While this question is not related to "Mathematical Optimization and Operations Research with SAS" and while there might be more elegant ways to solve your challenge you might want to use a combination of existing SAS functions to tackle it.
I understand that your orginial variable is a character string containing alphanumeric symbols. Your goal is to read the numeric part and convert it to a numeric variable. Your digit symbol is ".".
The following example might illustrate what you are looking for:
data test;
input string $ 1-22;
length num 8;
digit1=scan(string,1,".");
i=anydigit(digit1,1);
j=anydigit(digit1,-23);
str1=trim(left(substr(digit1,i,j)));
digit2=scan(string,-1,".");
i=anydigit(digit2,1);
j=anydigit(digit2,-23);
str2=trim(left(substr(digit2,i,j)));
all=compress(str1||"."||str2);
num=all;
keep string num;
cards;
14.2 MG/DL
19.2 %
no result 12.13 mmol/l
run;