The Three Phases of Laboratory Testing: Pre-Analytical, Analytical and Post-Analytical

Every laboratory result is the product of a long chain of steps that begins and ends with a clinical decision. George Lundberg famously described this as the “brain-to-brain loop”: a question forms in the clinician's mind, a sample is taken and tested, and a result returns to inform care. Modern quality management divides that loop into the total testing process (TTP) and its three phases — pre-analytical, analytical and post-analytical. Understanding how they fit together is the foundation of laboratory quality, because a failure in any one phase can invalidate the whole result.

The Total Testing Process at a Glance

The three phases map to the sample's journey and are the same three phases that ISO 15189:2022 calls pre-examination, examination and post-examination:

• Pre-analytical — everything before measurement: ordering, patient preparation, collection, identification, transport, receipt and storage.
• Analytical — the measurement itself, on a calibrated, quality-controlled analyser.
• Post-analytical — validation, interpretation, reporting and communication of the result to the clinician.

The Pre-Analytical Phase

The pre-analytical phase is the longest and most fragmented. It spans multiple people and locations — often outside the laboratory's direct control — and it is where the great majority of errors occur. In the classic analyses by Plebani and Carraro, roughly 62% of laboratory errors were pre-analytical, compared with about 15% analytical and 23% post-analytical. Later work continues to place the pre-analytical phase at the top, commonly cited as up to ~70% of all errors.

Typical failures include patient or sample misidentification, hemolysis, clotting, insufficient volume, wrong tube type and transport delays or temperature excursions. We cover this phase in depth in our pre-analytical errors guide and explain why it is so error-prone.

The Analytical Phase

The analytical phase is the part most people picture when they think of a laboratory: the sample on the analyser. It is also the most controlled. Decades of automation, standardisation, calibration and internal/external quality control have driven analytical errors down to a relatively small share of the total. Remaining risks include calibration drift, reagent problems, method limitations and interference carried over from the pre-analytical phase — for example, hemolysis that distorts a potassium result.

The Post-Analytical Phase

The post-analytical phase turns a measurement into clinical information: technical validation, interpretation, release, and reporting to the right clinician — including timely notification of critical values. Errors here include reporting to the wrong record, delays, missing critical-value alerts, and results that are technically correct but poorly communicated or misinterpreted. Because this phase closes the brain-to-brain loop, a failure here can undo a perfect measurement.

Why the Pre-Analytical Phase Dominates Errors

The imbalance is structural, not accidental. The analytical phase happens on standardised instruments under continuous QC. The pre-analytical phase depends on manual steps performed by many people — phlebotomists, nurses, couriers, reception staff — across clinics, wards and vehicles, frequently with little visibility back to the laboratory. That combination of manual work, many hand-offs and low visibility is exactly what makes errors both common and hard to detect.

How the Three Phases Interconnect

The phases are a chain, and the weakest link sets the quality of the result. A flawless analytical run cannot rescue a hemolysed or misidentified sample. Correct interpretation in the post-analytical phase often depends on knowing what happened earlier (“result affected by hemolysis”). This is why ISO 15189:2022 treats all three phases as one process and applies risk-based thinking across the whole loop rather than to the analyser alone.

Where Sample Tracking Helps Most

Because the pre-analytical phase carries the most error — and the least visibility — it offers the largest quality gains. End-to-end sample identification and tracking make each hand-off visible and attributable: verified identity at collection, continuous transport monitoring, documented receipt, and a complete chain of custody. That both prevents pre-analytical errors and gives the post-analytical phase the context it needs to interpret results correctly. For how this maps onto the standard, see our ISO 15189:2022 Section 7 guide.

Frequently Asked Questions

What are the three phases of laboratory testing?

Pre-analytical (ordering, collection, identification, transport, receipt and storage), analytical (the measurement on the analyser), and post-analytical (validation, interpretation, reporting and communication). ISO 15189:2022 calls them pre-examination, examination and post-examination.

What is the total testing process (brain-to-brain loop)?

The total testing process, or Lundberg's “brain-to-brain loop,” describes laboratory testing as a full cycle from a clinician's question through collection, analysis and reporting back to a clinical decision. It emphasises that quality depends on every step, not just the measurement.

Which phase has the most errors?

The pre-analytical phase. Classic studies attribute about 60–70% of laboratory errors to it, versus roughly 15% analytical and the remainder post-analytical, because it involves the most manual steps and hand-offs with the least visibility.

Why is the analytical phase the most reliable?

Because it runs on standardised, automated instruments under continuous internal and external quality control — conditions that the manual, distributed pre-analytical phase rarely matches.

See how S4DX brings visibility to the total testing process.