Keeping score and calculating relative size is key to surveillance and surgical timings. The Z-score is a formula used to monitor the aorta, particularly during the childhood growth years. What is it?
The guidelines for management of aortic disease in adults routinely use absolute aortic diameters to guide surveillance and surgical timings for people with Marfan syndrome and Loeys-Dietz (MFS/LDS). The aortic size is reported in centimetres (cm). Depending on the specific genetic change or other factors like family history, the aortic size will be monitored to ensure that any required surgery is performed before the aorta gets too big.
In children with MFS/LDS a scoring system called the Z-score is used to index the size of the aorta to the size of the child. This is really important to make accurate decisions about monitoring frequency and the possible need for surgery during years of rapid growth and development.
The Z-score is a calculation that uses the height, weight and size of the aortic root to give a number. This allows the medical team to see how much the size of the aorta differs from the average for someone of the same age, sex and Body Surface Area (BSA).
A normal z-score ranges from –2 to +2. If the z-score is <2 the aortic diameter is below the average, if it is >2 the aortic diameter is above the average and would be considered to be dilated.
Z-score is often also used in clinical trials to monitor the changes in aortic dimensions in response to a new medicine, for example.
