Purpose: Create an index of global reach for healthcare hashtags and tweeters therein, filterable by topic of interest. Materials and methods: For this proof-of-concept study we focused on the field of Primary Care and Family Medicine. Six hashtags were selected based on their importance, from the ones included in the `Healthcare Hashtag Project'. Hashtag Global Reach (HGR) was calculated using the additive aggregation of five weighted, normalized indicator variables: number of impressions, tweets, tweeters, user locations, and user languages. Data were obtained for the last quarter of 2014 and first quarter of 2015 using Symplur Signals. Topic-specific HGR were calculated for the top 10 terms and for sets of quotes mapped after a thematic analysis. Individual Global Reach, IGR, was calculated across hashtags as additive indexes of three indicators: replies, retweets and mentions. Results: Using the HGR score we were able to rank six selected hashtags and observe their performance throughout the study period. We found that \#PrimaryCare and \#FMRevolution had the highest HGR score in both quarters; interestingly, \#FMChangeMakers experienced a marked increase in its global visibility during the study period. ``Health Policy{''} was the commonest theme, while ``Care{''}, ``Family{''} and ``Health{''} were the most common terms. Discussion: This is the first study describing an altmetric hashtag index. Assuming analytical soundness, the Index might prove generalizable to other healthcare hashtags. If released as a real-time business intelligence tool with customizable settings, it could aid publishing and strategic decisions by netizens, organizations, and analysts. IGR could also serve to augment academic evaluation and professional development. Conclusion: Our study demonstrates the feasibility of using an index on the global reach of healthcare hashtags and tweeters. (C) 2016 Elsevier Inc. All rights reserved.