Kidney stones: the size decides, not the pain

The two numbers that should start every conversation

Ask two questions and write down the answers: how many millimetres wide is the stone, and where exactly is it. Everything else follows from these.

The best data on spontaneous passage comes from a study of nearly 400 ureteric stones measured carefully on CT. Within twenty weeks, stones of 0 to 3mm passed on their own 98% of the time. At 4mm, 81% passed. At 5mm, 65%. At 6mm, 33%. At 6.5mm and above, only 9%.

Location matters too. A stone in the lower ureter, close to the bladder, is more likely to pass than the same size stone higher up. A stone sitting quietly in the kidney itself may never cause a problem at all.

So a 3mm stone in the lower ureter in someone whose pain is controlled has an excellent chance of passing without any procedure. A 9mm stone in the upper ureter almost certainly will not. Being offered the same urgent procedure for both should prompt a question.

What pain does not tell you is size. Renal colic is caused by the ureter spasming against an obstruction and by pressure building behind it. A 3mm stone lodged at the narrowest point produces pain that people describe as worse than childbirth. The intensity of your pain is a reason for better pain relief; it is not evidence that you need surgery.

The one true emergency

Fever with a blocked kidney is the situation where nothing on this page about waiting applies. When urine cannot drain past a stone and that trapped urine becomes infected, the infection sits in a closed space under pressure and can progress to sepsis within hours. This is one of the genuine urological emergencies.

The signs are fever or chills together with loin pain, sometimes with shaking rigors, confusion, a rapid pulse, or feeling profoundly unwell. Guidelines are unambiguous: the obstructed system must be decompressed urgently, with a ureteric stent or a nephrostomy tube through the back, and antibiotics started. Attempting to remove the stone in that setting is dangerous, so decompression first and stone treatment later is correct practice, not delay or an extra charge.

Other situations that also need same-day attention rather than watchful waiting: complete absence of urine output, obstruction in a person with only one functioning kidney or a transplanted kidney, uncontrollable pain, persistent vomiting, and stone pain in pregnancy.

If you have loin pain and fever, do not spend time reading about stone sizes. Go to a hospital.

What observation actually involves

Observation is not being sent home to endure it. Done properly it means: a scan that has measured the stone and confirmed there is no dangerous obstruction and no infection, pain relief that genuinely works, plenty of fluid, sometimes a medicine to help passage, a defined review date, and a clear list of reasons to return immediately.

Guidelines support observation with or without medical expulsive therapy for uncomplicated distal ureteric stones of 10mm or less. An alpha blocker such as tamsulosin is commonly used to relax the lower ureter, and current guidance recommends it particularly for lower ureteric stones of 10mm or less. The evidence for benefit is modest and stronger for larger stones in the lower ureter than for small ones, so it is a reasonable adjunct rather than a cure.

For pain, non-steroidal anti-inflammatory drugs such as diclofenac are the mainstay for renal colic and generally work better than opioids for this specific pain. Ask what you should take, at what dose, and what to do if it is not controlling the pain.

There is a time limit. Most stones that are going to pass do so within four to six weeks. Guidelines caution against prolonged observation because sustained obstruction can damage the kidney silently. So observation should come with a review date and a repeat scan, not an open-ended instruction to drink water and hope. If the stone has not moved after that period, treatment is the reasonable next step and agreeing to it is not a defeat.

Straining your urine to catch the stone sounds trivial and is genuinely useful. If you catch it, the stone can be analysed, and knowing its composition changes your prevention plan substantially.

The procedures, and what each one is actually for

Shockwave lithotripsy, often called ESWL, uses focused shockwaves from outside the body to break the stone into fragments you then pass. It requires no incision and often no general anaesthesia. It suits smaller stones in favourable positions, works less well on very hard stones and in people with a high body mass index, and may need more than one session. Ask how many sessions are included in the price and what happens if fragments do not clear.

Ureteroscopy with laser, sometimes called RIRS when performed inside the kidney, passes a fine scope up through the bladder and ureter and breaks the stone with a laser. Stone-free rates are high and it works for stones that shockwave cannot manage. It usually requires anaesthesia and very often leaves a ureteric stent in place afterwards.

Percutaneous nephrolithotomy, PCNL, creates a small track through the back directly into the kidney. It is the appropriate treatment for large kidney stones, generally above about 2cm, and for stones filling the collecting system. It is the most invasive of the three, with a longer recovery and a higher complication rate, and it is also the right answer for stones the others cannot clear.

Open stone surgery is now uncommon and reserved for unusual anatomy or very complex stone burdens. If open surgery is proposed, ask why endoscopic options are not suitable in your case.

The honest position is that the choice between these is genuinely technical and depends on stone size, hardness, position, your anatomy, your body weight and what equipment and expertise are available. A good discussion names your stone size, explains which options fit it, and gives you the stone-free rate and the chance of needing a second procedure for each.

The stent nobody warns you about

A ureteric stent is a soft tube left between the kidney and the bladder to keep urine draining. It is placed for good reasons: after ureteroscopy, to relieve an obstructed kidney, or to allow an inflamed ureter to settle. It is also the single most common source of complaint after stone treatment, because patients are frequently not warned what having one feels like.

With a stent in place, it is common to have a frequent and urgent need to pass urine, blood in the urine, a dragging pain in the loin when you pass urine, and discomfort on movement. This is expected, not a complication. Knowing it in advance turns a frightening week into an uncomfortable one.

What matters far more is that stents must be removed or changed. A stent left in place for months can become encrusted with stone material, block, and cause serious kidney damage, and removing a long-forgotten encrusted stent is a difficult operation in itself. Before you leave hospital, get the removal date in writing, get it in your own note as well as the file, and confirm who is responsible for arranging it.

Ask also whether the stent has a string left attached, since some are designed to be removed without a scope, and whether removal is included in the price you have already paid.

Preventing the next one, which is the part usually skipped

Roughly half of people who form one stone form another within about ten years, and prevention is the cheapest urology available. It is also the part most often left out of a discharge summary.

Fluid is the foundation. The target is enough water spread through the day to keep urine pale, which in Indian summers and for anyone doing outdoor or physical work means considerably more than they think. Dehydration from heat and sweating is a major driver of stone formation in much of India.

Diet advice is frequently given wrongly. For the commonest stone type, calcium oxalate, cutting dietary calcium is counterproductive: normal dietary calcium binds oxalate in the gut and reduces stone formation, whereas a low-calcium diet increases risk. What does help is reducing salt, moderating animal protein, limiting very high-oxalate foods if you are a known oxalate former, and adding citrate, which is why lemon juice in water is a genuinely useful and very cheap intervention.

If you have had more than one stone, formed a stone young, have a family history, have only one kidney, or your stone was an unusual type, ask for a metabolic assessment: blood tests, a 24-hour urine collection, and stone composition analysis if the stone was retrieved. Uric acid stones in particular can sometimes be dissolved with medication that alkalinises the urine, which is a real non-surgical option that gets missed when nobody has established the stone type.

Ask directly at discharge: what type was my stone, what should I change, and do I need any tests to find out why this happened? A discharge with no prevention plan means you will probably meet the same hospital again.