What tests can be used to evaluate kidney function in someone with one kidney?

Kidney Function Tests for Someone with One Kidney

For someone with one kidney, the recommended approach to evaluate kidney function is to use creatinine-based estimated glomerular filtration rate (eGFRcr) as the initial test, with additional testing such as cystatin C-based measurements when more accuracy is needed. 1

Primary Assessment Methods

• Creatinine-based eGFR (eGFRcr): This should be the first-line test for evaluating kidney function in individuals with a single kidney 1
• Albumin-to-creatinine ratio (ACR): Should be measured to assess for kidney damage through albuminuria, which is a strong predictor of both kidney disease progression and cardiovascular risk 1
• Cystatin C-based measurements: When greater accuracy is needed or when creatinine-based estimates may be unreliable, eGFRcr-cys (combining creatinine and cystatin C) provides better assessment 1

When to Consider Additional Testing

• When eGFRcr may be inaccurate: In cases of altered muscle mass, which may be particularly relevant in patients with a single kidney who might have different metabolic profiles 1
• For clinical decision-making: When treatment decisions depend on precise kidney function assessment 1
• For monitoring progression: To accurately track changes in kidney function over time, especially important with only one functioning kidney 1

Advanced Testing Options

• Measured GFR (mGFR): Using exogenous filtration markers when the highest accuracy is required for clinical decision-making 1
• Timed urine collections: For measured creatinine clearance if mGFR is unavailable and eGFRcr-cys is thought to be inaccurate 1
• Imaging studies: Ultrasound to assess kidney size, shape, and structure, which may be particularly important for a solitary kidney 1

Establishing Chronicity and Monitoring

• Repeat testing: To confirm the presence of chronic kidney disease (CKD) and establish a baseline for the single kidney 1
• Regular monitoring: More frequent assessment may be warranted compared to individuals with two kidneys, as changes in function may have greater clinical significance 1
• Assessment of trends: Changes in eGFR over time are more informative than single measurements, especially in someone with one kidney 1

Common Pitfalls and Caveats

• Overreliance on serum creatinine alone: Using serum creatinine without an estimating equation can lead to significant errors in assessing kidney function 1
• Misinterpretation of normal creatinine levels: Patients with a single kidney may maintain normal serum creatinine despite reduced total GFR 2, 3
• Failure to consider non-GFR determinants: Factors like muscle mass, diet, and medications can affect creatinine levels independent of kidney function 1
• Assuming chronicity based on a single measurement: A single abnormal eGFR or ACR could reflect acute changes rather than chronic disease 1

Testing Algorithm for Single-Kidney Patients

1. Initial assessment: Measure serum creatinine and calculate eGFRcr 1
2. Assess for kidney damage: Measure urine albumin-to-creatinine ratio (ACR) 1
3. If greater accuracy needed: Add cystatin C measurement and calculate eGFRcr-cys 1
4. If still uncertain or for critical decisions: Consider measured GFR using exogenous filtration markers 1
5. For monitoring: Establish regular testing intervals based on baseline function and risk factors 1

By following this comprehensive approach to kidney function assessment in individuals with one kidney, clinicians can accurately monitor kidney health and make appropriate clinical decisions to preserve the function of the remaining kidney.