This paper provides a state-of-art review on healthcare-IoT infrastructure, prominently focusing on protocol standards, enabling technologies, wireless body area network (WBAN) architectures and implementation issues. Internet of Things enchains the seamless healthcare devices from an actuate-sense-communicate (ASC) network in a proliferative channel in order to develop an operationally connected healthcare environment (OCHE). Sensors and actuators are the essential components of any IoT system that generates enormous data, and this data is communicated across the network concerning elementary statuses and stored in a distributed cloud platform. This paper begins by providing a brief horizontal overview of the IoT system. The enhanced technical details pertaining to healthcare scenarios such as WBAN architecture, layered healthcare IoT architecture, and enabling technologies are described in the forthcoming fragments of the paper. Authors have then provided a brief summary of the most anticipated protocol stacks and design issues that allows researchers and healthcare professionals to understand swiftly how the numerous protocols put together to attain desired functionalities without having to get through standards and RFCs. Authors have also explored recent state-of-art to identify some of the key challenges of the healthcare IoT domain and a short summary of each related research is presented. Moreover, the relation between Healthcare IoT and other disruptive technologies such as Blockchain and Big Data is being described. Finally, the authors explicated the detailed use-case scenarios to demonstrate how the numerous protocols and architectures presented in the paper could put together to attain desired healthcare services.