Is it an FHA loan or conventional? If FHA, you're required to carry mortgage insurance for 60 monthly premiums according to the major investors (freddy, fanny, gnma) regardless of your loan to value.
If conventional, you are usually eligible to have the mortgage insurance removed at 78%. Where I work, we figure loan to value by taking the lesser between the original appraisal value and the purchase price and divide the current principal balance against it. If your purchase price was greater than the appraisal value, we'll use the appraisal value from the original loan to determine loan to value.
For a conventional loan, if your LTV is too high but you feel that market conditions have improved, it doesn't matter. Structural improvements must be the sole reason for valuation increase in figuring a new LTV. Again this is a guideline set forth by fanny, freddy and gnma - not your mortgage company.
Another thing to consider is whether it is a primary or secondary home, as well if it's a 15 year or standard 30 year loan. Hopefully some of this helps.