Besides hepatobiliary disease, Serum aspartate transaminase (AST) and alanine transaminase (ALT) also rise with skeletal & cardiac muscle injury (AST more than ALT) . To illustrate the clinical utility of this connection, we had discussed a case on this blog much before and I feel it will be useful to share how it helped me on three recent cases I worked with. (Patient details changed for HIPAA compliace )
Case 1: A middle aged lady with chronic leg lymphedema was admitted with leg cellulits and acute kidney injury with creatinine of 8 (baseline creatinine 1.5 ). Initial renal investigations were inconclusive but after noticing that her AST & ALT were up without good explanation, a CK level was checked, which was reported as 35,000 U/L ! No compartment syndrome – but she had forgotten to mention how she lay on the floor at home for few hours after a nasty fall at home few days prior.
Case 2: A guy in his 60s was admitted after an ankle fracture , which was surgically repaired and a leg cast was applied after. Had expected ongoing post-operative pain. Basic labs checked few days later showed a bump in AST & ALT . Since he had no signs/symptoms of hepatobiliary disease, a CK was checked and was reported as 5000 U/L. He was evolving edema & blisters under his leg cast from pressure/leg swelling, cast was removed and changed for risk of evolving compartment syndrome with a tight cast – and pain and CK levels improved !
Case 3: An elderly lady with coronary disease history underwent hip surgery after a fall which was uneventful. Next morning she was a little short of breath. Chest X-ray was clear. EKG showed no changes. She had no other complaints but labs showed a bump in AST levels without any clinical signs of liver of gallbladder idsease. So a CK & Troponin levels were checked – CK was normal but Troponin was very elevated. She ended up getting a angiogram & a coronary artery stent.
Interestingly, AST was the first biomarker ever used to identify acute myocardial infarction but abandoned since it isn’t specific to only cardiac tissue. That being said, knowing this can still be useful like in case illustrated above. A 2020 study out of China even found that AST/ ALT ratio of more than 2 can predict coronary artery occlusion in patients with Acute Myocardial Infarct. Conversely, if you see AST / AST rise in the setting of known muscle or cardiac injury, be careful iabout spending too much time, effort and money on chasing liver and gallbaldder disease which may not exist.
