The ESR represents a nonspecific response to tissue damage and inflammation and denotes the presence of disease, but not its severity.  It primarily reflects changes in the plasma proteins that accompany most the acute and chronic infections, tumors, and degenerative diseases.  It may be used to follow the progress of certain diseases such as tuberculosis and rheumatoid arthritis.                                                                                   The sedimentation of red blood cells takes place in three stages:                 In the first 10 minutes (lag phase) rouleaux formation occurs and the sedimentation rate is slight.

  Sedimentation then occurs for a period of approximately 40 minutes at a more rapid and constant rate.

During the last 10 minutes, the sedimentation rate is slow because of the accumulation of RBCs in bottom of the tube.  The longer the tube the longer the stage two will last, and therefore the higher the ESR result..........