Elevated blood viscosity is associated with dysautonomia in long COVID symptoms, 2026, Tamariz et al

[forestglip]

Elevated blood viscosity is associated with dysautonomia in long COVID symptoms

Spoiler: Authors

Tamariz, Leonardo; Milanes, Isabela; Bast, Elizabeth; Shehadeh, Lina A.; Klimas, Nancy; Palacio, Ana

Background
Long COVID is associated with elevated inflammatory and antibody levels. Elevated plasma proteins can increase blood viscosity and decrease blood flow. Our aim is to evaluate if blood viscosity is associated with long COVID outcomes.

Methods
We conducted a cross-sectional study and included a sample of patients enrolled in our long COVID clinic. We estimated whole blood viscosity (WBV) using two previously validated formulas and compared it with the NASA lean test, COMPASS-31 scale as measures of dysautonomia and the symptom burden as measured by the modified COVID-19 Yorkshire scale. We obtained WBV at three different shear stress. We divided WBV and evaluated the distribution of symptom scores using univariate and multivariate models.

Results
We included 185 patients for this study. Our sample had a mean age of 56 ± 11 years, included 53% minorities and 32% were women.

The mean C19-YRSm did not change with increasing tertile of WBV (p > 0.05) while the mean COMPASS-31 score increased with increasing tertile of WBV in all levels of shear stress.

In adjusted models the beta-coefficient of the C19-YRSm was (B -0.19p = 0.90) and for COMPASS-31 was (B 7.0 p = 0.01) for 208 s−1 and for all other levels of shear stress Twenty-three percent of patients in tertile 1 had either POTS or orthostatic hypotension compared to 32% on tertile 3 (p = 0.04).

Conclusion
Whole blood viscosity was associated with dysautonomia and not with long COVID symptoms.

Web | DOI | PDF | American Heart Journal Plus: Cardiology Research and Practice | Open Access

 

[Hutan]

It's a shame that we are still seeing studies of lumped Long COVID. This required participants to meet WHO criteria and to have had a diagnosis of Long COVID for at least a year. It makes it hard to make much use of this data.

Participants were consecutive patients at the Miami Veterans Affairs Healthcare System Long COVID clinic.

Participants answered the Elaros COVID-19 Yorkshire Rehabilitation Scale. (17 item)

The Modified C19-YRS (C19-YRSm) is a 17-item patient-reported outcome measure (PROM), with each item rated on a 0-3 numerical rating scale. Zero represents the symptom not being present; 1 represents a mild problem (not affecting daily life); 2 represents a moderate problem (affecting daily life to a certain extent); and 3 represents a severe problem (life disturbing or affecting all aspects of daily life). The C19-YRSm, similar to the original version, is broken down into four sub-scales concerned with the severity of patients’ key symptoms, functional limitations, other symptoms, and overall health. Pre-COVID scores are also captured for comparison. The worst scores for each item (Questions 1-10) sum to give the Symptom Severity sub-scale (score 0-30), Questions 11-15 sum to give the Functional Disability sub-scale (0-15), Question 16 is the other symptoms sub-scale (0-25), and Question 17 is the overall health score (0-10).

The score for 'Anxiety/Mood' is the highest score given for these questions:
Feeling anxious
Feeling depressed
Having unwanted memories of your illness or time in hospital (it's not clear if they are talking about only the acute illness or also the chronic one)
Having unpleasant dreams about your illness or time in hospital
Trying to avoid thoughts and feelings about your illness or time in hospital

There is a PEM question.

This study only used the Symptom Severity subscale - the sum of the worst scores for Questions 1- 10.
For each symptom a rating between 0 and 3 as to how much the symptom affects daily life:
Breathlessness, cough/change of voice, fatigue (tiredness not improved by rest), smell/taste, pain/discomfort, cognition, palpitations/dizziness, PEM, anxiety/mood, sleep (no mention of unrefreshing sleep)

It seems to me that this measure of symptom severity does not cover ME/CFS well.

In fact, because the symptom list is so diverse, I'm not sure it's a good measure of anything much at all.



Measures of dysautonomia were the COMPASS-31 and a NASA lean test.
The COMPASS-31 is another measure that throws all sorts of symptoms in together - and calls them dysautonomia.

 

[Hutan]

I've found this paper difficult to understand, even though there does not seem to be much to it.

Measures of viscosity:
There were two Whole Blood Viscosity measures.

de Simone - calculated from hematocrit and plasma proteins​

Walburn-Schneck model is calculated from shear rate, hematocrit, total protein minus albumin​

I'm not sure yet how they measured the shear rate. I think maybe they just plugged in three different shear rates to cover the different sorts of vascular circulation e.g. in capillaries, artieries. It's quite possible I'm not understanding something here.

A bigger number means more viscosity.

They seem to have divided the patients from the Long Covid clinic into three groups based on their calculated estimated blood viscosities. But, I did not see anywhere where they told us what blood viscosities in healthy people are.

Fifth, we did not measure whole blood viscosity but rather estimated it. However, we used two formulas and the results were consistent.

Well, that's because the inputs in the equations seem to be quite similar. I'm not sure but I think if you are going to say something about blood viscosity in a disease, you really need to measure blood viscosity and tell us how it compares between healthy people and the disease group.

Otherwise, tell us the actual inputs to the equations - tell us what the levels of hematocrit and plasma proteins were. I didn't see these reported anywhere.

 

[Hutan]

They tell us that 10% of the 33.33% of the people with the lower blood viscosity have ME/CFS; 12% of the people with the mid-range blood viscosity have ME/CFS; 14% of the 33.33% of the people with the highest blood viscosity have ME/CFS. That seems to suggest that blood viscosity isn't relevant to ME/CFS. And that might be true, but I'm not getting a whole lot of confidence about the assessments of blood viscosity or the assessments of ME/CFS.

I don't even know if any of the three blood viscosity groups have blood viscosities that aren't normal.

I feel as though I have wasted my time on this. The report badly needed an editor to make the report clearer and more useful. Possibly the study needed a rethink too.

Our study found that increases in whole blood viscosity are associated with dysregulation of the ANS among patients diagnosed with long COVID, and not with long COVID symptom burden.

I'm not surprised they didn't find any pattern of anything using that Yorkshire Rehabilitation Scale for symptom burden. It's a scale that jumbles up different sorts of pathologies and gives you a number that tells you nothing much. In the highest blood viscosity tertile, only 4% were women. They are saying that autonomic dysregulation was more prevalent in that highest blood viscosity tertile. That is surprising.

The discussion says

Another potential explanation could be the fact that the third tertile had a higher proportion of males, and males have higher blood viscosity than females [30]. However, our study calculated adjusted means which accounted for demographics.

Hmm.

The strength of our study includes the use of validated and standardized assessments for other clinical research studies,

Just because the authors of a scale say it's validated and standardised, that doesn't make it useful.

Second, the COMPASS-31 is a subjective measure with many non-specific symptoms that may overlap with other conditions (e.g. dizziness, diarrhea and/or constipation, urinary issues), which may be difficult to interpret in the absence of known dysautonomia.

Yes.

Third, we did not have a control group and therefore are unable to compare blood viscosity with non-long COVID patients to implicate causality.

Yes.

Sorry for my posts. I can't find anything to take from this study.

 

[Turtle]

Sorry for my posts. I can't find anything to take from this study.

Thanks for your input anyway.
Making clear there is not much there is important too.

 

[Felis Catus]

Elevated blood viscosity is associated with dysautonomia in long COVID symptoms

Third, we did not have a control group and therefore are unable to compare blood viscosity with non-long COVID patients to implicate causality.

Thank you @Hutan for reading and analysing the paper.

 

[Sean]

Sorry for my posts. I can't find anything to take from this study.

Nothing to apologise for. This is what needs to be done with all studies and claims. Torn apart and all the flaws and limitations exposed.

It is a core essential part of science, and something to proud of being good at it, which you are.

 

[bscheurle]

It’s a shame the study didn’t include healthy controls. Anecdotally, some patients report having nurses comment on “thick” or “sludgy” blood when they have their blood drawn. It seems like some of us might have rather viscous blood, but that could be true of some healthier people too.