Copy number loss from ploidy 2 to either 1 or 0 results in LOH (Note that on a SNP-array, B Allele Frequencies look different for loss of 2 to 1 and loss of 2 to 0 ). However, it does not mean that when you see LOH, there is a copy number loss. For example, it can happen that the paternal allele is lost while the maternal allele is gained, resulting in LOH but no copy number alteration. This is called copy neutral LOH