Analysis of Chronic Kidney Disease Staging With Different Estimated Glomerular Filtration Rate Equations in Chinese Centenarians

China’s centenarian population is growing faster than ever—by 2050, it’s projected to reach 100,000. But with extreme longevity comes unique health challenges, especially for kidney function. Chronic kidney disease (CKD) is a silent threat in older adults, and accurate diagnosis relies on estimating glomerular filtration rate (eGFR)—a key marker of how well kidneys filter waste. But which eGFR equation works best for people over 100? A 2019 study in the Chinese Medical Journal set out to answer this question, and the results could change how we care for our oldest citizens.

Why eGFR Matters for Centenarians

eGFR measures how much blood your kidneys clean per minute. It’s calculated using formulas that rely on serum creatinine (Scr)—a waste product from muscle metabolism. The three most common equations are:

MDRD (Modification of Diet in Renal Disease): Developed for people with CKD, but not tested in older adults.
CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration): More accurate for mild kidney impairment but unproven in centenarians.
BIS1 (Berlin Initiative Study 1): Designed for adults over 70, but how does it perform in those over 100?

No guidelines exist for which equation to use in centenarians—until now.

The Study: 966 Centenarians From Hainan Province

The research included 966 centenarians (age 100+) from Hainan Province, part of the China Hainan Centenarian Cohort Study (CHCCS)—one of the largest studies of its kind. Researchers:

Collected blood samples to measure Scr, serum uric acid (SUA), and other markers.
Recorded height, weight, blood pressure, and comorbidities (e.g., hypertension, diabetes).
Obtained ethical approval from the Hainan Branch of the Chinese People’s Liberation Army General Hospital.
Secured consent from participants or their family members (for those unable to consent themselves).

Key Results: Which Equations Agree?

The study used two tools to measure agreement between equations:

k-statistic: A score from 0 (no agreement) to 1 (perfect agreement).
Bland-Altman plots: Graphs that show how much two tests disagree.

Here’s what they found:

1. MDRD and CKD-EPI Are Most Consistent

The MDRD and CKD-EPI equations agreed substantially (k=0.61)—meaning they often assigned the same CKD stage. Their average difference in eGFR was just 6 mL/min/1.73m², with 95% of results falling within a “reasonable” range (-14.8 to 26.8 mL/min/1.73m²).

2. BIS1 Disagrees With Both

Agreement between MDRD/BIS1 (k=0.25) and CKD-EPI/BIS1 (k=0.38) was fair at best. BIS1 consistently calculated lower eGFR values than MDRD and CKD-EPI—leading to more diagnoses of advanced CKD.

3. CKD Stages Vary Widely by Equation

When classifying CKD stages (per KDIGO guidelines: Stage 1 = mild/no impairment; Stage 5 = kidney failure), the equations gave drastically different results:

MDRD: 9.7% of centenarians in Stage 1 (far more than CKD-EPI: 0.2% or BIS1: 0.2%).
BIS1: 77.9% in Stage 3 (moderate impairment) and 13.6% in Stage 4 (severe)—way higher than MDRD (47.7% Stage 3, 4.8% Stage 4) or CKD-EPI (54.0% Stage 3, 6.2% Stage 4).
All equations: Stage 5 (kidney failure) was rare (<1.2% of centenarians).

What Drives the Differences?

The study identified three key factors that explained why equations disagreed:

1. Serum Creatinine (Scr)

Scr was the biggest driver of differences. It explained:

10.96% of the gap between MDRD and CKD-EPI.
41.60% of the gap between MDRD and BIS1.
17.06% of the gap between CKD-EPI and BIS1.

Why? Scr is linked to muscle mass—older adults (especially women) often have sarcopenia (muscle loss), which lowers Scr. MDRD and CKD-EPI aren’t designed for low Scr levels, so they overestimate eGFR (making kidney function look better than it is). BIS1, designed for older adults, accounts for this better.

2. Gender

Women had larger differences between MDRD/CKD-EPI and MDRD/BIS1 than men. This aligns with sarcopenia: women lose more muscle as they age, leading to lower Scr and more “false high” eGFR results from non-age-specific equations.

3. Serum Uric Acid (SUA)

SUA (a waste product from purine metabolism) explained 3.65% of the MDRD/CKD-EPI gap and 5.43% of the MDRD/BIS1 gap. High SUA is common in older adults and linked to kidney damage—something the equations may not account for equally.

What This Means for Care

These differences aren’t just academic—they impact treatment decisions. For example:

A centenarian classified as Stage 2 (mild impairment) by MDRD might not get the same monitoring as someone classified as Stage 3 by BIS1.
Stage 3 CKD requires regular checks for complications like anemia or bone disease—something a Stage 2 diagnosis might miss.
BIS1’s higher rate of Stage 4 diagnoses could lead to earlier referrals for dialysis, while MDRD might delay care.

Strengths and Limitations

The study’s biggest strength is its size—966 centenarians is one of the largest samples ever studied. It also used standardized blood tests and strict ethical standards.

But there are limits:

Researchers couldn’t use the “gold standard” GFR test (99mTc-DTPA imaging) because it’s invasive and unsuitable for weak centenarians.
Serum cystatin C (another kidney marker) wasn’t measured due to cost—so the study couldn’t compare cystatin C-based equations.
All participants were from Hainan Province—results may not apply to centenarians in other regions.

Conclusion: We Need a New Equation for Centenarians

The MDRD, CKD-EPI, and BIS1 equations cannot be used interchangeably in centenarians. They give different results, especially for Stages 2 and 3—where treatment decisions matter most.

Scr, gender, and SUA are the biggest drivers of these differences. For example:

An older woman with sarcopenia (low Scr) might have an artificially high eGFR from MDRD, while BIS1 would give a more accurate (lower) number.
A centenarian with high SUA might have hidden kidney damage that MDRD misses but BIS1 catches.

The authors call for a new equation designed specifically for centenarians—one that accounts for their unique physiology (muscle loss, comorbidities, and low Scr). Until then, doctors should:

Consider Scr, gender, and SUA when choosing an equation.
Avoid relying on a single equation—use multiple to get a full picture.

This study was published in the Chinese Medical Journal (2019) by researchers from the Chinese People’s Liberation Army General Hospital, Zhengzhou University, and the Hainan Branch of the PLA General Hospital. The full study can be accessed at doi.org/10.1097/CM9.0000000000000079

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