. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29. doi:10.1056/NEJMoa1114248
3. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314. doi:10.1016/j.kint.2023.10.018

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on 2026-10-12

Worked example: how to calculate eGFRcr-cys

Calculation:

135 × 1.111^−0.544 × 1.25^−0.778 × 0.9961^50 = 135 × 0.9443 × 0.8406 × 0.8225 = 88.14; 133 × 1.25^−1.328 × 0.996^50 = 133 × 0.7436 × 0.8184 = 80.94

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

• A G1 or G2 value alone does not mean kidney disease: CKD also needs markers such as albumin in the urine, lasting more than 3 months.
• Cystatin C may be influenced by non-GFR factors, including higher adiposity, smoking, hypo- and hyperthyroidism, glucocorticoid excess and chronic inflammation (KDIGO 2024).

References

1. Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737–1749. doi:10.1056/NEJMoa2102953
2. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314. doi:10.1016/j.kint.2023.10.018
3. Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20–29. doi:10.1056/NEJMoa1114248