CHI3L1 and hypersensitivity pneumonitis: On the other hand, even though biomarkers such as KL-6, SP-D, YKL-40 and apolipoproteins have not made their way to the day-to-day diagnostic approach to fibrotic HP in most tertiary centers, they have shown, in our opinion, promising results on research contexts and have the potential to translate into clinical practice once reproducibility is further confirmed.