As of now, the most recent instrument-to-LIS Interface standard is called LAW. (Lab Automation Workflow, Google it for more details). However, using this standard for your instrument it willl limit it’s operability to recent versions of LIS that implement LAW.
There are two other standards (HL7 and ASTM E1394-97) that are more widely implemented, but are also considered obsolete. Nevertheless, both are capable of describing the most complex messaging needs for modern laboratory instrumentation, such as results from multiplex assays.
The ASTM standard is the most widely used, as it is supported by both recent and ancient LIS versions.