"Patients with an abnormally low systolic-diastolic ratio may need to be evaluated for internal bleeding." etc. There is very little here about the actual ratio, which would be the figure from dividing the systolic by the diastolic, often about 1.6 .
Does that sentence really refer to the ratio, or to the two figures? For example, 80/50 would be a low blood pressure, but the ratio would be quite normal at 1.6.