🧬 biology

Epigenetic age profiling of menstrual blood collected using long-term stored Q-Pads

This study demonstrates that dried menstrual blood collected via Q-Pads and stored at room temperature for over two years is a viable, minimally invasive biospecimen for genome-wide DNA methylation profiling and accurate epigenetic age estimation.

Original authors: alejandro caceres

Published 2026-07-21

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: alejandro caceres

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your body keeps a secret diary written in a special chemical ink called DNA methylation. This ink doesn't change your actual genes, but it acts like sticky notes or highlighters that tell your cells which instructions to read and which to ignore. Over time, as you get older, the pattern of these sticky notes changes in a very predictable way. Scientists have figured out how to read these patterns to create "epigenetic clocks," which can tell you how old your cells feel biologically, sometimes even better than your birthday tells you how old you are.

Usually, to read this diary, doctors need to take a blood sample from your arm or, for women, perform a tiny, invasive biopsy of the uterus. But what if you could read this diary using something you already have? Menstrual blood is a unique mix of cells shed from the lining of the uterus, offering a direct window into that specific part of the body. The big question scientists have been asking is: Can we collect this blood at home, let it dry out on a special pad, and keep it sitting on a shelf for years without it rotting, and still read the "age" of the cells inside? If the answer is yes, it could revolutionize how we study women's health, allowing us to track reproductive aging without needing a clinic visit every time.

The Experiment: A Two-Year Shelf-Life Test

In this study, a team of researchers decided to test if a specific product called the "Q-Pad" could survive a long, hot wait. These pads are designed for women to use at home during their period; they have a special strip inside that soaks up the blood. The researchers gathered 16 of these strips that had been sitting in a box at room temperature for more than two years. That's a long time for a biological sample to hang out without a freezer!

Their goal was simple: Could they get enough DNA out of these dried, dusty strips to read the epigenetic clock?

The Results: Not Every Pad Was a Winner, But Some Were Gold

When the team tried to extract the DNA, it was a bit of a rollercoaster. The amount of DNA they got varied wildly. Some strips were like dry leaves, while others were surprisingly rich. Out of the 16 pads they started with:

7 samples didn't have enough DNA to even run the test (they needed at least 500 nanograms).
10 samples passed the initial quality check and were ready for the big machine.
9 samples were confirmed to be from females and were considered "analytically robust" (meaning the data was clean and reliable).

One of the samples that passed the machine test turned out to be a bit of a rebel. While the other 9 showed the expected female patterns, this one looked like it had a mix of male and female markers, or perhaps a missing chromosome. The researchers set this "outlier" aside for their main analysis, but it actually taught them something interesting: even this messy sample still managed to tell the truth about its age.

The Big Discovery: The Clock Still Ticks

Despite the samples being dried out and sitting on a shelf for over two years, the magic happened when they ran the numbers. The "epigenetic clocks" they used to estimate biological age worked surprisingly well.

The Horvath Clock: This was the star of the show. It predicted the women's ages with incredible accuracy, missing by an average of only 2.2 years. The connection between the predicted age and the real age was extremely strong (a correlation of 0.965).
The AltumAge Clock: This one, which is usually great for uterine tissue, also worked but was a bit less precise here, missing by an average of 6.8 years.
The Others: Two other clocks also showed a link to the real ages, though they weren't as sharp as the Horvath clock.

Essentially, even though the samples were old and dried, the chemical "sticky notes" on the DNA hadn't scrambled so badly that the age was lost. The cells remembered how old they were.

A Side Quest: The X-Chromosome Mystery

The researchers also looked at a specific marker called XRa, which checks if the X-chromosomes (the ones that determine female biology) are behaving correctly. In healthy females, this number usually sits between 5 and 15.

The 9 reliable female samples had XRa values between 8.5 and 14.4, which is exactly what you'd expect.
The "rebel" outlier sample had a value that looked like a male or someone with a missing chromosome, confirming that the test could spot biological oddities even in these old samples.

Interestingly, the researchers noticed that the samples with higher XRa values seemed to have slightly older epigenetic ages, but they are careful to say this is just a hint for future studies, not a final rule.

What This Means (and What It Doesn't)

This study suggests that dried menstrual blood collected at home and stored at room temperature is a promising tool. It proves that you don't always need a freezer or a clinic visit to get high-quality data about reproductive aging.

However, the authors are very honest about the bumps in the road. Because they only used one strip per person (the other was used up in a different test), they didn't always get enough DNA. They also noted that the long storage time might have damaged some samples. This was a small "pilot" study with only 16 people, so while the results are exciting, they aren't the final word yet.

In short, the paper suggests that the Q-Pad is a viable "time capsule" for DNA. It's not a perfect system yet, but it's a strong step toward a future where women can track their reproductive health by simply mailing in a dried pad from their bathroom, rather than visiting a doctor's office.

Technical Summary: Epigenetic Age Profiling of Menstrual Blood Collected Using Long-Term Stored Q-Pads

Problem Statement
Assessment of reproductive health and fertility currently relies on invasive or indirect methods, such as venous blood sampling, transvaginal ultrasonography, and endometrial biopsies. These approaches limit the feasibility of longitudinal monitoring, particularly as the age of childbearing increases and the use of assisted reproductive technologies expands. While menstrual blood offers a unique, non-invasive source of endometrial-derived cells and immune populations, self-collected biospecimens suitable for large-scale genome-wide DNA methylation studies have been limited. Specifically, it was previously unestablished whether DNA recovered from dried menstrual blood collected via Q-Pads and stored at room temperature for extended periods (over two years) could support high-quality epigenetic profiling.

Methodology
This pilot study assessed the feasibility of extracting DNA and performing genome-wide methylation profiling on 16 residual Q-Pad specimens. These samples were originally collected in 2022–2023 for an HR-HPV detection study, stored at room temperature at Qurasense, Inc. (Qvin) for over two years, and shipped to the Barcelona Institute for Global Health (ISGlobal) in 2026.

Sample Processing: DNA was extracted from the dried menstrual blood strips using the QIAamp DNA Blood Mini Kit. Quantification and purity were assessed via Qubit and NanoDrop.
Methylation Profiling: Genome-wide DNA methylation was performed using the Illumina Infinium MethylationEPIC v2.0 BeadChip. Input DNA was 500 ng where available. Bisulfite conversion was conducted using the EZ-96 DNA Methylation MagPrep Kit on a KingFisher Flex platform.
Data Analysis: Raw data were processed in R using minfi and MethylCallR. Quality control (QC) involved filtering probes with detection P-values >0.01, low bead counts, cross-hybridization, and mapping issues. Functional normalization was applied to retained probes.
Epigenetic Metrics: Epigenetic age was estimated using four established clocks (AltumAge, Horvath, Zhang, and PhenoAge) via the pyaging package. Additionally, X-chromosome inactivation (XCI) status was assessed using the XRa biomarker to quantify defective XCI maintenance.

Key Results

Sample Viability: DNA yield and purity varied significantly. Six samples had optimal A260/A280 ratios (1.7–2.0), but seven samples failed to meet the recommended 500 ng input threshold. Despite this, all 16 samples were processed.
Quality Control: Ten of the 16 samples passed array-level QC (mean CpG call rates >95%). One of these ten samples showed discordant epigenetic sex prediction (higher Y-chromosome calls) and global hypomethylation, identifying it as an outlier.
Robust Dataset: After excluding the sex-discordant outlier, nine samples were retained as analytically robust female samples for biological interpretation.
Epigenetic Age Correlation: Multiple clocks correlated with chronological age. The Horvath clock demonstrated the strongest performance with a mean absolute error (MAE) of 2.2 years, a Spearman correlation ( $\rho$ ) of 0.965, and $P = 2.54 \times 10^{-5}$ . The AltumAge clock was also significant but showed lower accuracy in this set (MAE = 6.8 years, $\rho = 0.765$ ).
X-Chromosome Analysis: XRa values for the nine robust female samples fell within the expected female range (5–15), ranging from 8.5 to 14.4. The outlier sample showed an XRa value consistent with male profiles or X-chromosome monosomy. When dichotomized at an XRa threshold of 10, AltumAge estimates differed significantly between groups ( $P = 0.036$ ).

Key Contributions

Feasibility Validation: The study establishes that dried menstrual blood collected via Q-Pads and stored at room temperature for over two years can yield genome-wide DNA methylation profiles suitable for downstream analysis.
Biomarker Recovery: It demonstrates that biologically informative signals, including epigenetic age and X-chromosome inactivation status, are preserved despite prolonged ambient storage.
Methodological Benchmark: The work provides a proof-of-concept for using self-collected, room-temperature stored menstrual blood in cohort-scale epigenetic studies, highlighting the importance of rigorous QC to identify outliers (e.g., sex discordance).

Significance and Claims
The authors claim that these findings support dried menstrual blood as a "promising minimally invasive biospecimen" for reproductive aging and endometrial health studies. The ability to estimate epigenetic age suggests that molecular readouts relevant to reproductive biology can be preserved without cold-chain logistics.

However, the paper maintains a modest tone regarding its conclusions:

The results are presented as a pilot study with a small sample size ( $N=9$ robust samples), and the authors explicitly state that the clock performance comparisons should not be interpreted as a formal benchmark.
The association between XRa and epigenetic age is described as "exploratory" and requires validation in larger, phenotyped datasets.
Limitations are acknowledged, including variable DNA extraction yields, the potential impact of prolonged room-temperature storage on degradation, and the lack of matched peripheral blood or endometrial tissue for direct comparison.

The study concludes that while pre-analytical optimization and larger longitudinal validation are necessary, this approach offers a scalable route for studying reproductive aging and endometrial biology using genome-wide DNA methylation.