A decline in price along with an increase in OI shows short build-up.

Source: https://www.thehindubusinessline.com/portfolio/commodity-analysis/fo-tracker-derivatives-traders-positioning-bearish/article67212494.ece

Derivative traders seemed very active as the Open Interest (OI) on futures saw substantial increase mid-week.

Source: https://www.thehindubusinessline.com/portfolio/commodity-analysis/fo-tracker-derivative-participants-remain-bearish/article66552009.ece

Furthermore, the drug's use may be limited to no more than 12 consecutive months, which may complicate treatment given the complexity and variability of OI.

Source: https://seekingalpha.com/article/4580535-ultragenyx-and-mereo-setrusumab-for-osteogenesis-imperfecta-criticisms-and-concerns?source=feed_all_articles

OI is colloquially known as "brittle bone disease".

Source: https://seekingalpha.com/article/4577189-ultragenyx-rating-speculative-buy-playing-setrusumab-data-release?source=feed_all_articles

The OI increased to 25.3 lakh contracts on September 22 as against 20.5 lakh contracts on September 15. So, there was a considerable short build-up.

Source: https://www.thehindubusinessline.com/portfolio/commodity-analysis/fo-tracker-bears-knocking-the-door/article67337263.ece