Can cystatin C (Cystatin C) levels be drawn in a patient with a urethral stent in place?

Cystatin C Measurement in Patients with Urethral Stents

Yes, cystatin C levels can be accurately measured in patients with urethral stents in place, as the presence of a urethral stent does not interfere with cystatin C measurement or its reliability as a marker of kidney function.

Background on Cystatin C

Cystatin C is a low-molecular-weight protein that serves as an alternative biomarker for kidney function assessment. Unlike creatinine, cystatin C has several advantages:

• Produced at a constant rate by all nucleated cells
• Freely filtered by the glomeruli
• Not secreted by renal tubules
• Independent of muscle mass, gender, and age 1
• More sensitive for detecting early kidney dysfunction

Why Cystatin C Can Be Measured With Urethral Stents

Urethral stents do not affect cystatin C measurement for several reasons:

1. Systemic biomarker: Cystatin C is measured in serum/blood, not in urine, so the presence of a urethral stent does not interfere with blood collection or analysis 1

2. No metabolic interference: Unlike some markers, cystatin C levels are not affected by urinary tract instrumentation 1

3. Independent of urinary drainage: Since cystatin C measurement doesn't rely on urine collection or analysis, alterations in urinary flow from stents don't impact its measurement 1

Clinical Considerations When Using Cystatin C

When interpreting cystatin C results in patients with urethral stents, consider:

• Timing of measurement: If the patient has recently undergone stent placement surgery, acute kidney injury may temporarily affect cystatin C levels; consider delaying measurement until at least 2 weeks after any acute illness 1

• Baseline comparison: If possible, compare with pre-stent cystatin C levels to detect any changes in kidney function

• Standardization: Ensure the laboratory uses standardized assays traceable to international reference materials for accurate results 1

Advantages of Using Cystatin C in Patients with Urethral Stents

Cystatin C may be particularly valuable in patients with urethral stents because:

1. Better accuracy: Cystatin C provides more accurate GFR estimation in patients with altered urinary drainage patterns 1, 2

2. Early detection: More sensitive for detecting subtle changes in kidney function that might occur with stent-related complications 3

3. Independent of muscle mass: Particularly useful in elderly or cachectic patients with urethral stents 1

When to Consider Cystatin C Testing in Patients with Stents

Consider cystatin C testing in patients with urethral stents in these scenarios:

• When monitoring for potential nephrotoxicity from medications
• When creatinine-based eGFR is 45-59 ml/min/1.73m² and confirmation of CKD status is needed 1
• In patients where creatinine may be less reliable (elderly, extremes of muscle mass)
• When precise kidney function assessment is needed for medication dosing

Practical Implementation

When ordering cystatin C in patients with urethral stents:

• Request both eGFRcys (cystatin C-based) and eGFRcr-cys (combined creatinine and cystatin C) for the most comprehensive assessment 1
• Use the CKD-EPI cystatin C equation for GFR estimation when available 1
• Remember that cystatin C testing may have limited availability and higher cost than creatinine testing

Conclusion

The presence of a urethral stent does not contraindicate or interfere with cystatin C measurement. In fact, cystatin C may provide a more accurate assessment of kidney function in these patients compared to creatinine-based methods, especially when urinary drainage is altered by the stent.