[Geotiff] USGS Geotiff parameters

[Church, Brian J]

Hello, I am new to the Geotiff format and raster image processing in general.   My question concerns the Geotiff files from the NED downloaded via the seamless.usgs.gov website.  Is it possible to extract elevation data from these files?  From what I understand, the 3rd value in the PixelScale tag provides the scale for the elevation data.  Is that correct?  However, this value is zero for the few files I have downloaded.   Also, I understand the TiePoints tag would provide the base elevation.  But again, there is only the x,y values. 
 
Note: I do not have Arc at my disposal.  I am using Matlab to read these files.  
 
Any info is greatly appreciated.
 
Thanks in advance,
Brian Church