Private Kidney Ultrasound London: Kidney Stones, Cysts, Infections and Flank Pain Explained

Your kidneys filter approximately 180 litres of blood every day, producing about 1.5 litres of urine and removing waste products, toxins, and excess fluid from your body. When something goes wrong — a kidney stone blocking urine flow, a cyst that needs characterisation, an infection that keeps coming back, or blood test results suggesting reduced kidney function — ultrasound is the first investigation your doctor reaches for.

A private kidney ultrasound provides a detailed, real-time assessment of both kidneys, the ureters, and the bladder in a single appointment. It can identify stones, cysts, obstruction, structural abnormalities, and signs of chronic kidney disease — all safely, painlessly, and without radiation.

At The Wellness London, every kidney ultrasound is performed by a GMC-registered doctor who interprets findings in real time, explains what they see during the scan, and provides a same-day written report. No waiting days for results. No uncertainty between the scan and a delayed phone call from your GP.

Need your kidneys checked? Message us on WhatsApp or email team@thewellnesslondon.com.

What a Kidney Ultrasound Examines

Both kidneys. Each kidney is measured and assessed for size (normal adult kidney is approximately 10–12cm in length), cortical thickness, echogenicity (brightness compared to the liver — increased echogenicity can indicate chronic kidney disease), and shape. The kidney parenchyma is examined for cysts, masses, and structural abnormalities.

Collecting system. The renal pelvis and calyces (the internal drainage system of the kidney) are assessed for dilation. Hydronephrosis — dilation of the collecting system — indicates obstruction, most commonly caused by a kidney stone blocking the ureter. Grading the severity of hydronephrosis (mild, moderate, severe) helps guide management urgency.

Kidney stones. Stones within the kidney appear as bright, echogenic foci that may cast acoustic shadows. Ultrasound can detect stones in the kidney itself and at the vesicoureteric junction (where the ureter enters the bladder). Stones within the mid-ureter can be more difficult to visualise on ultrasound due to overlying bowel gas.

Bladder. The urinary bladder is assessed for wall thickness, masses, diverticula, and stones. A post-void residual (PVR) measurement can be performed — you empty your bladder and the scan is repeated to measure the volume of urine remaining. Elevated PVR can indicate incomplete emptying, which is relevant for urinary symptoms, recurrent UTIs, and prostate-related obstruction in men.

Ureters. Normal ureters are not visible on ultrasound. If a ureter is dilated (visible), this indicates obstruction and raises the urgency of the investigation.

When Should You Get a Kidney Ultrasound?

Flank or loin pain. Pain in the side, between the lower ribs and the hip, is one of the most common reasons for kidney imaging. It may indicate kidney stones, infection, or other renal pathology. Renal colic — severe, colicky flank pain radiating to the groin — is classically caused by a kidney stone obstructing the ureter.

Blood in the urine (haematuria). Visible blood in the urine (macroscopic haematuria) or blood detected on a urine dipstick (microscopic haematuria) requires investigation. Ultrasound checks for structural causes including stones, masses, and bladder abnormalities. NICE guidelines recommend renal ultrasound as part of the haematuria investigation pathway.

Recurrent urinary tract infections (UTIs). Recurrent UTIs, particularly in men or women with frequent recurrence, may warrant imaging to check for structural abnormalities, stones, or incomplete bladder emptying.

Abnormal kidney function blood tests. Elevated creatinine, reduced eGFR, or abnormal electrolytes may prompt imaging to assess kidney size (small kidneys suggest chronic kidney disease) and exclude obstruction.

Known kidney cysts requiring monitoring. Patients with previously identified kidney cysts may need interval ultrasound to monitor stability.

Family history of polycystic kidney disease (PKD). Autosomal dominant PKD is the most common inherited kidney disease. Ultrasound screening can detect cysts in at-risk family members.

Suspected kidney obstruction. Any clinical scenario where urine outflow may be blocked — stone, tumour, enlarged prostate — requires ultrasound to assess for hydronephrosis.

Lower urinary tract symptoms. Difficulty passing urine, frequent urination, nocturia (waking at night to urinate), or a sense of incomplete emptying. A kidney and bladder ultrasound with post-void residual assessment is relevant.

Pre-operative assessment. Kidney ultrasound may be requested before urological procedures or as part of a general health assessment.

Screening and peace of mind. If you have risk factors for kidney disease (diabetes, hypertension, family history) and want a baseline assessment.

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Kidney Scans at The Wellness London: Pricing

All prices include the doctor-performed scan, verbal debrief, and same-day written report.

Kidney Stones: What Ultrasound Can and Cannot Tell You

Kidney stones affect approximately 1 in 10 people in the UK during their lifetime, and the incidence is increasing. They are more common in men, in people aged 30–60, and during warm weather (dehydration).

What ultrasound can do:

• Detect stones within the kidney (sensitivity varies by stone size — larger stones are more reliably detected)
• Identify hydronephrosis, which indicates a stone is causing obstruction — this is often the most clinically important finding
• Detect stones at the vesicoureteric junction (where the ureter enters the bladder)
• Assess kidney size and cortical health
• Evaluate bladder for stones

What ultrasound may miss:

• Small stones (under 5mm) can sometimes be difficult to visualise
• Stones within the mid-ureter are often obscured by overlying bowel gas
• Ultrasound cannot measure stone density (Hounsfield units) like CT can

When CT KUB may be needed: For confirmed or highly suspected acute renal colic, NICE guidelines recommend non-contrast CT KUB (CT of kidneys, ureters, and bladder) as the gold-standard investigation because it has higher sensitivity for all stone sizes and locations. However, ultrasound is appropriate as the first-line investigation in many clinical scenarios, particularly for patients with known stones, recurrent symptoms, pregnant patients, and those who want to avoid radiation.

Your doctor at The Wellness will advise whether ultrasound is sufficient for your clinical question or whether CT is recommended.

Kidney Cysts: When to Worry and When to Relax

Kidney cysts are among the most common incidental findings on abdominal ultrasound. Simple cysts are found in up to 50% of people over 50 and almost never cause problems.

Simple cysts are well-defined, thin-walled, fluid-filled structures with no internal features. They are benign and almost never require treatment or follow-up.

Complex cysts have features such as internal septations (walls within the cyst), calcifications, thickened walls, or solid components. These are classified using the Bosniak system:

• Bosniak I — simple cyst. Benign. No follow-up needed.
• Bosniak II — minimally complex. Benign. No follow-up needed.
• Bosniak IIF — mildly complex. Probably benign but requires follow-up imaging.
• Bosniak III — indeterminate. May be benign or malignant. Further evaluation needed.
• Bosniak IV — likely malignant. Surgical evaluation recommended.

Your doctor will characterise any cyst found on ultrasound and explain whether follow-up or further investigation is needed.

What to Expect During Your Kidney Ultrasound

Preparation: If the scan includes bladder assessment, drink approximately 500ml of water one hour before your appointment and avoid emptying your bladder. For kidneys-only assessment, no preparation is needed. If the scan is combined with an abdominal ultrasound, fasting for 6 hours may be requested.

The scan: You will lie on your back and may be asked to turn onto your side to optimise views of each kidney. The doctor applies gel and moves the probe across your abdomen and flank. The scan takes approximately 15–20 minutes for kidneys and urinary tract, longer if combined with other organs.

Post-void residual: If included, you will be asked to empty your bladder and return to the scanning bed for a quick measurement of the urine volume remaining. This takes under 5 minutes.

Results: Your doctor explains findings during the scan. A written report is issued the same day, typically within two hours.

Frequently Asked Questions

Is a kidney ultrasound painful? No. It is completely painless. You may feel mild pressure when the probe is pressed against your flank.

Can ultrasound detect kidney cancer? Ultrasound can identify renal masses. Small masses (under 3cm) may be difficult to characterise fully on ultrasound alone and may require CT or MRI for further assessment. However, many kidney cancers are first discovered incidentally on ultrasound.

Is one kidney scan enough? For a single clinical question (e.g., kidney stones, flank pain), one scan is usually sufficient. For monitoring known conditions, your doctor will recommend an appropriate follow-up interval.

Can I have a kidney ultrasound if I am pregnant? Yes. Ultrasound is safe in pregnancy and is the preferred imaging modality for pregnant patients with renal symptoms.

Book Your Kidney Ultrasound

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This article was reviewed by the clinical team at The Wellness London. All scans are performed by GMC-registered doctors. Last updated March 2026.

Medical disclaimer: This information is for educational purposes and does not replace professional medical advice. If you are experiencing severe flank pain with fever, visible blood in your urine, or inability to pass urine, please attend A&E or contact your GP urgently.