Transact SQL :: Save Value Of PREPARE Into A Variable

I have below code:

WHILE i < total_rows DO
SET @param_employee_number = (SELECT employee_number FROM earned_leaves LIMIT i,1);

PREPARE query_statement FROM 'CALL sp_populate_leave_summary(?)';
EXECUTE query_statement USING @param_employee_number;

-- UPDATE earned_leaves SET earned_leave = returned_by_EXECUTE
SET i = i + 1;
END WHILE;

I want to save the value returned by the EXECUTE into a variable in order to use it in the next UPDATE statement.