Macro that looks for different values in cells - having trouble with zero and blank

I have a macro that looks up or down from the currently selected cell and looks for when the cell contents change, e.g. suppose you have a hundred entries of "dog" in a column and this changes at some point to "cat", the macro selects the cell at the change-over point by iterating through the cells and looking for when the cell value changes.

However it doesn't know the difference between a blank cell and a cell with a zero in it (both equal zero according to VBA). I have a kind-of solution using WorksheetFunction approach (using Count or CountA) but it takes aaaages to run, presumably since it's using a worksheet function.

Can anyone think of a more efficient way to check the contents of two cells? I need a quick way to compare the contents and flag up if one is blank and one contains a zero.

Cheers!
Rob

If IsEmpty(ActiveCell.Value) Then
Do one thing
'else is optional
Else
Do something else
End If

Would that work for your blank cells?