GDF15 and tuberculosis: In addition, serum GDF15 levels also had a strong positive correlation with TB (r = 0.6232, p < 0.0001), AST (r = 0.5205, p < 0.0001), PT-INR (r = 0.6332, p < 0.0001), and the Fib 4 index (r = 0.6717, p < 0.0001).