· Lee Chee Cheow, M.Sc. Dip CMP · Kidney Health · 5 min read
Understanding Your Kidney Numbers: What eGFR and CKD Stages Actually Mean
Your latest blood test probably had an eGFR number on it. Here's what that figure actually measures, how the five CKD stages are defined, and why so many people reach an advanced stage without ever feeling unwell.
If you’ve had a routine blood panel in the last few years, there’s a good chance it included a number labelled eGFR. Most people skim past it. But this single figure is how doctors worldwide define, stage, and track chronic kidney disease (CKD) — a condition that, by some estimates, affects roughly 1 in 7 adults globally without most of them knowing it.
Here’s what the number means, how the five stages work, and why kidney disease is so often silent until it isn’t.
What eGFR actually measures
eGFR stands for estimated glomerular filtration rate — a calculated estimate of how well your kidneys are filtering waste and excess fluid out of your blood. Inside each kidney, blood passes through millions of tiny filtering units. Blood enters through an arteriole, passes through a network of capillaries called the glomerulus, and is filtered into a structure called Bowman’s capsule. From there the kidney reabsorbs what the body still needs, secretes additional waste products, and excretes the rest as urine. In simple terms: excretion equals filtration minus reabsorption plus secretion.
eGFR converts that filtering process into a single number, expressed in mL/min/1.73m². According to the widely used National Kidney Foundation definition, chronic kidney disease is generally defined as an eGFR below 60 mL/min/1.73m² that persists for three months or more, or persistent markers of kidney damage — most commonly albumin (protein) appearing in the urine, known as albuminuria — even if eGFR itself is still in a normal range.
It’s worth remembering, too, that the kidneys do far more than filter waste. They help regulate blood pressure and fluid balance, maintain the body’s acid-base balance, produce the hormone erythropoietin that drives red blood cell production, and activate vitamin D for calcium balance. That’s why declining kidney function tends to ripple outward into so many other systems — blood pressure, bone health, and blood counts among them.
The five stages of CKD
Clinicians use a KDIGO (Kidney Disease: Improving Global Outcomes) heat-map that combines eGFR with the degree of albuminuria to assign a risk category, but the eGFR bands themselves map onto five familiar stages:
| CKD Stage | eGFR (mL/min/1.73m²) | General description |
|---|---|---|
| 1 | ≥90 | Normal or high function, but with other evidence of kidney damage |
| 2 | 60–89 | Mild loss of function |
| 3a | 45–59 | Mild-to-moderate loss |
| 3b | 30–44 | Moderate-to-severe loss |
| 4 | 15–29 | Severe loss |
| 5 | <15 | Kidney failure |
The KDIGO risk table then layers in urine albumin-to-creatinine ratio (UACR): normal-to-mildly-increased (under 30 mg/g), moderately increased (30–300 mg/g), and severely increased (over 300 mg/g). Someone with an eGFR in the “normal” Stage 1–2 range but severely increased albuminuria can already sit in a high-risk category — which is exactly why doctors look at both numbers together, not eGFR alone.
Why so many people don’t know they have it
CKD prevalence varies widely by country. Global age-standardised prevalence in adults is estimated at around 14.2% — roughly one in seven people — but country-level estimates in the region cited in recent research range from about 8% in China to over 24% in the Philippines, with Singapore estimated at close to 15%. Despite that scale, CKD is often called a silent disease, and the data backs that up: Stage 1 and Stage 2 typically produce no symptoms at all, or at most occasional foamy or bloody urine. It’s only from Stage 3 onward that more noticeable signs — fatigue, swelling, changes in urination, anaemia — tend to appear, and by Stage 4 and 5 the symptom list grows substantially longer.
That gap between “kidney function is declining” and “I feel unwell” is the central reason routine screening — a simple blood test for eGFR and a urine test for albumin — matters even for people who feel completely fine, particularly if they have any of the common risk factors covered elsewhere on this site, like diabetes, high blood pressure, or a family history of kidney disease.
Frequently asked questions
Is a low eGFR always a diagnosis of chronic kidney disease? Not on its own. CKD is defined by a low eGFR (below 60) or signs of kidney damage such as albuminuria that persist for three months or longer. A single low reading can sometimes reflect a temporary factor like dehydration or an acute illness, which is why doctors typically repeat testing before confirming a diagnosis.
Can eGFR improve over time? It depends on the underlying cause and how early it’s addressed. Some contributors to reduced kidney function — such as poorly controlled blood pressure or blood sugar — can be managed to slow or in some cases partially reverse decline, particularly in earlier stages. Once function has dropped substantially, the focus generally shifts to slowing further loss and managing complications.
What’s the difference between eGFR and the albuminuria test? eGFR estimates how much blood the kidneys are filtering per minute. The urine albumin test checks whether protein is leaking into the urine — a sign the kidney’s filtering units are damaged even if overall filtration rate looks normal. Doctors use both together because either one can be abnormal before the other is.
This article is for general information only and does not constitute medical advice. If you have a diagnosed kidney condition or risk factors for one, consult your doctor about appropriate screening and monitoring.