How to manage Mag3 (Mercaptoacetyltriglycine) renal scan uptake artifact in the stomach or gut?

MAG3 Renal Scan Uptake Artifact in Stomach or Gut

Understanding the Artifact

Gastric or bowel uptake of Tc-99m MAG3 is an uncommon but recognized artifact that typically indicates free pertechnetate contamination of the radiopharmaceutical, not true renal pathology. This occurs when the MAG3 preparation contains unbound technetium-99m, which is avidly taken up by gastric mucosa and can appear in the gastrointestinal tract 1.

Key Recognition Features

• Gastric uptake appears as focal activity in the stomach region that is distinct from renal parenchymal activity and does not follow the expected pattern of renal excretion into the collecting system 1
• The artifact typically manifests as persistent activity in the gastric fundus or bowel that does not wash out with the expected kinetics of urinary excretion 1
• This finding should not be confused with true renal pathology such as obstruction, acute tubular necrosis, or vascular complications 1

Immediate Management Steps

• Do not interpret the study as showing renal dysfunction based solely on apparent "uptake" in non-renal structures 1
• Verify radiopharmaceutical quality control data from the preparation to check for free pertechnetate contamination 1
• Consider repeating the study with a fresh MAG3 preparation if the clinical question remains unanswered, as this artifact renders the study non-diagnostic for renal function assessment 1

Differential Considerations

• Distinguish from urinoma: A true urinoma will show progressive accumulation of tracer in a perinephric collection that communicates with the collecting system, not gastric uptake 1
• Rule out patient factors: Ensure adequate hydration, as dehydration can cause abnormal tracer retention in renal parenchyma (though not gastric uptake) 2
• Gastric uptake is not related to renal obstruction, rejection, or vascular complications, which show characteristic patterns of delayed perfusion, reduced uptake, or impaired excretion within the kidneys themselves 1

Clinical Pitfalls to Avoid

• Do not proceed with clinical decisions based on a contaminated study - the presence of gastric/bowel activity invalidates the renal functional assessment 1
• Do not confuse this artifact with the normal bladder activity or ureteral visualization that should be present on MAG3 studies 1
• MAG3 is a tubular secretion agent with 40-50% extraction fraction, so any non-renal uptake pattern suggests technical issues rather than physiologic tracer handling 3

Recommended Action Algorithm

1. Immediately recognize the artifact by identifying uptake in gastric/bowel regions distinct from the urinary tract 1
2. Abort interpretation of renal function parameters from this study, as they will be unreliable 1, 3
3. Contact the nuclear medicine department to review quality control of the radiopharmaceutical preparation 1
4. Schedule repeat imaging with verified MAG3 preparation to obtain diagnostic information about renal function 1
5. If clinical urgency exists, consider alternative imaging such as ultrasound with Doppler for structural/vascular assessment or CT urography for anatomic evaluation 1, 4