text: user1771: In one scRNA-seq sample I encountered the genes: Hbb-bs, Hba-a1 and Hba-a2. These genes appear on top of the list of the highest expressed genes but the 75% percentile of cells have very low counts. Therefore the expression is highly skewed.
  
  Reading from gene cards, they appear to be coding hemoglobin subunits and involved in oxygen transport. I think they may need to be removed before normalization, also because the analysis I'm running does not consider oxygen transport.
  Has anyone encountered this situation and what do I do?
  
  user2388: You probably have red blood cell contamination.  It's probably better to identify which cells they are.  They'll probably cluster away from the cells you are interested in.
  
original_text: 1771: <p>In one scRNA-seq sample I encountered the genes: Hbb-bs, Hba-a1 and Hba-a2. These genes appear on top of the list of the highest expressed genes but the 75% percentile of cells have very low counts. Therefore the expression is highly skewed.</p>
  <p><a href="https://i.stack.imgur.com/D6ptW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/D6ptW.png" alt="enter image description here" /></a></p>
  <p>Reading from <a href="https://www.genecards.org/cgi-bin/carddisp.pl?gene=HBB&amp;keywords=hbb-bs" rel="nofollow noreferrer">gene cards</a>, they appear to be coding hemoglobin subunits and involved in oxygen transport. I think they may need to be removed before normalization, also because the analysis I'm running does not consider oxygen transport.</p>
  <p>Has anyone encountered this situation and what do I do?</p>
   2388: <p>You probably have red blood cell contamination.  It's probably better to identify which cells they are.  They'll probably cluster away from the cells you are interested in.</p>
  