Understanding the 4 Grades of Hydronephrosis

 If you’ve ever been told you have hydronephrosis, it can sound alarming. But not every case means your kidneys are in danger. In this blog, I walk you through the 4 grades of hydronephrosis, explain what’s happening at each stage, and show you when it’s time to take action. The good news? Most kidney stone sufferers will never get to the damage stage—because the body gives you warning signs before that happens.

Key Takeaways:

• Grade 1 and 2 hydronephrosis are common and rarely dangerous.

• Grade 3 introduces more consistent pain but still has low risk of damage.

• Grade 4 presents severe pain and a higher risk of kidney injury if untreated.

• Early recognition of symptoms and movement can often help resolve issues naturally.

When people first hear the word hydronephrosis, it sounds scary. And for good reason—it’s often associated with kidney damage and intense pain. But as someone who’s been through this myself and has helped countless others navigate it, I want to clear up some confusion around what this condition actually is, and how concerned you really need to be.

Let’s walk through the 4 grades of hydronephrosis so you can better understand what’s happening in your body, and when it’s time to take it seriously.

What Is Hydronephrosis?

Put simply, hydronephrosis is the swelling of the kidney due to a backup of urine. This backup usually happens because of a kidney stone blocking the flow. The more the urine gets backed up, the more your kidney starts to stretch—and that’s when we start seeing the different grades or levels of severity.

Let’s break them down. 

Grade 1: Mild Hydronephrosis

If your urologist tells you that you have mild hydronephrosis, you don’t need to panic.

This grade happens in almost every case where a kidney stone becomes symptomatic. That means the stone has moved into the ureter or the renal pelvis and is causing some kind of pain event that made you realize it’s there.

In this early stage, urine is just slightly backing up into the kidney’s internal collecting system. You probably won’t feel much of anything. No pain. No pressure. Just a minor internal change that’s usually visible only on an imaging scan.

Risk of kidney damage? Zero.

Grade 2: Mild-to-Moderate Hydronephrosis

Now we’re starting to see more noticeable changes.

In Grade 2, urine is backing up more significantly—especially into the renal pelvis, the part of the kidney that collects urine before it flows into the ureter.

You might start to feel a light pressure on the side of your body where the stone is located. It can come and go, but there’s still no pain at this point.

This stage is still considered mild. And the risk of kidney damage is still essentially zero. Your body is just managing the backup, and your kidney’s built-in defenses are doing their job.

Grade 3: Moderate Hydronephrosis

Now things are starting to get uncomfortable.

In Grade 3, urine starts backing up into the kidney’s collecting system itself—specifically into the medulla. This is the part of the kidney that contains the filtering structures and calluses.

As the medulla starts to thin out—losing up to 30–50% of its thickness—you’ll start to feel moderate pain. I usually rate it around a 5 out of 10. Enough to get your attention but not enough to drop you to the floor.

You’ll also start to feel more constant pressure, particularly in your mid-back where the kidneys sit. This is a sign that urine isn’t flowing properly and is creating internal expansion that your body doesn’t like.

Risk of damage? Still low, under 10%. But your body is signaling that something isn’t right.

Grade 4: Severe Hydronephrosis

This is where most people end up heading to the ER.

In Grade 4, the medulla is pretty much gone. It’s been pushed outward so much by the urine backup that the internal structure is completely overwhelmed.

Now the pressure moves to the cortex—the tough outer layer of the kidney. And that’s when the real pain starts.

I’m talking 9 out of 10 pain—the kind that feels like a nuclear explosion in your back. This is often the moment people realize they have a kidney stone and rush to the hospital.

At this point, your kidney is screaming for help. The cortex is less flexible than the internal areas and doesn’t handle pressure well. That’s why the pain becomes so sharp and unrelenting.

But here’s the important thing…

A Spike in Pain Doesn’t Always Mean Permanent Damage

You can move between these grades quickly.

It’s totally normal to go from Grade 1 to Grade 4 and then back again, depending on where your stone is and how well urine is flowing. Maybe the stone shifted, or maybe you weren’t drinking enough water. These things happen.

If you experience Grade 4 symptoms for less than six hours, you’re probably okay. But if that severe pain sticks around for more than six hours, it’s time to get help. And if it lasts more than 24 to 48 hours, the risk of permanent kidney damage increases significantly.

How to Help Your Body Clear the Blockage

There are a few things you can do if you’re stuck in a pain spike and want to avoid a hospital visit:

• Move around. Jumping, stomping, running—anything to physically shift the stone.

• Stay hydrated. Drink 2 to 3 liters of water daily to keep flow consistent.

• Watch for warning signs. Persistent pain, especially beyond 6 hours, is your signal to act.

Understanding Your Risk

Hydronephrosis isn’t a diagnosis—it’s a description of what your kidney is doing to protect itself.

Your kidney has multiple layers of defense. It starts with flexible areas like the renal pelvis, then works outward to the more rigid and sensitive structures like the cortex. And while it may sound scary, you’ll almost always feel warning signs before any real damage happens.

If your doctor says you have mild or moderate hydronephrosis, don’t panic. Pain—not imaging—is usually the best indicator of urgency.

Conclusion

So to recap the 4 grades of hydronephrosis:

• Grade 1: Minor backup. No pain. No damage.

• Grade 2: Renal pelvis expands. Slight pressure. Still no damage.

• Grade 3: Medulla thins. Moderate pain. Low risk of damage.

• Grade 4: Cortex stretches. Severe pain. High risk if prolonged.

Hydronephrosis sounds intimidating, but understanding what’s happening at each stage takes the fear out of the equation. I’ve been there. And knowing the difference between a temporary spike and true danger helped me make smarter decisions.