My daughter's GI and rheumatologist told us that ESR is not a good indicator - both pediatric and adult GI did not usually order ESR. They preferred CRP. In her case, we definitely have to do labs because she has arthritis and unfortunately there is no marker like Fecal Calprotectin that shows inflammation specifically in the joints. So CRP is as good as it gets.
My daughter used to always have normal blood work - both CRP and ESR were thoroughly normal even when she had very obviously inflamed joints or an elevated FCP. But when she was around 18 years old it changed and her CRP is now always high. It only ever becomes normal when she's on steroids, so her doctors are sure it's inflammation that's making it high. So they just look at the trend for her. Her ESR is sometimes high, not always.
Same with her FCP - hers tends to be low. The highest it's been is roughly 480. So her GI watches the trend - when she's doing really well, it's under 50. When she was in remission this summer, it was 15! But she recently flared (both joints and gut) and while CRP and ESR were high - CRP was 19 (range 0-3), ESR was 66 (range 0-20) but FCP was only 140, even though she had blood in her stools.
She has CRP and FCP done every 3 months typically. If she's flaring, her rheumatologist sometimes does CRP more often. In her case, platelets are also always high due to inflammation.