Is there an onomatopoeia for coughing up blood?
"Is there an onomatopoeia for coughing up blood?"
No. There is no word that would resemble or simulate the sound of coughing up blood specifically. It wouldn't make sense to have one anymore than it would to have a sizzling sound or hissing sound specifically for the frying of a skirt steak versus chicken.
But, is there a word that resembles, simulates, or is associated with any sound that would resemble 'coughing up blood', like coughing up syrup, baby formula, or hot wax? Maybe something that starts with 'gla', or 'ghluh', but they kind of sound weird to me. Go with your gut on that one I guess.