What indicates toxemia? bp high number, low number, or is it just a change from previous?

Many factors: Toxemia also known as preeclampsia is measured with elevation in blood pressure and protein in your urine. To qualify, you will need elevation in BP > 140/90 with a certain amount of protein in your urine. Furthermore, you may have additional symptoms associated with your elevated BP such as persistant headache, abnormal lung/liver function or platelet number that may qualify you for severe state.

BP + urine protein: Pre-eclampsia (sometimes called toxemia of pregnancy) is the combination of high blood pressure (hypertension), protein in the urine, and other symptoms during pregnancy. It happens when the blood vessels supplying the placenta are only able to accommodate the needs of the growing fetus by increasing the mother's blood pressure.

High blood pressure: Toxemia, also called preeclampsia, is diagnosed after 20 weeks gestation if your blood pressure is greater than 140/90 on 2 occasions 6 hours apart, and you have more than 300 mg of protein in your urine in a 24-hour urine sample.