Labelled red-cell scintigraphy — dynamic abdominal acquisition
Anterior abdomen and pelvis in a single field of view, acquired dynamically for at least 60-90 minutes, with delayed images at intervals up to 24 hours where bleeding recurs.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Obscure or intermittent gastrointestinal bleeding where CT angiography has been negative and the patient continues to bleed.
- Clinically significant bleeding at a rate too low for CT angiography to demonstrate — the labelled pool detects slower bleeding than an arterial-phase CT can resolve.
- Localisation of a bleeding territory before catheter angiography or surgery, to shorten and direct the subsequent procedure.
- A patient in whom iodinated contrast is contraindicated and localisation is still required.
Technique
- In-vitro labelling of the patient's own red cells gives the most stable label; in-vivo and modified in-vivo methods are quicker but leave more free pertechnetate.
- The diagnostic finding is an intraluminal focus that appears where there was none, increases in intensity, and moves antegrade or retrograde in the bowel on the cine review — a static image cannot make the diagnosis.
- The dynamic acquisition is reviewed as a cine; this is the single most important part of the technique and is where the study differs from a series of delayed static images.
- Because the label persists for hours, the patient can be reimaged when bleeding recurs, which is exactly the advantage in intermittent bleeding.
Where it goes wrong
- Localisation is territorial, not lesional: bowel is mobile and activity migrates, so a focus reported as "right colon" can be small-bowel in origin, and delayed static images without the intervening cine are the classic cause of mislocalisation.
- Free pertechnetate from a poor label accumulates in gastric mucosa, thyroid and urine and is repeatedly mistaken for bleeding.
- A negative study means only that the patient was not bleeding fast enough during the acquisition — it does not exclude a bleeding lesion, and the pathway should continue.
- It is a localising test, not a therapeutic one; the definitive result is the catheter angiogram, endoscopy or resection it directs, and it should not be requested where the patient needs immediate haemostasis.
- Not the right test in massive haemorrhage: an unstable patient needs CT angiography and interventional radiology, not a 90-minute acquisition.
Clinical questions that reach this study
Contrast
None
Acquisition
- Preparation
- In-vitro labelling gives the best label stability; state locally which method is used, because free pertechnetate changes how gastric and urinary activity are interpreted. The patient must be able to lie still for a dynamic acquisition of at least 60-90 minutes, and be accessible for delayed imaging afterwards.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Intravenous access adequate for the planned injection· radiographer at scan
- Pregnancy status before an ionising exposure· radiographer at scan