Kidney Stone Test: Which Tests Diagnose Stones? Complete Guide
- When do you need a kidney stone test?
- Imaging tests: CT, Ultrasound, KUB X‑ray (comparison table)
- Urine tests: Dipstick, microscopy, 24‑hour collection
- Blood tests: Creatinine, calcium, uric acid
- Stone analysis: Why you must save the stone
- Which test is best for you? (Decision guide)
- Interactive FAQ – 9 common questions
When do you need a kidney stone test?
Not every flank pain requires imaging. Indications for diagnostic testing include:
- Severe, colicky flank pain suspicious for renal colic.
- Visible blood in urine (gross hematuria) with pain.
- Known history of stones with new symptoms.
- Fever with flank pain (rule out obstructive pyelonephritis).
- Follow‑up of known stones to assess size, location, or hydronephrosis.
At Vivekananda Hospital, we use a step‑wise approach starting with ultrasound (no radiation) and progressing to CT if needed.
Imaging tests: CT, Ultrasound, KUB X‑ray (comparison table)
These are the primary imaging modalities for diagnosing kidney stones.
| Test | What it shows | Accuracy | Radiation | Cost (India) | Best for |
|---|---|---|---|---|---|
| Non‑contrast CT (NCCT) KUB | Stone size, location, density (HU), hydronephrosis, alternative diagnoses | >98% (gold standard) | Yes (2‑5 mSv) | ₹3,000‑5,000 | Emergency, complex stones, surgical planning |
| Ultrasound (USG) KUB | Hydronephrosis, large stones (>3mm), bladder stones | 60‑80% (misses small stones) | None | ₹800‑1,500 | Pregnancy, children, follow‑up, screening |
| KUB X‑ray (plain abdomen) | Radio‑opaque stones (calcium, struvite) | 50‑60% (misses uric acid, small stones) | Low (0.7 mSv) | ₹300‑600 | Tracking stone position after ESWL, cheap screening |
Urine tests: Dipstick, microscopy, 24‑hour collection
Urine tests serve two purposes: diagnosing stone complications and identifying metabolic risk factors for recurrence.
Urinalysis (dipstick and microscopy)
What it detects: Red blood cells (hematuria), white blood cells (infection), nitrites, pH, crystals.
When to do: All patients with suspected stones. A negative dipstick does not rule out stones (some stones do not cause visible blood).
Cost: ₹100‑200.
24‑hour urine collection (metabolic evaluation)
What it measures: Volume, calcium, oxalate, uric acid, citrate, sodium, creatinine, pH, magnesium, phosphorus.
When to do: After stone passage or removal, for recurrent stone formers (≥2 stones in lifetime) or high‑risk patients (solitary kidney, family history, children).
Cost: ₹2,000‑3,500.
Interpretation: Identifies hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria – each has specific prevention strategies.
Blood tests: Creatinine, calcium, uric acid
Blood tests assess kidney function and identify systemic abnormalities.
- Serum creatinine & eGFR: Baseline kidney function. Elevated creatinine suggests obstruction or pre‑existing CKD.
- Serum calcium (corrected for albumin): High calcium may indicate hyperparathyroidism, a cause of recurrent stones.
- Uric acid: High levels suggest uric acid stones or gout.
- Electrolytes (sodium, potassium, chloride): Rule out renal tubular acidosis (RTA) – a cause of hypocitraturia.
Cost: ₹500‑1,000 for basic metabolic panel.
Stone analysis: Why you must save the stone
If you pass a stone or have one removed surgically, you must send it for laboratory analysis (infrared spectroscopy or X‑ray diffraction). This tells you the exact stone composition: calcium oxalate (monohydrate vs dihydrate), calcium phosphate, uric acid, cystine, or struvite.
Why it matters: Prevention is stone‑specific. For calcium oxalate stones, you reduce oxalate and maintain calcium. For uric acid stones, you alkalinise urine and reduce purines. For cystine, you need specific medications. Without analysis, you are guessing.
Cost: ₹500‑1,000.
Which test is best for you? (Decision guide)
Based on your clinical scenario, here is the recommended first test at Vivekananda Hospital:
- Acute severe flank pain (suspected stone): Non‑contrast CT (fastest, most accurate).
- Pregnancy or child with flank pain: Ultrasound first. If negative but high suspicion, MRI without contrast (no radiation).
- Known stone on follow‑up: Ultrasound to check for hydronephrosis and stone growth.
- After ESWL or URS: KUB X‑ray or ultrasound to confirm stone‑free status.
- Recurrent stone former (≥2 stones): 24‑hour urine + stone analysis + blood work.
- First‑time stone former with risk factors (family history, solitary kidney, young age): Same as recurrent – metabolic evaluation.
Interactive FAQ – Kidney stone tests
Very rarely. Non‑contrast CT detects stones as small as 1mm with >98% sensitivity. Missed stones are usually very small (<1mm) or uric acid stones if thin‑slice protocol not used.
Ultrasound is good for hydronephrosis and stones >3mm in the kidney or bladder, but misses many ureteral stones. If ultrasound is negative but symptoms persist, CT is needed.
About 2‑5 mSv, equivalent to 1‑2 years of natural background radiation. Modern low‑dose protocols use <2 mSv. The risk is small but not zero; only do CT when clinically indicated.
You collect all urine over 24 hours in a special container (avoid the first morning void of day 1, then collect every drop including first void of day 2). Keep refrigerated. Bring to lab.
1‑3 days. The lab uses infrared spectroscopy to identify crystal composition.
Indirectly. High uric acid suggests uric acid stones. High calcium suggests hyperparathyroidism. But definitive stone type requires stone analysis.
Only if you had hydronephrosis or multiple stones. If you passed the stone and symptoms resolved, a repeat ultrasound or KUB X‑ray is sufficient to confirm no residual obstruction.
No. Non‑contrast CT is the standard. Contrast is only added if a stone is not found and you suspect other pathology (tumour, infection).
After starting preventive therapy, repeat at 3‑6 months to check response. Then annually if stable.
Disclaimer: Choosing the right test depends on your symptoms, risk factors, and pregnancy status. Always consult a urologist at Vivekananda Hospital for personalised diagnostic guidance.