Medically reviewed by Dr. Numair Younis, M.B.B.S. (K.E.M.U.), FEBNM European Fellowship in Nuclear Medicine, Consultant Nuclear Medicine Physician, Al-Nasar Lab & Diagnostic Centre. Updated September 2026.
Quick answer: A DTPA renal scan measures how well each kidney works on its own and whether urine is draining freely. A small amount of radiotracer is injected into a vein and a camera follows it through both kidneys. It takes about 30 to 45 minutes and answers two questions a blood test cannot: split function and obstruction.
Book a renal scan: call 0300 0341944. Nuclear medicine is performed at our main Johar Town campus.
Why is a blood test not enough?
This is the central point, and it explains why a urologist or nephrologist orders this scan at all.
A kidney function test measures creatinine and gives an eGFR. That is a single number describing both kidneys added together. It cannot tell you how the work is divided between them.
That distinction matters enormously. A person can have a perfectly normal creatinine while one kidney has quietly failed and the other has compensated by taking on the extra load. The blood test looks reassuring. The damage is real.
A DTPA scan reports the split, usually as a percentage such as 60 to 40 or 85 to 15. Before any decision to operate on, unblock or remove a kidney, that number is what the surgeon needs.
What does a DTPA scan show?
| Question | What the scan tells you |
|---|---|
| Split function | What percentage of the total work each kidney is doing |
| Obstruction | Whether urine is draining freely or held up, and at what level |
| Drainage pattern | Whether a widened collecting system is genuinely blocked or simply baggy |
| Overall filtration | A measured GFR rather than one estimated from creatinine |
| Transplant kidney | Blood supply and function of a transplanted kidney |
| Renovascular disease | Whether a narrowed renal artery is affecting function, sometimes with a captopril challenge |
DTPA or DMSA, which do you need?
These two are frequently confused because both are renal scans. They answer different questions.
DTPA is a dynamic scan. The tracer is filtered by the kidney and passes out into the urine, so the camera watches it flow through in real time. That movement is what reveals drainage and obstruction. It is the scan for blockage, drainage and split function.
DMSA is a static scan. That tracer binds to functioning kidney tissue and stays there. Images are taken a few hours later and show the working tissue itself. It is the scan for scarring, especially in children who have had repeated urine infections, and it gives the most accurate split function when scarring is the question.
In short: if the question is whether urine is getting out, DTPA. If the question is whether kidney tissue has been damaged, DMSA. Your specialist decides, and sometimes both are needed.
Who needs a DTPA scan?
- Suspected obstruction, most often at the junction where the kidney meets the ureter
- Hydronephrosis, meaning a swollen kidney seen on ultrasound, where the question is whether it is actually blocked
- Before kidney surgery, to know how much function that kidney still contributes
- Before removing a kidney, to confirm the other one can carry the load alone
- Recurrent kidney stones causing repeated blockage
- Transplant assessment, both for living donors and for monitoring a transplanted kidney
- High blood pressure suspected to come from a narrowed renal artery
- Children with antenatally detected hydronephrosis
Is the radiation safe?
This is the question almost every patient asks, and it deserves a straight answer.
The tracer dose used in a renal scan is small. The exposure is broadly comparable to other routine diagnostic imaging, and considerably less than several CT studies. The tracer is cleared by the kidneys themselves and largely passed out in urine within hours, which is why you are asked to drink plenty of water afterwards.
The material is not a contrast dye. Allergic reactions of the kind associated with iodinated CT contrast are not a feature of this scan, and it does not carry the kidney risk that contrast can in patients with poor renal function. That is one reason it is useful precisely in people whose kidneys are already impaired.
Tell the department if you are pregnant or breastfeeding. In pregnancy the scan is usually deferred, and if breastfeeding you may be asked to pause for a short period.
How to prepare
- Drink plenty of water before the appointment. Good hydration is essential, because a dehydrated kidney drains slowly and can mimic a blockage
- No fasting is required. Eat normally
- Take your usual medicines, but tell the department about blood pressure tablets, particularly ACE inhibitors, since these are paused for certain protocols
- You will be asked to empty your bladder immediately before the scan
- A cannula is placed in a vein, the tracer is injected, and you lie still under the camera while images are recorded
- A diuretic injection is often given partway through, which makes the kidneys produce urine quickly and shows whether drainage is truly obstructed. You will need to pass urine soon afterwards
- Allow around 30 to 45 minutes, sometimes longer if delayed images are needed
- Drink well and pass urine frequently afterwards to clear the tracer
- Bring previous ultrasound, CT and blood results, and your referral letter
Renal scanning at Al-Nasar Lab
Al-Nasar Lab & Diagnostic Centre has served Lahore since 1996 and holds ISO 15189:2022 accreditation from the Pakistan National Accreditation Council. Our nuclear medicine department operates under Pakistan Nuclear Regulatory Authority licensing and is staffed by a consultant nuclear medicine physician.
DTPA and DMSA renal scans are both available, alongside bone scans, thyroid studies and cardiac perfusion imaging. Because kidney assessment usually needs blood work alongside the scan, kidney function and electrolytes can be taken during the same visit.
See our renal scan service page, the wider nuclear medicine range, or contact us to book.
Frequently Asked Questions
How long does a DTPA renal scan take?
Usually 30 to 45 minutes, and longer if delayed images are required. Allow extra time for cannulation and preparation.
Do I need to fast for a renal scan?
No. Eat normally. What matters far more is arriving well hydrated, because dehydration slows drainage and can imitate a blockage.
What is the difference between DTPA and DMSA?
DTPA follows tracer moving through the kidney and answers questions about drainage, obstruction and split function. DMSA shows functioning kidney tissue itself and is the scan for scarring.
Is the radiation from a renal scan dangerous?
The dose is small and comparable to other routine diagnostic imaging. The tracer clears through the urine within hours, which is why drinking water afterwards is advised.
Can I have a renal scan if my kidney function is poor?
Yes, and it is often preferred in that situation, because it avoids the iodinated contrast used in CT that can further stress impaired kidneys.
This article is for general information and is not a substitute for medical advice. Please discuss your results with a qualified doctor.
