HL7 vs ASTM for lab analyser interfaces

When an analyser sends a result back to the laboratory information system, it does so in a defined format so the LIS can read the sample ID, each analyte, its value and its flags. In Indian pathology labs that format is almost always ASTM or HL7. Knowing which your instruments speak tells you what an integration project actually involves.

ASTM

The standard began as ASTM E1381 (the low-level transport) and E1394 (the message content), and was later taken over by CLSI as LIS1-A and LIS2-A2 — you will hear all of these names for the same family.

• Transport: typically a serial RS-232 cable between the analyser and the connector PC, though ASTM messages are also tunnelled over TCP on some instruments.
• Framing: messages are wrapped in control characters (STX … ETX) with checksums and ACK / NAK handshaking.
• Structure: records identified by a letter — H header, P patient, O order, R result, C comment, L terminator.
• Typical vintage: the protocol on most older and mid-range haematology and biochemistry analysers.

HL7

HL7 version 2.x (2.3.1, 2.5.1 and so on) is the workhorse healthcare messaging standard, used for analyser results as well as between the LIS, the HIS and an EMR.

• Transport: usually MLLP (minimal lower-layer protocol) over a TCP/IP network connection.
• Structure: pipe-and-hat delimited segments — MSH message header, PID patient, OBR order, OBX one per result value, NTE notes.
• Message types: ORU^R01 carries results back; ORM^O01 / OML^O21 carry orders out to the analyser.
• Typical vintage: newer analysers, networked instruments, and anything that also needs to exchange orders and results with a hospital system.

The practical differences

• Physical setup. ASTM often means a serial cable and a COM port on a PC within a few metres of the machine. HL7 means an IP address and a port, so the connector can sit anywhere on the network.
• Orders. Both support sending orders to the analyser (bidirectional), but HL7’s order messaging is more widely and consistently implemented.
• Ecosystem. HL7 is the same language the LIS uses to talk to an EMR or HIS, so a single HL7 capability covers more of the lab’s interfacing.

Which one you will use

Whichever each analyser supports — it is set by the instrument, not chosen by the lab. A lab with five machines commonly runs some on ASTM over serial and some on HL7 over the network at the same time, with the LIS or its connector normalising both into one report. The useful question for a vendor is not “HL7 or ASTM?” but “here are my exact makes and models — which do you already connect to, and how long does each take?”

(FHIR, the modern HL7 REST API, is worth knowing about but is mostly used between clinical systems today, not for the analyser link itself.)

For how this looks in practice, see how analyser integration works and the analyser integration page.