TIPS Occlusion and Ammonia Levels
An occluded TIPS would be expected to decrease, not increase, ammonia levels because the occlusion restores hepatic first-pass metabolism by forcing portal blood back through the liver rather than bypassing it directly into systemic circulation. 1
Pathophysiologic Mechanism
The fundamental principle underlying this relationship is straightforward:
A patent (functioning) TIPS creates hyperammonemia by diverting ammonia-rich portal blood directly from the portal system into the systemic circulation, bypassing hepatic detoxification. 2, 3
Portal-systemic shunting decreases hepatic ammonia extraction, leading to elevated blood ammonia levels even in the absence of intrinsic liver disease. 2
When a TIPS occludes, portal blood is forced back through the liver, restoring hepatic ammonia metabolism and reducing systemic ammonia levels. 1
Clinical Evidence Supporting This Relationship
The 2025 EASL guidelines explicitly recommend therapeutic TIPS occlusion or reduction specifically to lower ammonia levels and treat refractory hepatic encephalopathy. 2, 1 This intervention would be counterproductive if occlusion increased ammonia.
Key supporting data:
Patients with lower baseline ammonia levels before TIPS placement paradoxically have higher risk of post-TIPS hepatic encephalopathy because they experience greater relative increases in ammonia after the shunt diverts blood away from the liver. 1, 4
TIPS reduction or complete occlusion is the definitive treatment for over-shunting complications, including severe recurrent hepatic encephalopathy (>3 episodes within 3 months) that results from chronic hyperammonemia. 2
Clinical Implications When TIPS Occludes
When evaluating a patient with suspected TIPS dysfunction:
Do not attribute new or worsening hepatic encephalopathy to TIPS occlusion—this represents a critical diagnostic pitfall. 1 The opposite pathophysiology applies: occlusion should improve encephalopathy by reducing ammonia burden.
If encephalopathy worsens with a patent TIPS, consider competing collaterals (spontaneous portosystemic shunts) that maintain excessive shunting despite the TIPS. 2 These require embolization before considering TIPS reduction.
Laboratory evaluation after TIPS occlusion should focus on portal hypertension complications (variceal bleeding, worsening ascites) rather than ammonia elevation, which would not be expected. 1
Diagnostic Approach to TIPS Dysfunction
Doppler ultrasound is first-line for detecting TIPS occlusion, with sensitivity and specificity of 0.96 and 1.0 respectively for complete occlusion. 2
Clinical symptoms suggesting TIPS occlusion include recurrent variceal bleeding or worsening ascites >3 months post-procedure, not hepatic encephalopathy. 2
Common Clinical Pitfall
The most important caveat: In patients with refractory hepatic encephalopathy and a functioning TIPS, always evaluate for large competing collaterals (spontaneous splenorenal shunts, gastric varices) before attributing symptoms to the TIPS itself. 2 These collaterals can maintain hyperammonemia even with appropriate TIPS function and require targeted embolization as first-line therapy before considering TIPS reduction or occlusion.