Background: Quantra is a novel point-of-care (POC) whole blood viscoelastic assay that applies Sonic Estimation of Elasticity via Resonance (SEER). In short, every few seconds ultrasound waves are used to initiate erythrocyte movement, monitor the consequent deviation of these erythrocytes, and determine the shear modulus. The shear modulus surges during clot formation as elasticity (illustrated by erythrocyte deviation) diminishes. The Qplus cartridge reports the parameters (abbreviation; reagents/formula) clot time (CT; kaolin), clot time heparinase (CTH; kaolin, heparinase), clot stiffness (CS; tissue factor), fibrinogen contribution to clot stiffness (FCS; tissue factor, abciximab), clot time ratio (CTR; CT/CTH), and platelet contribution to clot stiffness (PCS; CS-FCS).

Aims: The applicability of a POC assay depends upon its susceptibility to differences in blood composition, including (but not limited to) hematocrit, platelet count, ringer lactate, and acetylsalicylic acid (ASA). We aimed to evaluate the influence of the aforementioned variables on Quantra parameters.

Methods: All experiments were performed in vitro with blood from healthy volunteers. Hematocrit (n=1) and platelet count (n=2) were modified within a range of, respectively, 0.2-0.7 L/L and 50-450 x10⁹/L. Cell counts were not substantially altered (max deviation 12%) after adjustment of hematocrit and platelet count. Whole blood volume was replaced with ringer lactate from 0 up to 60% (n=1) to mimic dilutional coagulopathy and healthy volunteers (n=3) were spiked with 100 µM ASA.

Results: Clot strength parameters were dependent upon hematocrit (negative association), platelet count (positive association), and dilution by ringer lactate (negative association). CT decreased when dilution with ringer lactate exceeded 50%. Quantra parameters were unaffected by ASA-induced platelet inhibition.

The influence of hematocrit (A-D) platelet count (E-H), dilution with ringer lactate (I-L), and acetylsalicylic acid (ASA) (M-P) on Quantra Clot Time (A/E/I/M), Clot Strength (B/F/J/N), Fibrinogen Contribution to Clot Strength (FCS; C/G/K/O), Platelet Contribution to Clot Strength (PCS; D/H/L/P). Blue dots illustrate the unaltered (normal) healthy volunteer samples and reference ranges are presented as grey areas . In case of significant linear regression (p<0.05), the linear regression equation and line/model are presented.

Conclusions: Viscoelastic assessment by Quantra is dependent upon hematocrit, platelet count, and dilution by ringer lactate. These variables should be taken into account when interpreting Quantra results in patients. Additionally, the results suggest Quantra is insensitive for ASA-induced platelet inhibition.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/quantra-the-influence-of-hematocrit-platelet-count-ringer-lactate-and-acetylsalicylic-acid-on-viscoelastic-properties-of-clot-formation/