Castro-Marrero, Jesús, Zacares, Mario, Almenar-Pérez, Eloy et al. · Journal of clinical medicine · 2021 · DOI
Researchers analyzed blood samples from 250 women with ME/CFS to see if specific blood markers could help identify different types of the disease. They found that about 43% of participants had high levels of a protein called C1q, which was particularly associated with those experiencing more pain symptoms. This discovery suggests that blood tests might one day help doctors identify which ME/CFS patients belong to which subgroup, potentially leading to better tailored treatments.
ME/CFS currently lacks objective diagnostic tests and relies entirely on clinical symptoms, making diagnosis challenging and variable across providers. Identifying blood-based markers like C1q could enable earlier, more accurate diagnosis and reveal disease subtypes that might respond differently to treatments. This work provides a foundation for developing laboratory tests that could revolutionize ME/CFS clinical management and accelerate targeted research.
This study does not prove that C1q causes ME/CFS or pain symptoms—it only shows an association in this cross-sectional snapshot. The findings are specific to women and cannot be assumed to apply to men with ME/CFS. The study does not establish whether C1q elevation is a consequence of ME/CFS, a contributing factor, or an unrelated marker in a subgroup.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Castro-Marrero, Jesús, Zacares, Mario, Almenar-Pérez, Eloy, Alegre-Martín, José, & Oltra, Elisa (2021). Complement Component C1q as a Potential Diagnostic Tool for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Subtyping.. Journal of clinical medicine. https://doi.org/10.3390/jcm10184171
BibTeX
@article{mecfsatlas-castro-marrero-2021-complement-component,
author = {Castro-Marrero, Jesús and Zacares, Mario and Almenar-Pérez, Eloy and Alegre-Martín, José and Oltra, Elisa},
title = {Complement Component C1q as a Potential Diagnostic Tool for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Subtyping.},
journal = {Journal of clinical medicine},
year = {2021},
doi = {10.3390/jcm10184171},
note = {PubMed: 34575280},
url = {https://www.mecfsatlas.com/evidence/castro-marrero-2021-complement-component},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/castro-marrero-2021-complement-component
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