In the answer area (IXGANSAA) returned by IXGWRITE, bit Ansaa_WriteTriggersReturned indicates that the Ansaa_WriteTriggers section has been filled in.
The write triggers are returned for successful IXGWRITE requests (RETCODE = 0 or 4) and show log stream primary storage consumption information.
ANSAA_STRUCTUSEPERCENT is returned for coupling facility structure
based log streams and indicates the percentage of CF structure elements
in use (between 0 and 100) 
for the log stream.
ANSAA_STAGINGUSEPERCENT is returned for DASDONLY log streams and for CF structure based log streams that duplex to staging data sets. The value indicates the percentage of staging data set space in use (between 0 and 100).
The flags ANSAA_WRITEABOVEHIGHOFFLOAD, ANSAA_WRITEELEVATEDCAPACITY
and ANSAA_WRITEIMMINENTCAPACITY are filled in based on current primary
storage usage and log stream definition HIGHOFFLOAD percentage. For
CF structure based log streams, the flags are based on ANSAA_STRUCTUSEPERCENT.
For DASDONLY log streams, the flags are based on ANSAA_STAGINGUSEPERCENT.
ANSAA_WRITEABOVEHIGHOFFLOAD indicates the usage is greater than HIGHOFFLOAD. ANSAA_WRITEELEVATEDCAPACITY indicates the usage above
the 1/2 point between HIGHOFFLOAD and the log steam imminent threshold.
ANSAA_WRITEIMMINENTCAPACITY indicates the usage
above the imminent threshold. The derived value for the imminent threshold
is the 2/3 point between HIGHOFFLOAD and 100% full.