How to assess kidney function in outpatient clinics

Area of Science:

• Nephrology
• Clinical Chemistry
• Primary Care Medicine

Background:

• A 2002 reclassification defined chronic kidney disease (CKD) using a glomerular filtration rate (GFR) below 60 ml/min/1.73 m(2) for over three months, regardless of other kidney damage indicators.
• This definition necessitates reliable methods for assessing kidney function, particularly in outpatient and primary care settings.

Purpose of the Study:

• To review and discuss various methods for evaluating kidney function in outpatient clinics, with a specific focus on primary care.
• To highlight the evolution and application of estimated glomerular filtration rate (eGFR) equations in diagnosing and managing chronic kidney disease.

Main Methods:

• A comprehensive literature search was conducted using the PubMed database to identify relevant studies and articles.
• The review focused on the development and validation of equations for estimating glomerular filtration rate (eGFR).

Main Results:

• Estimated GFR (eGFR) equations incorporating plasma creatinine, age, sex, race, and body size improve the identification of CKD patients who might be missed by creatinine measurements alone.
• Cystatin C-based equations offer enhanced accuracy for specific patient groups where creatinine-based eGFR is less reliable.

Conclusions:

• The choice of diagnostic test for kidney function assessment can be influenced by patient characteristics, leading to ongoing debate about the optimal method for the general population.
• The CKD-EPI creatinine equation is generally sufficient for estimating renal function in most primary care patients. The CKD-EPIcr-cys equation provides additional accuracy for eGFR values between 45-59 ml/min/1.73 m(2), but its widespread use is limited by the cost of cystatin C analysis.