check up on vs pick up on

check up on

verb
  • To examine or inspect something in order to determine its condition; to check out. 

  • To look after or inquire about someone's well-being. 

pick up on

verb
  • To notice, observe, learn, or understand, especially something otherwise overlooked. 

  • To adopt a practice in which others already engage. 

  • To continue or build upon (for example, a task, analysis, or narrative), beginning from a point at which someone has previously stopped. 

How often have the words check up on and pick up on occurred in a corpus of books? (source: Google Ngram Viewer )