Background:　Hyperglycemia　upon　admission　is　associated　with　poor　prognosis　of　many　cardiovascular　diseases.　However,　the　relationship　of　stress　hyperglycemia　ratio　(SHR),　admission　blood　glucose　(ABG),　and　hemoglobin　A1c　(HbA1c)　with　pulmonary　hypertension　has　not　been　reported.　This　study　aimed　to　explore　the　association　of　hyperglycemia　indices　with　disease　severity　and　long-term　adverse　outcomes　in　patients　with　idiopathic　pulmonary　arterial　hypertension　(IPAH).　Methods:　This　multi-center　cohort　study　included　625　consecutive　patients　diagnosed　with　or　treated　for　IPAH　between　January　2015　and　June　2023.　SHR　was　calculated　using　the　followings:　ABG　(mmol/L)/(1.59　×　HbA1c　[%]　−　2.59).　The　primary　endpoint　was　defined　as　clinical　worsening　events.　Multivariable　Cox　regression　and　restricted　cubic　spline　analyses　were　employed　to　evaluate　the　association　of　SHR,　ABG,　and　HbA1c　with　endpoint　events.　The　mediating　effect　of　pulmonary　hemodynamics　was　evaluated　to　investigate　the　potential　mechanism　between　hyperglycemia　and　clinical　outcomes.　Results:　During　a　mean　follow-up　period　of　3.8　years,　219　(35.0%)　patients　experienced　all-cause　death　or　clinical　worsening　events.　Hyperglycemia　indices　correlated　with　well-validated　variables　that　reflected　the　severity　of　IPAH,　such　as　the　World　Health　Organization　functional　class,　6-min　walk　distance,　and　N-terminal　pro-brain　natriuretic　peptide　levels.　Multivariable　Cox　regression　analyses　indicated　that　SHR　(hazard　ratio　[HR]　1.328,　95%　confidence　intervals　[CI]:　1.185,　1.489　per　0.1-unit　increment,　P　＜　0.001)　and　ABG　(HR　1.317,　95%　CI:　1.134,　1.529　per　1.0-unit　increment,　P　＜　0.001)　were　independent　predictors　of　primary　endpoint　events.　Mediation　analysis　indicated　that　pulmonary　vascular　resistance　mediated　5.65%　and　14.62%　of　the　associations　between　SHR　and　ABG　and　clinical　worsening　events,　respectively.　The　addition　of　SHR　significantly　improved　reclassification,　discrimination　ability,　and　model　fit　beyond　the　clinical　risk　prediction　model.　Conclusions:　SHR　is　positively　associated　with　clinical　worsening　in　patients　with　IPAH.　The　association　appeared　to　be　partially　mediated　through　the　pathway　of　pulmonary　vascular　remodeling,　indicating　that　SHR　may　serve　as　a　valuable　indicator　for　providing　additional　risk　information.　©　The　Author(s)　2024.