1. A system comprising: an implantable medical device including, an electrical impedance measurement circuit configured to measure one or more thoracic impedance-indicating signal characteristics, including at least a liquid 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, including values indicative of a liquid status, the memory circuit configured for storing a count representative of the one or more thoracic impedance-indicating signal characteristics, including at least the liquid status component, into a histogram bin having a numerically inclusive subrange; and a processor circuit including an input to receive and use information about the count representative of the one or more thoracic impedance-indicating signal characteristics, including at least the liquid status component, stored in the histogram to provide a lung edema status indication.