Renin is a hormone that is released by the kidneys, when blood pressure or blood volume (the amount of blood circulating through your system) is too low. In a nutshell, a high renin level means that mineralorcorticoid treatment is inadequate, and you need to increase the amount of florinef and/or salt.

As Megan says, the release of renin will cause blood pressure to increase. But, in someone with CAH, this means that blood pressure/blood volume is too low, to begin with. It’s part of the body’s built-in system of checks and balances. In essence, the body is trying to self-correct the situation.

A high renin number would generally indicate that the total amount of sodium in your body is too low. However, when you do a bloodtest for sodium, the number that you get back does not reflect total sodium.....rather, it reflects the concentration of sodium in your blood, i.e. the amount of sodium relative to a specific amount of water.

In other words, if you happen to lose sodium and water proportionately, the sodium number can look completely normal, even if you are somewhat dehydrated. By the time the sodium number shows up as being too low, you would be in a crisis situation. Looking at renin, therefore, allows you to detect an imbalance in the system at a much earlier stage in the game.