Final answer:
The percentage of plasma in a patient's blood can be calculated by subtracting the hematocrit value from 100.
Step-by-step explanation:
The percentage of plasma in a patient's blood can be calculated by subtracting the hematocrit value from 100. For example, if the hematocrit is 42 percent, then the percentage of plasma would be 100 minus 42, which is 58 percent.