Although saliva, whole blood, serum, plasma, urine, and feces have been used as specimens for SARS-CoV-2 antigen and antibody tests, menstrual blood has not been reported to date. Unlike invasive blood collection methods, menstrual blood collected non-invasively from participants can be used to evaluate the presence of antibodies against SARS-CoV-2. The purpose of our report is to show an association between menstrual blood and the presence of neutralizing antibodies acquired via mRNA vaccination and the usefulness of menstrual blood as a sample type for detecting SARS-CoV-2 antibodies, considering the volume of blood in sanitary napkins as visual napkin score (VNS).
In this study, we collected one napkin each from 40 participants visiting the outpatient gynecology clinic of our university hospital with no symptoms related to COVID-19 and attempted to collect their menstrual blood from the napkins. In 5 of 40 participants, menstrual blood was collected after at least one dose of mRNA vaccination. For this study, the maximum volume of menstrual blood collected was set as 980 μl. In addition, the classification of napkins based on the VNS was set, with level 1 being the lowest percentage of blood on the napkin (0–20%) and level 5 being the highest category (80–100%), according to the consensus of two researchers. We have evaluated used four different antibody testing kits using menstrual blood for detecting IgG and IgM.
The mean amount of menstrual blood collected from the 40 participants' sanitary napkins was 364 ± 372 μl; higher VNS indicated more menstrual blood collected. Statistically, VNS 3 or higher resulted in significantly higher menstrual blood collection than VNS 1 (p<0.01). With VNS 1, the collection of menstrual blood was complicated, and antibody test kits could not be tested for all eight participants. On the other hand, 31 of 32 participants (96.9%) with VNS 2 or higher could be tested with one or more antibody test kits. For all testing kits, 100% of tests with menstrual blood had a positive control line, and all participants who tested positive for IgG and IgM had received a COVID-19 mRNA vaccine. In the five participants after mRNA vaccination, only two of the four testing kits were all positive for IgG.
We have, for the first time, evaluated antibodies against SARS-CoV-2 in menstrual blood collected from sanitary napkins with several antibody test kits. We found that if more than 20% of the napkin area has menstrual blood on it, sufficient menstrual blood can be collected for antibody testing. We also confirmed that menstrual blood collected from a sanitary napkin could be used to detect antibody after mRNA COVID-19 vaccination. We believe that our results are a pioneering effort that has not been reported previously and will lead to better public health and development of wearable devices.
There are no conflicts of interest to disclose for this study.