What does mildly impaired renal function mean?

Understanding Cystatin C 1.08 mg/L

A cystatin C level of 1.08 mg/L indicates mildly impaired renal function, corresponding to an estimated GFR in the range of 45-60 mL/min/1.73 m² (CKD Stage G3a), which represents mild to moderate kidney dysfunction that warrants monitoring and risk factor modification. 1

What This Value Means

• Cystatin C of 1.08 mg/L is elevated above the normal threshold of <1.0 mg/L, indicating reduced glomerular filtration rate even when serum creatinine may still appear normal 1, 2

• This level suggests CKD Stage G3a (GFR 45-59 mL/min/1.73 m²), which is classified as "mildly to moderately decreased" kidney function 1

• Importantly, cystatin C can detect renal impairment earlier than creatinine alone, particularly in patients with normal or near-normal creatinine levels who actually have reduced GFR 1, 3

Clinical Significance and Risk Implications

• Elevated cystatin C (≥1.0 mg/L) is an independent predictor of adverse cardiovascular events, with patients showing significantly higher cardiac event rates (38.7% vs 10.3%) compared to those with normal levels 2

• Even mild renal dysfunction at this level increases cardiovascular risk and requires more intensive risk factor management 1

• This degree of kidney impairment places patients at moderately increased risk for CKD progression according to KDIGO risk stratification 1

Recommended Monitoring and Management

Monitoring frequency: Screen or monitor kidney function 1-2 times per year at this GFR level (Stage G3a) 1

Essential laboratory assessments:

• Measure urinary albumin-creatinine ratio (UACR) to assess for albuminuria, which further stratifies risk 1
• Check serum creatinine and calculate eGFR using MDRD or CKD-EPI equations for comparison 1
• Monitor electrolytes (potassium, bicarbonate), calcium, phosphorus, and parathyroid hormone 4
• Assess hemoglobin and iron studies for anemia of CKD 4

Blood pressure management:

• Optimize blood pressure control to reduce CKD progression risk 1
• If albuminuria is present (UACR ≥30 mg/g), initiate ACE inhibitor or ARB therapy 1

Medication adjustments:

• Review and dose-adjust all renally cleared medications for GFR 45-60 mL/min/1.73 m² 4
• Avoid nephrotoxic agents including NSAIDs, aminoglycosides, and minimize contrast exposure 4

Important Caveats

• Cystatin C levels can be influenced by factors beyond renal function, including age, male gender, greater body weight, current smoking, and elevated C-reactive protein 5

• However, these non-renal factors have minimal clinical impact on the interpretation of elevated cystatin C as a marker of reduced kidney function 5

• In patients with cirrhosis and ascites, cystatin C is particularly useful as serum creatinine often underestimates the degree of renal dysfunction 3

• The combination of elevated cystatin C with normal creatinine should prompt further evaluation, as significant renal impairment may be present despite reassuring creatinine values 1, 3

When to Refer to Nephrology

• Referral is not urgently required at this level of kidney function 4

• Consider nephrology consultation if: GFR continues to decline, albuminuria is present (especially if ≥300 mg/g), difficult-to-control hypertension develops, or unexplained etiology of kidney disease 1

• Urgent nephrology referral becomes necessary only if GFR falls below 30 mL/min/1.73 m² (Stage G4) or if acute kidney injury develops 4