REF013 - Diuretic Renogram

The purpose of this document is to assist clinicians in deciding on the appropriateness of a Nuclear Medicine DTPA or MAG3 renogram for dynamic renal imaging and to give guidance on the mechanism of referral.

Renal Nuclear Medicine imaging provides both anatomical and functional information relating to the urinary tract. Both static and dynamic renal imaging can be performed. In many cases, both studies would be of use and the diagnostic question needs careful consideration. For example, in the investigation of reflux, static renal imaging is the investigation of choice for demonstrating renal scarring. Scarring may, however, be a residual effect of previous reflux. Dynamic renal imaging could be employed to demonstrate that reflux is continuing.

Dynamic renal images are most often obtained using technetium-99m labelled DTPA which is a true chelate and excreted by the kidney purely by glomerular filtration. Technetium-99m labelled MAG3 is an alternative to DTPA. Although MAG3 has a superior extraction efficiency than DTPA, it is more difficult to produce, and is significantly more expensive. MAG3 is therefore restricted to certain specific cases. These represent cases where it is particularly important to maximise renal uptake. For example, MAG3 should be used in all paediatric cases and in cases of renal failure or known poor renal function.

In contrast to static renal imaging, these radiopharmaceuticals are rapidly excreted and rapid sequential imaging must be performed. The images obtained provide information relating to renal vascularity, renal function and excretion.

An image obtained for the first 30 seconds of the study provides a “vascular image” with the major blood vessels and perfusion in both kidneys, liver and spleen being visualised. The amount of vascularity at each site reflects the relative vascularity. Renal function is assessed at 2 minutes post injection when there is good renal visualisation and an image will show the relative distribution of function between the kidneys. Thereafter, cortical activity rapidly diminishes as the radiopharmaceutical is excreted. Activity is normally seen in the collecting system by 5 minutes and serial images after this show progressive excretion of the radiopharmaceutical.

If a question of obstruction has not been resolved, images may be obtained following administration of the diuretic furosemide. An obstructed dilated upper urinary tract will be obstructed at low and high flow rates. A non-obstructed, dilated tract may appear obstructed at low flow rates due to stasis, but high flow rates, induced by a diuretic, will produce unimpeded washout from the upper tract.

In Paediatric patients, furosemide is usually administered approximately 15 minutes after administration of the radiopharmaceutical (F+15) and imaging continued to observe its effect. Furosemide should not be given if an indirect cystogram is to follow renogram imaging to look for reflux. If reflux is suspected but not seen on the conventional renogram, an indirect micturating study should be undertaken using the radioactivity present in the bladder. Following completion of the renogram, further dynamic images are acquired as the patient micturates with reflux appearing as spikes of activity returning up a ureter.

Furosemide is administered 15 minutes prior to the radiopharmaceutical, (F-15 renogram), routinely in adult renography to ensure a high flow rate during the whole investigation. If reflux is being investigated, as above, furosemide should not be given.

• The referrer may be any clinician holding a current valid medical qualification and currently employed in Secondary Care.
• Referrals from Primary Care will be accepted if the investigation has been suggested by a Consultant Radiologist in a report from a previous investigation, following discussion with a Consultant Radiologist, or recommended by a secondary care specialist. Details of such suggestions or discussions should be included on the request form.

Referring clinicians are reminded of the requirement to avoid unnecessary exposure to ionising radiation. The investigation may already have been requested at this hospital or elsewhere and clinicians are asked to be particularly vigilant to ensure that their request is not a double request.

Requests will only be accepted if the diagnostic question fulfills one of the referral criteria detailed in section 'Referral Criteria'. Appropriate clinical information must be supplied to allow the investigation to be justified. It is not acceptable to simply request the investigation without appropriate clinical information. Requests will be returned to the referrer if:

• The diagnostic question is unclear.
• The diagnostic question cannot be answered by the investigation.
• Insufficient clinical information is supplied to justify the investigation.

Requests should be submitted on the orange stripe NUCLEAR MEDICINE (ISOTOPE SCAN) request form. 'Patient details', 'Investigation required' and 'Reason for Test/Diagnostic Question' should be fully and appropriately completed and the form signed.

Renography on adults will routinely be performed with diuresis following the F-15 protocol. It should be clearly stated on the card if this protocol needs to be deviated from i.e. if the patient is allergic to furosemide, or if cystogram imaging is required.

For paediatric patients, if diuresis is required, this should be clearly stated on the request form. Furosemide will usually be given approximately 15 minutes after administration of the radiopharmaceutical. If a micturating study is required following the conventional renogram, then this should be clearly stated on the request form and furosemide will be withheld.

Dosage for Furosemide in adults with eGFR> 60 20mg. For eGFR<60, dosage is 40mg. Paediatric dosage is based on 0.5mg/kg up to a maximum of 20mg.

The referrer should indicate if this is NOT appropriate for their patient.

Sufficient clinical information must be provided to justify the investigation proceeding.

As stated earlier, there are many cases where both static and dynamic studies would be of use and the diagnostic question needs careful consideration.

All the clinical indications for a dynamic renal investigation using DTPA could equally be clinical indications for a dynamic renal investigation using MAG3. As explained in section 'Background' above, however, MAG3 is usually restricted to cases where it is particularly important to maximise renal uptake such as paediatric cases and cases of renal failure or known poor renal function (eGFR< 60).

The clinical indications are detailed below.

• The patient should be well hydrated at the time of administration of the radiopharmaceutical. They should be asked to drink 300 to 500ml of fluid on arrival in the department, proportionally less for paediatrics.