1. A system comprising: an implantable medical device including: an electrical impedance measurement circuit configured to measure at least one thoracic impedance-indicating signal characteristic, including at least a fluid status component, using information about electrical energy injected between two or more electrodes and a potential difference created thereby between the same or different two or more electrodes; and a memory circuit including a number of histogram bins, each bin representing a subrange of thoracic impedance-indicating signal characteristic values, the memory circuit configured for storing the at least one thoracic impedance-indicating signal characteristic into a histogram bin having a numerically inclusive subrange; and a processor circuit including an input to receive and use information about the at least one thoracic impedance-indicating signal characteristic stored in the histogram to provide a lung fluid status indication.