I want to use logistic regression on a data set. The y-variable is a binary outcome (yes or no to adverse effects) and the x value is blood concentration of a protein (continous variable). I want to test if higher concentration is related to more frequent adverse effects.

I have 450 observations. 150 observations (1/3 of all observations) have a concentration below the laboratory detection limit (<100 units), the rest lies between 100 to 3500 units.

My question: When doing a logistic regression with these data where 1/3 is "pooled", can I just set these data to be equal to the lowest detectable value (100 units) or do i need to make further adjustments to my regression/data to get the best model.

Thank you in advance