What Size Of Kidney Stones Need Surgery? Experts Explain

From a grain of sand to a golf ball, kidney stones come in different sizes. Every size comes with certain complications. Smaller ones are usually not treated as a ‘threat’, because they pass on their own via urine. However, larger ones need more attention – as they generally require surgery. What is the exact size of kidney stones which require surgery? Today, we will explain all of this to you.

To get a better understanding of this, we reached out to experts, Dr Shashank MS, Consultant - Urology and Renal transplant, Aster CMI Hospital, Bangalore and Dr Pankaj Kumar Gupta, Urologist, CK Birla Hospitals, CMRI, Kolkata.

How Kidney Stone Size Determines Your Treatment Path

While small kidney stones are often not treated as a ‘threat’, one new study presents a different view. As per a 2022 study, published in the New England Journal of Medicine,leaving asymptomatic or small stones untreated may increase the risk of a patient's relapse in the following five years. “Kidney stone treatment depends mainly on the size of the stone and the symptoms it causes,” shares Dr Shashank. On this note, the expert shares in depth the surgery requirements for different sizes of kidney stones:

• Small stones (1-4 mm): For stones less than 2 mm, they usually pass on their own without surgery. These very small stones may cause mild pain or discomfort in the lower back or side, slight burning while passing urine, or no symptoms at all. Drinking plenty of water is usually enough to help them pass. For stones between 2–4 mm, most stones can still pass naturally, but they may cause more noticeable pain. Symptoms include sharp pain in the back or side, pain that comes in waves, nausea, and frequent urge to urinate. Surgery is usually not needed, but medical support may be required to manage pain and help passage.
• Medium stones (5-6 mm): For stones between 5–6 mm, the chances of passing naturally become lower. These stones often cause severe pain, vomiting, blood in urine, and difficulty in passing urine. Some people may still pass them with treatment, but in many cases, doctors may suggest procedures if the stone does not move or causes ongoing pain or infection.
• Larger than 7 mm: For stones larger than 7 mm, surgery or medical procedures are usually required. These stones are too large to pass on their own and can block the urinary tract. Symptoms include severe and constant pain, heavy blood in urine, repeated infections, fever, and reduced urine flow. Immediate medical care is important in such cases.

The following table comapres the varying features, symptoms and surgical needs of different size stones:

Shedding more light on this, Dr Gupta shares, “When stones are 4-10 mm, the likelihood of natural passage decreases. Symptoms become more pronounced, including severe flank pain (renal colic), nausea, vomiting, and blood in the urine. In such cases, if the stone does not pass or leads to infection or blockage, minimally invasive procedures like lithotripsy or ureteroscopy may be required. Stones larger than 10 mm rarely pass without medical intervention and typically require surgical removal. Patients often present with intense, persistent pain, recurrent urinary tract infections, and visible blood in urine. Advanced procedures such as percutaneous nephrolithotomy (PCNL) are commonly recommended.”

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Treatment Of Pregnant Patients With Kidney Stones

The American Urological Association shared certain treatment guidelines for pregnant patients with kidney stones:

• Imaging: When it comes to detecting kidney stones, ultrasound is the first choice. However, non-contrast MRI or CT are the backup options, if needed.
• Teamwork: All medications and surgical treatments that pregnant women undergo must be carefully coordinated with a medical professional.
• Waiting period: If the kidney stone symptoms are manageable, doctors generally suggest waiting to see if the stone passes on its own.
• Removal: If the stone does not pass naturally, then a procedure to physically remove it (ureteroscopy) may need to be performed.
• Alternatives: Another option for pregnant women is placing a drainage tube (stent or nephrostomy tube); but these need frequent replacing during pregnancy.

Does Kidney Stone Location Determine Surgical Need?

Did you know that not only the size, but the location of kidney stones can also influence the decision whether surgery is needed or not. The American Urological Association notes that for mid/distal ureteral stones (kidney stones lodged in the middle or lower tube leading to the bladder) under 10mm, observation and medical expulsive therapy (MET) should be given first. It further advised against Shockwave Lithotripsy (SWL) for lower pole stones larger than 10mm due to poor clearance rates; instead, it recommended Ureteroscopy (URS) or Percutaneous Nephrolithotomy (PCNL) for the same

A 2015 PubMed study, published in the Urology Annals, directly compares the treatment of stones in the lower pole versus the ones in other locations (such as upper pole, mid pole, ureter). The study cites that even when the stones are efficiently broken apart by shockwaves at the same rate, the stone-free rate (which indicates actually clearing the fragments from the body) is “statistically and significantly lower for lower pole stones”. The reason behind this is said to be the “anatomy impeding gravity-dependent drainage”.

When To Seek Medical Advice For Kidney Stones

Smaller kidney stones generally pass on their own, and can be treated using simple remedies at homes and medications. In this regard, mention must be made of the fact that certain stones are more prone to dissolution, and generally do not need surgery. As per the Institute of Urology, uric acid stones respond well to urine alkalinisation and oral citrate therapy. Similarly, cystine stones may be chemically modified and reduced with thiol-containing drugs. Struvite stones may also be limited through antibiotics and enzyme inhibitors. Calcium oxalate stones are the most common one (globally), which are said to be resistant to dissolution though medications or non-surgical remedies.

However, if the pain from stone becomes too severe and affects daily activities, and if you spot blood in your urine, then it is a clear indication that it is time to seek medical attention for your kidney stones. Explaining this further, Dr Gupta says, “In conclusion, while smaller stones can often be managed conservatively, larger stones particularly those above 10 mm generally require timely surgical treatment to avoid serious complications.”

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The Final Word

Kidney stones smaller than 4 mm usually pass naturally, but those between 5–10 mm may or may not need intervention. On the other hand, stones larger than 10 mm often require surgery, especially if symptoms are severe or complications develop.