Will a 4mm Kidney Stone Pass on Its Own?

Often, yes. A 4mm kidney stone is small, and Cleveland Clinic reports that around 90% of stones smaller than 6 mm pass out in the urine without a procedure. It can still be painful, and passing may take from one or two weeks to several weeks.

This guide is for adults who have been told about a small stone on a CT scan or ultrasound. It explains what the size usually means and which symptoms change the plan. It cannot tell you whether your own stone will pass; that depends on your scan, symptoms and clinical assessment.

Get urgent medical help the same day if you have kidney stone pain together with a high temperature, or you feel hot, cold or shivery. Healthdirect Australia advises going to an emergency department if you have stone pain (renal colic) with signs of infection such as fever. Infection behind a stone that is slowing urine flow is treated as an emergency, not something to wait out at home.

NIDDK and the NHS list other symptoms that need prompt assessment:

• Severe pain in the back, side, belly or groin, especially pain you cannot control.
• Fever or chills with any stone symptoms.
• Trouble passing urine, or passing only small amounts.
• Repeated vomiting so that you cannot keep fluids down.
• Visible blood in the urine, or painful urination.

CT is a common way to find stones because it shows their size, shape, number and position. A report might say a stone is 4 mm and give its location, for example inside the kidney or in the ureter, the tube that drains urine to the bladder.

Size is only part of the picture, so ask your team how the location affects their plan. NHS guidance notes that small stones are common, are unlikely to cause symptoms, and may pass without you noticing. Others cause cramping pain called renal colic, which can spread from the side or back to the groin and come and go.

The report may also mention swelling of the kidney, called hydronephrosis. This can happen when a stone slows the flow of urine. Our guide to mild hydronephrosis explains what that wording means and why it changes the follow-up plan.

Sources give slightly different timescales, and none can predict an individual stone. Cleveland Clinic says a stone smaller than 4 mm may pass within one to two weeks, so a stone measured at 4 mm sits at the edge of that group. The NHS says stones may take a few weeks to pass, and Healthdirect says it can take up to six weeks.

Cleveland Clinic advises following up with your healthcare provider if the stone has not passed within four to six weeks. Your own team may give a different review date based on your scan. Ask for the date in writing so you know when to call if nothing has changed.

The NHS says most stones are managed at home with fluids and pain relief, and that you will usually be advised to drink plenty of water. Follow the pain-relief plan your clinician gives you rather than combining medicines yourself. NIDDK notes that people who are vomiting and dehydrated may need hospital care for fluids given through a drip.

You may be asked to try to catch the stone when you pass it, so it can be sent to a laboratory. Knowing what the stone is made of can guide prevention advice. Your team will tell you how to collect it.

Larger stones, stones that block the urinary tract, or stones that cause great pain may need a procedure to break them up or remove them. Ask what would make your team move from waiting to treatment.

Stones can cause blood in the urine, either visible or found only on a dipstick test. Blood found on a dipstick still needs to be followed up as advised, because it can have other causes. Our guide to blood in urine on a dipstick explains why a repeat test is often arranged and what to ask about it.

Drinking enough fluid is the main step for most stone types. The NHS suggests adults drink 2.5 to 3 litres of water a day to prevent stones, and to check that urine is pale rather than dark. Some people need a different fluid target because of heart or kidney conditions, so check with your clinician first.

NIDDK and Cleveland Clinic describe other diet steps that may lower risk for some stone types:

• Eat less salt, including salt hidden in processed and fast foods.
• Limit large amounts of animal protein, while still eating enough protein overall.
• Do not cut out calcium from food. NIDDK explains that dietary calcium is not the cause of calcium stones and can help block stone-forming substances in the gut.
• If you have calcium oxalate stones, ask whether to limit high-oxalate foods such as spinach, rhubarb, nuts and wheat bran.
• Avoid drinking lots of fizzy, caffeinated or alcoholic drinks, as the NHS advises.

Bring the full scan report, not only a portal summary. These questions can help you leave with a clear plan.

• Where exactly is my stone: in the kidney or in the ureter?
• Does the scan show any swelling of the kidney or blockage?
• How long should I wait for the stone to pass, and when should I call if it has not?
• What symptoms mean I should go to an emergency department rather than wait?
• Should I collect the stone for analysis, and how?
• Will I need a follow-up scan to confirm the stone has gone?
• Do I need blood or urine tests to look for a cause, given my history?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a small stone described their scan wording, timelines and follow-up can help you notice questions you had not thought to ask. Similar cases cannot tell you what will happen with your stone, and they do not replace assessment by your own clinician. If you have fever or severe pain, seek care first.