eGFR and CKD-EPI 2021: A Practical Guide for Medical Laboratory Technologists

For Medical Laboratory Technologists (MLT), serum creatinine is one of the most frequently tested clinical chemistry parameters. However, creatinine levels alone are often less informative without being translated into eGFR (estimated Glomerular Filtration Rate) — the estimated glomerular filtration rate that serves as the basis for classifying a patient's kidney function.

This article discusses what eGFR is, why the 2021 CKD-EPI equation is now the standard, and how MLTs can assist in interpreting these results accurately.

What is eGFR?

eGFR is an estimated value of how well the kidneys filter blood, expressed in mL/min/1.73m². Because true GFR is difficult to measure directly in routine clinical practice, clinicians use estimation equations based on serum creatinine, age, and sex.

eGFR serves as the primary basis for:

• Determining the stage of Chronic Kidney Disease (CKD)
• Adjusting drug dosages in patients with kidney impairment
• Screening for the risk of chronic kidney disease progression
• Long-term monitoring of patients with diabetes and hypertension

Why CKD-EPI 2021?

Previously, the CKD-EPI (2009) equation included a coefficient based on race (specifically "Black" vs "non-Black" status). This approach drew scientific criticism because race is not a biological variable that directly influences creatinine production — rather, it is an inconsistently applied proxy globally, including in Indonesia.

In 2021, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended the new CKD-EPI 2021 equation, which no longer uses a race variable, basing it only on:

• Serum creatinine (mg/dL)
• Age
• Sex

This approach is now the standard for eGFR reporting in many modern clinical laboratories.

CKD-EPI 2021 Equation (Creatinine)

$$eGFR = 142 \times \min\left(\frac{Scr}{\kappa}, 1\right)^{\alpha} \times \max\left(\frac{Scr}{\kappa}, 1\right)^{-1.200} \times 0.9938^{Age} \times (1.012 \text{ if female})$$

Notes:

Parameter Female Male κ (kappa) 0.7 0.9 α (alpha) -0.241 -0.302 Sex factor ×1.012 ×1 This equation looks complex to perform manually, but it is simple enough to implement as a digital calculation tool — such as the interactive calculator below.

CKD Stage Classification Based on eGFR

According to the 2012 KDIGO guidelines, eGFR results are grouped into the following stages:

Stage eGFR (mL/min/1.73m²) Interpretation G1 ≥ 90 Normal or high G2 60–89 Mildly decreased G3a 45–59 Mildly to moderately decreased G3b 30–44 Moderately to severely decreased G4 15–29 Severely decreased G5 < 15 Kidney failure Important note: complete CKD classification does not depend solely on eGFR, but also considers albuminuria status (categories A1–A3) according to the KDIGO risk matrix.

The Role of MLTs in eGFR Interpretation

Although the final clinical decision rests with the physician, MLTs play a vital role in ensuring the accuracy and reliability of the serum creatinine values that form the basis of the eGFR calculation, including:

• Ensuring daily quality control (QC) of the creatinine method is performed according to Westgard rules
• Verifying the absence of pre-analytical interference (hemolysis, lipemia, icterus) that could affect creatinine results
• Understanding that the reported eGFR value is highly dependent on the precision and accuracy of the creatinine testing method in their respective laboratories

Even the smallest error in creatinine results can impact a patient's CKD stage classification — making laboratory analytical quality the essential foundation behind accurate eGFR.

Important Note

The eGFR calculator in this article is provided for educational purposes and initial estimation. These results do not replace clinical judgment and should always be interpreted in conjunction with a patient's comprehensive clinical data.