HL7 vs. ASTM for lab instrument interfaces

The short answer

ASTM, now maintained by CLSI as LIS1-A and LIS2-A2, is the long-standing standard for connecting analyzers to an LIS, and it often runs over an RS-232 serial cable. HL7 version 2 is the dominant standard for exchanging orders and results between healthcare systems, and it runs over TCP/IP networks. Many newer analyzers support HL7 as well.

In practice, most labs use both: ASTM or HL7 between instruments and the LIS, and HL7 between the LIS and EHRs, practice systems, reference labs, and billing.

How ASTM works

ASTM instrument messaging is defined in two layers. CLSI LIS1-A, formerly ASTM E1381, handles low-level transmission: the sender requests the line, data moves in short numbered frames with checksums, and each frame is acknowledged. CLSI LIS2-A2, formerly ASTM E1394, defines the message content as a series of records:

• H, the header, identifying the sender and receiver
• P, the patient record
• O, the order record, with the specimen ID and tests
• R, the result record, with value, units, and flags
• C for comments, Q for queries, and L, the terminator

Analyzers can work in two ways. In download mode, the LIS sends orders to the instrument ahead of time. In query mode, the instrument scans a specimen barcode and asks the LIS which tests to run. Both are common, and many instruments support both.

How HL7 version 2 works

HL7 v2 messages are made of segments separated by line breaks, with fields separated by the pipe character. Laboratory messages commonly use:

• MSH, the message header
• PID, patient identification
• ORC and OBR, the order and the requested test
• OBX, one per result value

Orders typically travel as ORM or OML messages and results as ORU^R01, with an ACK confirming receipt. Messages move over TCP/IP using the minimal lower layer protocol (MLLP). For instrument connections, the IHE Laboratory Analytical Workflow (LAW) profile defines how analyzers and LIS systems should use HL7 v2.5.1.

HL7 vs. ASTM side by side

RS-232 vs. TCP/IP

RS-232 and TCP/IP describe how bytes travel, not what the message says. ASTM can run over either. RS-232 is a point-to-point serial cable, still common on established analyzers, and usually needs a serial-to-network device or a local agent to reach a modern server. TCP/IP runs over the lab network and is standard for HL7 and for most newer instruments.

Which should your lab use?

• For each instrument, use what the analyzer supports best. That is usually listed in the vendor’s LIS interface specification. Do not replace a working instrument just to change protocols.
• For EHRs, practice systems, reference labs, and billing, use HL7 v2. It is what those systems expect.
• For a mix of both, use middleware or an LIS interface team that handles ASTM, HL7, serial, and network connections in one place.
• For anything else, flat files or CSV can fill the gap, for example batch results from mass spectrometry software.

Where Lab Dynamo fits

Lab Dynamo builds and supports HL7, ASTM / LIS2-A2, RS-232 serial, TCP/IP, and flat-file interfaces, with code mapping such as LOINC, CPT, and ICD-10. SparkRelay middleware connects instruments of either kind to SparkLIS, PathArray, or nearly any other LIS, including serial-only analyzers through a local relay agent.