How the Kidneys Work

Learn how the kidneys work in simple, clear language. Understand what kidneys do, how they filter blood, and why kidney lab tests matter.

How The Kidneys Work

Before jumping into lab numbers and test results, it helps to understand the basics:

What do the kidneys actually do?

This page explains the kidneys in clear, simple language so the rest of your results make more sense.

🧭 What Are the Kidneys?

The kidneys are two small, bean-shaped organs located in your lower back, just below your ribs.

Most people have:

one kidney on the left
one kidney on the right

Each kidney is about the size of your fist — but they do very big jobs.

🔁 The Main Job of the Kidneys

The kidneys are your body’s natural filters.

Their most important task is to:

👉 clean waste and extra fluid out of your blood

But they do much more than just make urine.

Healthy kidneys also help:

balance water in your body
control important minerals
regulate blood pressure
keep bones strong
help make red blood cells

They work constantly, every minute of the day.

🧪 How Filtering Happens

Inside each kidney are about one million tiny filters called nephrons.

Here is a simple version of the process:

Blood flows into the kidneys
Tiny filters remove waste and extra fluid
Cleaned blood returns to the body
Waste leaves as urine

This happens over and over, all day long, without you noticing.

💧 Why Urine Is Important

Urine is the way your body gets rid of:

waste products
extra water
extra salts and minerals

The kidneys decide what your body needs to keep and what it needs to remove. That’s why urine can change color or amount depending on your health and hydration.

❤️ Why Kidneys Matter So Much

Without working kidneys:

toxins would build up
fluid would overload the body
important minerals would become unbalanced

That’s why doctors pay close attention to kidney lab results.

🩺 What Can Affect Kidney Function

Many things can influence how well the kidneys work, including:

diabetes
high blood pressure
dehydration
infections
certain medications
kidney stones
heart problems

Some problems are temporary.
Others develop slowly over many years.

🔬 How Doctors Check the Kidneys

Doctors usually check kidney health with simple tests such as:

GFR / eGFR
Creatinine blood test
BUN test
Urinalysis
Protein in urine

These tests help show how well the kidneys are doing their job.

You don’t need both kidneys to live.

Many people live normal lives with:

one kidney
mildly reduced kidney function
early kidney disease

The kidneys are strong and can adapt — especially when problems are caught early.

❓ Common Questions

Can kidneys heal themselves?
Sometimes. Mild problems can improve if the cause is treated.

Does drinking water help the kidneys?
Yes. Staying hydrated helps kidneys work more easily.

Can you live with one kidney?
Yes. Many people do.

Do kidneys get weaker with age?
Kidney function can slowly decline with age, which is normal for many people.

Drink Your water

🧭 What Usually Happens Next

If a lab test shows a possible kidney issue, doctors often:

repeat the test
check urine tests
review medications
monitor over time

One abnormal result rarely tells the whole story.

Where to Go From Here

If you’re looking at specific test results, these pages can help next:

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