In English, there are two related phrases that I haven't found an idiomatic Spanish translation for: "to check in (on someone)" and "to follow up (with someone)."
Some examples of what I mean:
I send someone an email and don't hear back for several days. In the second email, I might say something like "I'm just checking in to see what you thought about (whatever I asked in the first email)" or "I just wanted to follow up on the email I sent last week."
A friend is sick and we haven't talked for a few days, so I call and say, "I just wanted to check in on how you are doing." He might then call the doctor and say, "I'm following up to see if the test results are in."
These might all be slightly different concepts, but they all seem related to the idea of talking to someone a second time, referencing a conversation/correspondence in the past.
Is there a word or phrase in Spanish that has the same range of meaning as these English phrases? If not, what would be the most natural way in Spanish to express the sentences in the examples above?