Oracle Forms

I am using Oracle Forms 6i in Oracle EBS 11.5.10. Say I have 1000 records displayed in detail block. For some records I change the quantity field for some I will not, it will be NULL. When I press the Execute button I am calling an API, passing required fields and API saves the records.

currently, I am using this method to do that.

lb_result := TRUE ;
li_currec := 1;

GO_BLOCK('DETAIL');
first_record ;
lv_isLastRecord := 'N' ;

IF :detail.qty IS NOT NULL
THEN
CALL API.......
ELSE
NULL;

EXIT WHEN :SYSTEM.last_record = 'TRUE';
li_currec := li_currec + 1 ;
next_record;

This works but Form is taking lot of time to do this.

My question is how can I figure out only changed records
(Qty changed) in form and only call the API for those records. Can I use :System.record_status='CHANGED'? Or is there any better way to do than my method.

Please Help.Thank you