Kidney Stone Diagnosis: Scans, Blood Tests and Urine Tests

Kidney stone diagnosis usually involves your medical history, an examination, and selected imaging and laboratory tests.

The aim is to establish whether a stone is present, where it is, and whether it is causing problems such as blocked urine flow. Symptoms alone cannot reliably identify what a stone is made of.

Seek urgent medical assessment for fever or chills, inability to urinate, uncontrolled pain, or persistent vomiting. Do not wait for a routine appointment when these symptoms occur.

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For optional reading alongside medical advice, view the Kidney Stone Removal Report. It is an information product and cannot confirm a diagnosis, identify a blockage, or replace medical testing.

What Do Kidney Stone Tests Check?

Different tests answer different questions. You may not need every test listed below.

Test or assessment	Main purpose
Medical history and examination	Assess symptoms, previous stones, medicines, and other possible explanations
CT scan	Identify stone size and location and assess urinary blockage
Ultrasound	Look for stones and swelling of the kidney without radiation
Abdominal X-ray	Identify or follow certain stones that are visible on X-ray
Urinalysis	Check for blood, crystals, and possible signs of infection
Urine culture	Identify bacteria when infection is suspected
Blood tests	Assess kidney function and selected mineral or infection-related markers
Stone analysis	Determine the composition of a collected or removed stone
24-hour urine collection	Investigate factors contributing to future stone formation

The immediate assessment and later prevention work-up have different purposes. Tests used to investigate recurrence do not replace imaging when a current obstruction is suspected.

What Happens at the First Assessment?

Your clinician will ask about the pain, associated symptoms, previous stones, medical conditions, and medicines or supplements you take.

Tell them whether you have noticed fever, vomiting, blood in the urine, or changes in urination. This information helps guide testing, but does not establish the diagnosis by itself.

Bring previous scan reports and stone-analysis results if available. Also mention pregnancy or possible pregnancy before imaging is arranged.

Our kidney stone symptoms guide explains common symptoms that may prompt assessment.

CT Scans for Kidney Stones

A non-contrast CT scan is commonly used to investigate suspected stones in adults. “Non-contrast” means the scan is performed without an injected contrast dye.

CT provides detailed images of the urinary tract and can help locate a stone and establish whether it is obstructing urine flow. It uses X-rays, so radiation exposure is part of the decision about which scan to choose.

A report may describe:

The stone’s size in millimeters.
Whether it is in the kidney or ureter.
Its position on the right or left side.
Whether more than one stone is present.
Evidence of urinary blockage.

Ask your clinician to explain the findings together. A measurement without its location does not provide the complete picture.

Ultrasound for Kidney Stones

Ultrasound uses sound waves rather than X-rays. It is generally the first imaging choice during pregnancy and for children.

It can show stones and dilation of the kidney’s collecting system. However, ultrasound can miss some stones, particularly those in the ureter. Further assessment may be needed when the findings do not explain the symptoms.

Follow the imaging department’s preparation instructions. For some kidney and bladder examinations, you may be asked to arrive with a full bladder.

What Does Hydronephrosis Mean?

Hydronephrosis describes dilation of the kidney’s urine-collecting system. It can be associated with obstructed drainage, but the finding needs interpretation in context.

The clinician must assess the cause and whether urgent action is needed. The term alone does not identify the stone’s composition.

Can an Ordinary X-Ray Detect a Stone?

Sometimes. An abdominal X-ray can show certain stones, but not all stone types are visible.

It may be useful for following a previously identified stone. A normal X-ray does not exclude every kidney or ureteral stone.

Your clinician will decide whether an X-ray provides enough information or whether another imaging method is needed.

Urine Tests: Blood, Crystals and Infection

Urinalysis

Urinalysis checks a urine sample for findings such as red blood cells, crystals, white blood cells, and bacteria.

These findings can support the assessment, but they need interpretation alongside symptoms and imaging. Crystals in a urine sample are not the same as laboratory analysis of an actual stone.

Urine Culture

When infection is suspected, a urine culture can help identify bacteria and guide antibiotic treatment.

Infection combined with an obstructed urinary system can require emergency drainage and antibiotics. Testing must not delay urgent treatment in a seriously unwell patient.

Do not assume that cloudy urine or burning automatically means either a stone or an infection. Report the symptoms so the cause can be assessed.

If you explore the Kidney Stone Removal Report, use it only as optional reading. Home observations cannot replace urine testing or imaging when infection or blockage is suspected.

What Do Blood Tests Show?

Blood tests help assess the wider effects of an episode and possible contributors to stone formation.

Depending on the situation, your clinician may check:

Creatinine: to help assess kidney function.
Electrolytes: including sodium and potassium.
Calcium: because an elevated level may require further investigation.
Uric acid: as part of the assessment of stone-forming risk.
Blood count and inflammatory markers: when assessing possible infection or inflammation.

Blood tests do not show the stone’s exact location or dimensions. They complement the scan findings rather than replacing them.

Ask which results need follow-up and whether they should be compared with previous measurements.

How Is the Stone’s Composition Identified?

Pain location, pain intensity, urine color, and the timing of symptoms cannot reliably distinguish calcium oxalate, uric acid, struvite, or cystine stones.

Laboratory analysis of a stone that has been passed or removed directly examines its composition. This helps guide prevention advice.

If your clinician recommends collecting a stone:

Use the urine strainer or collection method they provide.
Keep any recovered material in the recommended container.
Follow their instructions for storage and submission.
Ask when and how you will receive the result.

Some imaging techniques and laboratory findings provide clues about composition. However, these clues are not interchangeable with analysis of a retrieved stone, and stones may contain mixed materials.

Read our guide to the types of kidney stones for an explanation of the main categories.

When Is a 24-Hour Urine Test Used?

A 24-hour urine collection is generally part of a more detailed prevention assessment, particularly for people at higher risk of recurrence.

It measures what the kidneys release into urine over a full day. Depending on the clinical question, testing may include urine volume, calcium, oxalate, citrate, uric acid, sodium, and pH.

European Association of Urology guidance recommends two consecutive 24-hour collections for a specific metabolic evaluation. Your treating team will explain the protocol they use.

Follow the Collection Instructions Carefully

Ask the laboratory:

When to start and finish.
Which urine to discard at the beginning.
How to store the container.
Whether to continue your usual diet and medicines.
What to do if you miss a sample.

Tell the laboratory if the collection was incomplete rather than guessing the missing amount.

A prevention work-up is usually arranged once the acute episode has settled, under your clinician’s direction. For related information, see our recurrent kidney stone guide.

Questions to Ask About Your Results

Before leaving your appointment, ask:

Was a stone confirmed, or is the diagnosis still uncertain?
Where is it, and how large is it?
Is urine flow blocked?
Is there evidence of infection or impaired kidney function?
What treatment or observation plan do you recommend?
When should I have follow-up?
Do I need stone analysis or a prevention assessment?

Keep a copy of the report if possible. Our kidney stone treatment options guide explains the approaches your clinician may discuss after testing.

Frequently Asked Questions

Can a urine test alone confirm a kidney stone?

Usually, it cannot provide the complete answer. Urine findings may suggest a stone or another problem, but imaging is used to locate stones and assess obstruction.

Does every patient need a CT scan?

No. The choice depends on the circumstances. Ultrasound is especially important for children and during pregnancy, while non-contrast CT is commonly appropriate for suspected stones in adults.

Can a scan tell exactly what the stone is made of?

Sometimes imaging provides useful clues. However, a standard scan does not always establish the exact composition. A collected stone can be sent for laboratory analysis.

Are a routine urine sample and a 24-hour collection the same?

No. A routine sample examines urine collected at one time. A 24-hour collection measures urine output and substances excreted across a full day to help investigate stone-forming risk.

What if the scan does not explain my pain?

Ask what other causes need consideration and what to do if symptoms continue or worsen. Do not assume every episode of side or back pain is a stone because you have had one before.

Optional further reading: Kidney Stone Removal Report. Purchasing a report is not necessary to receive appropriate diagnostic testing, treatment, or prevention advice.

Resources

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Medical disclaimer: This article provides general information and does not replace personalized medical advice, diagnosis, or treatment. Symptoms and home observations cannot reliably establish stone composition or exclude urinary blockage.