What are the best tests to evaluate for impaired renal (kidney) function?

From the Guidelines

The best tests to evaluate renal function include serum creatinine, estimated glomerular filtration rate (eGFR), and urinalysis, with eGFR being the most accurate assessment of kidney function, as recommended by the 2024 ESC guidelines for the management of elevated blood pressure and hypertension 1. The eGFR calculation uses creatinine levels along with age, sex, and body size to provide a more accurate assessment of kidney function, with values above 90 mL/min/1.73m² considered normal. Some key points to consider when evaluating renal function include:

• Serum creatinine is the most commonly used marker, measuring a waste product filtered by the kidneys, with normal ranges of 0.7-1.3 mg/dL for men and 0.6-1.1 mg/dL for women.
• eGFR is a more accurate assessment of kidney function, and its calculation should preferably use a race-free CKD-EPI equation.
• Urinalysis can detect protein or blood in urine, while urine albumin-to-creatinine ratio helps assess kidney damage by measuring albumin excretion.
• Imaging studies like ultrasound or CT scans may be necessary to evaluate kidney structure in certain cases. These tests are essential because the kidneys silently lose function before symptoms appear, and early detection allows for interventions to slow progression of kidney disease and manage complications, as highlighted in the 2023 Kidney International report 1. It's also important to note that the definition of moderate-to-severe CKD requires an eGFR of <60 mL/min/1.73 m2 or albuminuria of ≥30 mg/g (≥3 mg/mmol), as stated in the 2024 ESC guidelines 1. Overall, a comprehensive evaluation of renal function should include a combination of these tests to provide an accurate assessment of kidney function and detect any potential damage or disease.

From the Research

Evaluation of Renal Function

The best tests to evaluate impaired renal (kidney) function include:

• Glomerular filtration rate (GFR) estimation, which is the best indicator of kidney function 2
• Serum creatinine and urea nitrogen levels, which are useful in assessing renal function, especially when viewed in concert 3
• Creatinine clearance (CCr), which is a useful test, but has some drawbacks 4
• Urinary ratio of albumin (or total protein) to creatinine, which reflects the urinary excretion rate of albumin (or total protein) 5

GFR Estimation Methods

Several equations are available to estimate GFR, including:

• Cockcroft-Gault equation, which tends to overestimate GFR 5
• Modification of Diet in Renal Disease (MDRD) study equation, which can be unreliable for high-normal GFR 5
• Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, which provides higher accuracy in CKD diagnosis 2, 5
• Chronic Renal Insufficiency Cohort (CRIC) study equation, which combines serum creatinine and cystatin C in longitudinal modeling of kidney function 2

Limitations of Renal Function Tests

The tests used to evaluate renal function have some limitations, including:

• Variability in serum creatinine levels 2
• Influence of extra-renal factors on serum urea nitrogen levels 3
• Interassay creatinine differences or unusual levels of creatinine generation (muscle mass) or of renal tubular creatinine secretion, which can bias GFR estimates 5