Why are labs still running a test for inflammation with a 4-hour time limit?

Every blood sample begins degrading the moment it's drawn, and most of what can go wrong with a laboratory result goes wrong before the specimen ever reaches an analyzer. This is the preanalytical phase — collection, handling, transport, storage — and it is estimated to account for the large majority of laboratory errors, far more than the analytical step that labs spend most of their energy perfecting. Hemolysis from a rough draw, a mislabeled tube, a delayed courier, or an ambient temperature swing are the quiet failure points, and they rarely announce themselves. A compromised sample usually comes back not as an error message but as a plausible-looking number.

Different tests tolerate this gauntlet differently. A complete blood count (CBC) is forgiving, generally good for a day or so at room temperature. Glucose, however, is not, as it falls quickly in an uncentrifuged tube unless a preservative holds it, while potassium leaks from cells and drifts within hours. Each analyte has its own clock, and one of the shortest clocks in all of routine hematology belongs to a test that clinicians order constantly to assess all sorts of inflammation: the erythrocyte sedimentation rate (ESR).

The sed rate has one of the shortest stability windows in routine hematology. ALCOR Scientific examined how the technology to fix the instability already exists, and why laboratories have yet to embrace it.

An anomaly hiding in plain sight

Guidance from the Clinical and Laboratory Standards Institute and the International Council for Standardization in Haematology holds that a Westergren ESR (the original ESR testing method) must be run within four hours of collection at room temperature, or within 24 hours if refrigerated. Although the manual Westergren method is becoming increasingly less common due to staffing shortages, most other ESR methods are based on the principles of Westergren and rely on gravity-based sedimentation. With laboratory testing becoming more centralized, four hours is a severe constraint for such a routine test, and it stands out precisely because the sed rate is drawn from the same lavender-top tube as the day-stable CBC.

The fragility is inherent to what the test measures. The ESR doesn't quantify a molecule; it measures a behavior — how fast red blood cells settle through plasma over an hour. When there is increased protein in the bloodstream due to an inflammatory condition, cells will aggregate and settle more – therefore high ESR values can signify inflammation. Erythrocyte sedimentation is a transient phenomenon confined to fresh blood. Blood left sitting in a tube keeps changing, altering how the red blood cells aggregate and sink. The longer the wait, the further the measured rate drifts from the patient's real physiological state. Refrigeration slows the drift but doesn't stop the clock.

That four-hour window of room temperature stability was trivial to meet when the sed rate was run down the hall from the phlebotomy chair, but it is much harder now. Modern testing is consolidated: Samples are collected at scattered clinics and patient-service centers, then trucked to a central lab in vehicles that are not temperature-controlled in any real sense. The trip can run warm or cold, and the four-hour limit is one few people downstream ever see. The result still gets reported and is used to assist in diagnosing and monitoring rheumatoid arthritis, polymyalgia rheumatica, giant cell arteritis, and other inflammatory diseases, where a value nudged across a threshold by transport time can change how a patient is classified and treated.

The fix exists

Here's what makes the persistence of the four-hour method genuinely puzzling: The constraint is not a law of nature, but an artifact of how the ESR has traditionally been measured. The testing methodology (Westergren-based) creates the limitation.

A study published in August 2026 in Diagnostics compared the classical Westergren column against an automated analyzer, the iSED, which uses photometric rheology. Instead of waiting an hour to watch cells fall, it optically captures the first seconds of red-cell aggregation inside a temperature-controlled flow cell, returning a result in about 20 seconds. Samples run this way held accurate for up to 28 hours at room temperature and 48 hours refrigerated. Westergren samples, by contrast, showed signs of deterioration within several hours — not surprisingly since the guidelines have long been set at four hours stability for this methodology. Reading the earliest kinetics of aggregation in a controlled chamber, the newer method largely sidesteps the slow morphological decay that undermines a Westergren-based reading.

Extend the window from four hours to more than a day, and the preanalytical headache mostly dissolves: fewer samples rejected out of window, fewer redraws, fewer second needle-sticks, and the option to run ESR and CBC from a single tube instead of a dedicated draw. All this results in a real savings on consumables and labor, as lab staffing shortages deepen.

So why the inertia?

Part of the answer is that the Westergren method is the internationally recognized reference standard, and reference standards are sticky by design: Labs validate against them, regulators recognize them, and clinicians trust the familiar. Another part is capital and workflow; replacing an installed method means budget, procurement, verification, and retraining, none of it free. The last part is simply that the preanalytical phase is chronically underscrutinized. Laboratories audit calibration to fractions of a percent while leaving specimens to fend for themselves in the back of a van, so a stability limit baked into an old method rarely rises to the top of anyone's priority list.

The extended stability window is specific to the photometric method, not a new fact about ESR samples in general; a Westergren sample is still a four-hour proposition. The iSED analyzers measure a different part of the sedimentation process while also shielding the sample from environmental variables and standardizing the testing process through full automation. When a clinician orders an ESR test, they may not be aware of the method in use by the testing laboratory.

But the underlying question stands on its own. When a routine test carries one of the tightest stability windows in the lab, when that window is routinely blown by the ordinary realities of sample transport, and when a method exists that relaxes the constraint by a full day, "because we've always done it this way" starts to look less like caution and more like inertia. Four hours is shorter than a lot of the trips these samples are expected to survive, and it may be time to ask why laboratories continue to retain old methodology when a better solution is readily available, inexpensive and easy to use.

This story was produced by ALCOR Scientific and reviewed and distributed by Stacker.