Erythrocyte Sedimentation Rate: A Physics-Driven Characterization in a Medical Context

Summary

Erythrocyte sedimentation rate (ESR) is a physical parameter, often used in routine health checks and medical diagnosis. A theoretical model that allows to extract physically-meaningful parameters from the whole sedimentation curve, based on modern colloidal knowledge, has recently been developed. Here, we present a protocol to automatically collect the ESR over time, and extract the parameters of this recent model from this automated data collection. These refined parameters are also likely to improve the medical testimony.

Abstract

Erythrocyte (or red blood cell) sedimentation rate (ESR) is a physical derived parameter of blood which is often used in routine health checks and medical diagnosis. For instance, in the case of inflammation, a higher ESR is observed due to the associated increase in fibrinogen and other plasma proteins. It was believed that this increase was due to the formation of larger aggregates of red blood cells (RBCs) caused by the increase in fibrinogen. Indeed, fibrinogen is an agent-fostering aggregation of RBCs and in the Stokes regime-assumed to be observed in blood-larger aggregates sediment faster. However, all models of ESR measurements based on this hypothesis require further specific physical assumptions, not required in any other system. Besides, modern studies in the field of colloidal suspensions have established that attractive particles form percolating aggregates (i.e. aggregates as wide as the container). The sedimentation of these colloids then follows a so-called "colloidal gel collapse". Recently, it has been shown that RBCs actually follow the same behavior. This hypothesis also allows to efficiently and analytically model the sedimentation curve of RBCs, from which robust and physically-meaningful descriptors can be extracted. This manuscript describes how to perform such an analysis, and discusses the benefits of this approach.

Introduction

The erythrocyte sedimentation rate (ESR) is a medical in vitro clinical tool, formally introduced in evidenced-based medicine during the twentieth century^1,2,3,4. It is currently used worldwide as a nonspecific inflammatory test, or to monitor the evolution of some specific conditions^5,6,7,8. This is mainly due to an increase in the fibrinogen concentration, but also in other plasma components such as IgM<....

Protocol

Blood sample collection and experiments were approved by the "Ärztekammer des Saarlandes", ethics votum 51/18, and performed after informed consent was obtained according to the Declaration of Helsinki. Standard measurements should be performed with ethylenediaminetetraacetic acid (EDTA)-anticoagulated blood (standard EDTA concentration of 1.6 mg/mL blood, European norm NF EN ISO 6710), in Westergren tubes. The volume required to fill the Westergren tube depends on the manufacturer (as lower parts sometimes contain a wider reservoir); The volume should be about 1 mL of full blood, and 800 µL for the tubes indicated in the Table of Materials

Results

An example of an image sequence correctly acquired is provided as Supplementary Movie 1 (MovieS1.avi). A series of characteristic fits of the model is shown for various conditions in Figure 2. Fibrinogen concentration was determined from the fibrinogen concentration in the plasma Fib₀, assuming that the serum does not have any fibrinogen at all. Hence, Fib = C Fib₀, where C is the plasma volume fraction in the plasma-.......

Discussion

For the automated protocol to work efficiently, it is important to have a clear background and proper illumination. A dark background might prevent the existence of an efficient binarization threshold. For samples with some hemolysis, which usually occurs (increases) over time, it is important to verify first that the chosen binarization threshold is relevant for both the initial and final pictures.

When it comes to the binarization process of the picture, the choice of the ROI and binarizatio.......

Materials

Name	Company	Catalog Number	Comments
Anticoagulant (EDTA or Heparin) tube (for blood sample)	SARSTEDT	267001 or 265	Anticoagulated blood sample to characterize
Camera EOS M50	Canon	Kit EF-M18-150 IS STM	Any camera should work, provided that sector alimentation, connection to computer for automated shooting and adapted objective are available
Centrifuge	HERMLE	302.00 V03 - Z 36 HK	Requirements: at least 3000 x g ofr 7 min.
Micro-centrifuge	MLW	TH21	or any other way to determine the hematocrit
Micro-hematocrit capilaries	Fisher scientific	11884040	or other capillaries/containers for hematocrit determination
Phosphate Buffered Saline (PBS)	ThermoFisher	10010023	1x PBS, pH 7.4, 298 Osm
Pipettes (e.g. positive displacement pipette)	Gilson	FD10006	Pipette required to manipulate blood and/or packed cells.Other models are of course suitable, but be careful to treat blood and pakced cells as highly viscous fluids.
Wax sealing plate	Hirschmann	9120101	Sealing wax for the micro-hematocrit capillaries
Westergren tubes	Praxindo	A9244560	Any other standard Wetsergren tube should work too
White background with illumination	/	/	White sheet(s) of paper behind the samples, with usual room light is perfcetly sufficient.