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Also called: ESR analyzer, ESR machine, Erythrocyte sedimentation rate

ESR Analyser: Automated ESR Machines and the Westergren Method

The erythrocyte sedimentation rate is an old, simple test that clinics still order every day. How it is measured, what automated analysers change and what to check before buying one.

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What the ESR measures

The erythrocyte sedimentation rate (ESR) is how far red cells settle in a vertical column of anticoagulated blood in one hour, reported in millimetres per hour. Inflammation raises proteins such as fibrinogen that make red cells stack together and fall faster, so the ESR is a non-specific marker of inflammation. It is not part of the standard FBC: most haematology analysers do not report it, although a few laboratory models now combine the two.

The Westergren method

  • The reference method recommended by the International Council for Standardization in Haematology (ICSH).
  • Blood is diluted with sodium citrate — or EDTA blood is diluted in the modified method — and drawn into a 200 mm graduated tube held exactly vertical.
  • After 60 minutes, the height of clear plasma at the top is read in millimetres.
  • The result is affected by tube tilt, room temperature, vibration, direct sunlight and delay before testing.
  • It is cheap but slow, uses open tubes that expose staff to blood, and depends on careful timing and reading.

Automated ESR analysers

Methods differ, but the aim is the same: a Westergren-equivalent result with less handling and less waiting. Many automated systems report in under 30 minutes, and some far faster.

Automated Westergren

Racks of Westergren-type tubes are read by an optical sensor, removing manual timing and reading. Some read early and extrapolate to a 60-minute equivalent.

Closed-tube systems

The analyser measures sedimentation in the collection tube itself — in some systems the same EDTA tube used for the FBC — so there is no extra tube and no open blood.

Kinetic or photometric methods

Some analysers measure how quickly red cells aggregate in a narrow flow cell, within minutes or less, and convert the reading to a Westergren-equivalent value.

Questions to ask before buying

  • Which method does it use, and what published comparison with Westergren supports it?
  • Which tube does it need — citrate, the EDTA tube used for the FBC, or its own?
  • How many samples per run and per hour, and how long to the first result?
  • Are there limits on sample age or haematocrit, and how are very high results handled?
  • How is QC run, with which control material, and how often?
  • Can results be sent to your LIS or clinic system?
  • MDA registration numbers for the analyser, its tubes and its controls.

Read next Connecting analysers to your clinic systemQuality control basics

Where ESR fits in a clinic

Alongside the FBC

Doctors often request an ESR with an FBC. Where an automated ESR analyser reads from the EDTA tube, a clinic already running FBCs in-house can add the ESR without a second draw.

ESR and CRP

C-reactive protein (CRP) rises within hours of inflammation and falls quickly, while the ESR changes more slowly. They answer slightly different questions, and CRP is measured on a chemistry or point-of-care analyser.

Point-of-care CRP analysers

One method over time

Automated and manual methods can disagree for some samples, especially at high values. Keep the same method when following a patient, and use reference intervals that apply to that method.

Related guides

Haematology Analyser Quality Control and CalibrationThe routine that keeps every FBC result trustworthy — from the morning control run to external quality assessment and accreditation.Point of Care Blood Analyser Options vs a Full FBC AnalyserSmall finger-prick analysers answer one question quickly; a haematology analyser answers many. Here is how to tell which your clinic needs.EDTA Blood Samples: Handling That Protects Every FBC ResultMost wrong FBC results start before the sample reaches the analyser. A step-by-step guide to the tube, the draw, the mix and the wait.

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Frequently asked questions

Does a haematology analyser measure ESR?
Most do not — the ESR needs its own method. A few laboratory analysers combine FBC and ESR, and some automated ESR analysers read directly from the same EDTA tube.
How long does an automated ESR take?
It depends on the method. Many automated systems report in under 30 minutes, compared with 60 minutes for the manual Westergren method.
Are automated ESR results the same as Westergren?
They are designed to agree closely with Westergren, but agreement varies by method and sample, particularly at high values. Ask for comparison data and use the reference intervals for your method.
What affects a manual ESR result?
Tube tilt, room temperature, vibration, under-filled or clotted samples and delays before testing all change the result — one reason many labs automate it.

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