Ordering Kidney Function Tests for Assessment
Yes, you can and should order kidney function tests for assessment—specifically serum creatinine with calculated eGFR and a urine albumin-to-creatinine ratio (UACR)—as these are the recommended initial tests for evaluating kidney function and detecting chronic kidney disease. 1, 2
Initial Testing Approach
Order these two tests together for comprehensive kidney assessment:
- Serum creatinine with eGFR calculation using the CKD-EPI equation (preferably the 2021 race-free version) to assess glomerular filtration rate 1, 2
- Random spot urine albumin-to-creatinine ratio (UACR) rather than dipstick testing, as UACR provides quantitative assessment and superior sensitivity for detecting early kidney damage 1, 2
These two tests provide independent prognostic information and are both required for proper diagnosis and staging of chronic kidney disease. 2
When to Order These Tests
Screen patients with any of these risk factors: 2, 3, 4
- Diabetes mellitus (present in 48% of CKD patients) 1, 2
- Hypertension (present in 91% of CKD patients) 1, 2
- Age >60 years 1, 4
- Cardiovascular disease 1, 4
- Family history of kidney disease 1, 4
- Obesity 1, 4
For patients with diabetes or hypertension, annual screening is recommended. 1, 2
Additional Testing When Needed
If eGFR based on creatinine alone may be inaccurate, measure cystatin C and calculate eGFRcr-cys for more accurate assessment. 1 This is particularly important in patients with:
- Extremes of muscle mass 1
- Malnutrition 1
- Amputation 1
- Situations where creatinine-based estimates are less reliable 1
Interpreting Results and Follow-Up
CKD is diagnosed when either eGFR <60 mL/min/1.73 m² OR UACR ≥30 mg/g persists for at least 3 months, as a single abnormal measurement may reflect acute kidney injury rather than chronic disease. 1, 2
Basic laboratory testing should also include: 1
- BUN/creatinine 1
- Urinalysis 1
- Complete blood count, liver function tests, alkaline phosphatase, and calcium at physician discretion 1
Common Pitfalls to Avoid
Do not rely on serum creatinine alone, as it grossly overestimates kidney function—patients can maintain seemingly normal creatinine levels (e.g., 1.3 mg/dL) despite significantly declining GFR. 1
Do not use 24-hour creatinine clearance for routine assessment, as it is less accurate than eGFR equations, fraught with collection errors, and highly inconvenient for patients. 1
Ensure repeat testing to confirm chronicity before diagnosing CKD, as duration of kidney abnormalities must be ≥3 months to distinguish from acute kidney injury. 1