ICD-10 Kidney Stone

Here are the main types of kidney stones and their ICD-10 codes:

• Calcium oxalate stones (N20.0)
• Uric acid stones (N20.1)
• Cystine stones (N20.2)
• Struvite (infection-related) stones (N20.9)

Kidney stones, or nephrolithiasis, are small, hard deposits made of minerals and salts that form inside your kidneys. In 2026, we see more cases than ever due to changes in diet and hydration habits. For doctors and medical billers, getting the code right isn’t just about paperwork; it’s about ensuring the patient gets the right treatment plan and that insurance covers the necessary procedures.

When a patient walks into a clinic with sharp pain in their side (flank pain), the journey from diagnosis to coding begins. This guide breaks down everything you need to know about the ICD-10 N20 series.

The Main ICD-10 Codes for Kidney Stones

Coding for stones is all about location. You cannot simply use one code for every “stone” a patient has. The ICD-10-CM (Clinical Modification) system requires specific details.

1. N20.0 – Calculus of Kidney

This is the most common code used. It refers to stones that are physically located within the kidney itself. These are often called “renal stones.”

2. N20.1 – Calculus of Ureter

When a stone moves out of the kidney and gets stuck in the tube leading to the bladder (the ureter), the code changes. This is often when the most intense pain occurs.

3. N20.2 – Calculus of Kidney with Calculus of Ureter

If a patient is “unlucky” enough to have stones in both locations at the same time, you use this combined code. It is more efficient than listing N20.0 and N20.1 separately.

4. N20.9 – Urinary Calculus, Unspecified

This code is a “safety net,” but you should avoid it. It means a stone exists somewhere in the urinary tract, but the doctor hasn’t noted exactly where. In 2026, insurance companies often reject unspecified codes, so always try to be specific.

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Symptoms That Lead to a Diagnosis

To assign an ICD-10 code, the medical record must show a clear diagnosis. Doctors look for specific “red flags” during a physical exam:

• Severe Flank Pain: Pain that starts in the back and moves toward the groin.
• Hematuria: Blood in the urine (often looks pink or brown).
• Nausea: Many patients vomit because the pain is so intense.
• Dysuria: A burning feeling when peeing.

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Step-by-Step: How to Choose the Right Code

Accuracy in coding prevents “denied claims.” Follow this logic path when reviewing a patient’s chart:

Step A: Identify the Site

Look at the imaging report (like a CT scan or Ultrasound). Where is the stone?

• Kidney = N20.0
• Ureter = N20.1
• Bladder = N21.0

Step B: Check for Infection

Is there a fever or a positive urine culture? If the stone is causing a kidney infection (pyelonephritis), you may need to look at the N13.6 code for hydronephrosis with infection.

Step C: Look for Obstruction

A stone that blocks the flow of urine is more dangerous. If the stone causes the kidney to swell, this is called hydronephrosis. In this case, you use the N13 series of codes.

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Types of Kidney Stones and Their Impact

Not all stones are made of the same material. While the ICD-10 code usually focuses on location, the treatment depends on the type.

Stone Type	Common Cause	Coding Note
Calcium Oxalate	High salt/sugar diet	Most common type coded N20.0
Uric Acid	High protein diet or Gout	May require metabolic codes
Struvite	Chronic UTIs	Often associated with “Staghorn” stones
Cystine	Genetic disorders	Rare; requires specific genetic coding

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Diagnostic Procedures and ICD-10

Before a code is finalized, the patient undergoes testing. In 2026, the “gold standard” for diagnosis remains the Non-Contrast CT Scan.

1. Imaging: The radiologist identifies the size (in millimeters) and the location.
2. Urinalysis: Checks for blood and crystals.
3. Blood Tests: Checks calcium and uric acid levels to see why the stones are forming.

Proper documentation of these tests is what supports the use of N20 codes. If a doctor writes “suspected kidney stone” but the CT scan is clear, you cannot code N20.0; you must code for the symptoms instead (like R10.12 for left upper quadrant pain).

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Common Mistakes in Kidney Stone Coding

Even experienced billers make errors. Here are the top things to avoid:

• Using “Unspecified” too often: As mentioned, N20.9 is a red flag for auditors.
• Confusing Kidney Stones with Bladder Stones: Bladder stones use the N21 series, not N20.
• Forgetting Laterality: While the N20 code itself doesn’t always require a “left” or “right” modifier, the procedure codes (CPT codes) definitely do.
• Coding Symptoms Instead of the Diagnosis: Once a stone is confirmed, stop coding for the “pain.” Code the stone.

Treatment Options That Follow the Code

Once the N20 code is in the system, the treatment begins. The complexity of the code often dictates the treatment:

• Conservative Management: For small stones (under 5mm). The patient drinks water and waits for it to pass.
• Shock Wave Lithotripsy (SWL): Using sound waves to break the stone.
• Ureteroscopy: A small scope is used to remove the stone from the ureter (N20.1).
• PCNL: Surgery for very large stones (Staghorn calculi).

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Final Thoughts on Kidney Stone Documentation

To be successful in medical coding, you must be a detective. Read the doctor’s notes, look at the imaging, and ensure the location is clear. When you use the N20 series correctly, you ensure the healthcare system runs smoothly and the patient gets the care they deserve.

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