Hematocrit is defined as the proportion of red blood cells in blood. For the proportion to increase in value without the numerator (# of RBCs) changing means only the denominator in the proportion can change (all other components in blood).
Given this concept, some symptoms that can cause increased hematocrit without change in number of RBCs:
-dehydration (loss of plasma volume)
-leukopenia (low amount of WBCs)