CKD-EPI Cystatin C eGFR Calculation (2012 Equation)

eGFR = 133 × min(Scys/0.8, 1)^(-0.499) × max(Scys/0.8, 1)^(-1.328) × 0.996^Age

• Cystatin C = 1.19 mg/L
• Sex = Male
• Age = <40 (using 35 as representative)

1. Scys / 0.8 = 1.19 / 0.8 = 1.4875
2. Since 1.4875 > 1:
   • min(1.4875, 1) = 1 → 1^(-0.499) = 1.0
   • max(1.4875, 1) = 1.4875 → 1.4875^(-1.328) = 0.5825
3. Age factor: 0.996^35 = 0.8691
4. eGFR = 133 × 1.0 × 0.5825 × 0.8691 = ~67.3 mL/min/1.73m²

Result by Age (Male, CysC 1.19 mg/L)

Interpretation

Note: If you need the exact age for a precise result, or if creatinine is also available, the combined CKD-EPI Creatinine-Cystatin C 2021 equation gives greater accuracy (P30 = 90.8%).

CKD-EPI Creatinine-Cystatin C Combined eGFR (2021 Equation)

eGFR = 135 × min(SCr/0.9, 1)^(-0.144) × max(SCr/0.9, 1)^(-0.544) × min(Scys/0.8, 1)^(-0.323) × max(Scys/0.8, 1)^(-0.778) × 0.9961^Age

• Serum Creatinine = 1.2 mg/dL
• Cystatin C = 1.19 mg/L
• Sex = Male
• Age = <40 (using 35)

1. Creatinine terms (κ = 0.9 for male):
   • SCr/κ = 1.2/0.9 = 1.333
   • Since 1.333 > 1:
     • min(1.333, 1) = 1 → 1^(-0.144) = 1.0
     • max(1.333, 1) = 1.333 → 1.333^(-0.544) = 0.8397
2. Cystatin C terms (0.8 threshold):
   • Scys/0.8 = 1.19/0.8 = 1.4875
   • Since 1.4875 > 1:
     • min(1.4875, 1) = 1 → 1^(-0.323) = 1.0
     • max(1.4875, 1) = 1.4875 → 1.4875^(-0.778) = 0.7310
3. Age factor: 0.9961^35 = 0.8724
4. eGFR = 135 × 1.0 × 0.8397 × 1.0 × 0.7310 × 0.8724 = 135 × 0.8397 × 0.7310 × 0.8724 = ~72.2 mL/min/1.73m²

Results Summary

Interpretation

• eGFR ~72 mL/min/1.73m² = CKD Stage G2 (mildly decreased, 60-89 range)
• Both creatinine and cystatin C are mildly elevated above normal, consistent with each other - this concordance increases confidence in the estimate
• Cystatin C-based eGFR is particularly useful as it is less affected by muscle mass, diet, and protein intake than creatinine alone
• To formally diagnose CKD, this finding must persist for >3 months with evidence of kidney damage (albuminuria, hematuria, structural abnormality, or biopsy findings)

Clinical note: With an exact age, the result will shift slightly - roughly +1 mL/min per decade younger than 35. If the patient is, say, 25, eGFR would be approximately ~74-75 mL/min/1.73m², still G2.

CKD-EPI Creatinine + Cystatin C Combined eGFR (2021 Equation)

eGFR = 135 × min(SCr/0.9, 1)^(−0.144) × max(SCr/0.9, 1)^(−0.544) × min(Scys/0.8, 1)^(−0.323) × max(Scys/0.8, 1)^(−0.778) × 0.9961^Age

Step-by-Step Calculation

• SCr/κ = 1.2 / 0.9 = 1.3333
• 1.3333 > 1, so:
  • min(1.3333, 1)^(−0.144) = 1.0^(−0.144) = 1.0
  • max(1.3333, 1)^(−0.544) = 1.3333^(−0.544) = 0.8390

• Scys/0.8 = 1.19 / 0.8 = 1.4875
• 1.4875 > 1, so:
  • min(1.4875, 1)^(−0.323) = 1.0^(−0.323) = 1.0
  • max(1.4875, 1)^(−0.778) = 1.4875^(−0.778) = 0.7310

• 0.9961^27 = 0.8983

eGFR = 135 × 1.0 × 0.8390 × 1.0 × 0.7310 × 0.8983 = 135 × 0.8390 × 0.7310 × 0.8983 = ~74.3 mL/min/1.73m²

Full Comparison (Age 27, Male)

The cystatin C pulls the estimate lower than creatinine alone - which is clinically significant. In a young 27-year-old male (typically higher muscle mass), creatinine tends to overestimate GFR, so the combined equation is the most reliable here.

Interpretation

• Both markers are concordantly elevated, reinforcing the result
• At age 27, an eGFR of 74 warrants follow-up - a healthy 27-year-old typically has eGFR >90
• Check urine albumin-to-creatinine ratio (UACR) - if >30 mg/g, CKD diagnosis can be made even at this eGFR with 3 months persistence
• Consider workup: blood pressure, urinalysis, renal ultrasound, and repeat labs in 3 months

CKD-EPI Creatinine + Cystatin C Combined eGFR (2021 Equation)

• SCr = 0.9 mg/dL | Scys = 1.19 mg/L | Male | Age 26

Step-by-Step Calculation

• SCr/κ = 0.9 / 0.9 = 1.0000
• Exactly at threshold:
  • min(1.0, 1)^(−0.144) = 1.0^(−0.144) = 1.0
  • max(1.0, 1)^(−0.544) = 1.0^(−0.544) = 1.0

• Scys/0.8 = 1.19 / 0.8 = 1.4875
• 1.4875 > 1, so:
  • min(1.4875, 1)^(−0.323) = 1.0^(−0.323) = 1.0
  • max(1.4875, 1)^(−0.778) = 1.4875^(−0.778) = 0.7310

• 0.9961^26 = 0.9015

eGFR = 135 × 1.0 × 1.0 × 1.0 × 0.7310 × 0.9015 = 135 × 0.7310 × 0.9015 = ~88.9 mL/min/1.73m²

Full Comparison (Age 26, Male, SCr 0.9, CysC 1.19)

Interpretation

• Creatinine of 0.9 mg/dL is completely normal in a 26-year-old male → creatinine-only eGFR of ~119 suggests normal kidney function
• Cystatin C of 1.19 mg/L is elevated (normal <1.0) → pulls the combined eGFR down to ~89
• This discordance is clinically important. Cystatin C is not affected by muscle mass, so it can unmask early kidney dysfunction that creatinine misses, especially in:
  • Young muscular males (high muscle mass falsely normalizes creatinine)
  • Early diabetic nephropathy
  • Early hypertensive nephropathy
  • Cardiovascular risk states (CysC is also an independent CV risk marker)

• Urine albumin-to-creatinine ratio (UACR)
• Urinalysis with microscopy
• Blood pressure assessment
• Repeat labs in 3 months to confirm persistence
• Consider causes of isolated CysC elevation: corticosteroid use, thyroid dysfunction, inflammation/CRP elevation (these can falsely raise CysC without true GFR reduction)

hsCRP 4.0 mg/L - Clinical Interpretation

hsCRP Risk Stratification (AHA/CDC)

Why This Matters for This Patient

Clinical Picture

1. Elevated CysC - possibly overestimating kidney dysfunction
2. Elevated hsCRP - marking increased cardiovascular risk
3. The "true" eGFR may be higher than ~89 once inflammation is controlled

• Repeat CysC and hsCRP after treating any underlying inflammatory cause
• UACR (urine albumin-to-creatinine ratio) - key to distinguish true CKD
• Lipid panel - hsCRP 4.0 at age 26 warrants full CV risk assessment
• ANA, ESR - screen for autoimmune/inflammatory condition
• Thyroid function (TSH) - hypothyroidism raises both CysC and hsCRP
• Blood pressure - essential
• BMI/metabolic screen - obesity drives chronic low-grade inflammation
• Rule out acute illness, dental infection, periodontal disease (common cause of elevated hsCRP in young adults)

Bottom line: Do not label this patient as CKD G2 yet. The elevated CysC in the context of hsCRP 4.0 is likely partly or wholly inflammation-driven. Treat the underlying cause, repeat in 6-8 weeks, and reassess. The creatinine being perfectly normal at 0.9 supports this interpretation.