QMDB samples and sample donors
Where did the samples in the QMDB originate from?
All samples originate from controlled studies conducted by universties or scientific institutes. The largest contributions come from two epidemiological cohort studies of the US National Institutes of Health (NIH): the Baltimore longitudinal study of aging (BLSA) and the Genetic and Epigenetic Signatures of Translational Aging Laboratory Testing (GESTALT). We plan to incorporate more samples from other studies in the future.
Are all samples in the QMDB from healthy donors? How is that defined?
All samples are from individuals who underwent a medical examination and were only included if there were no acute or chronic physical or physiological illnesses known or diagnosed at the time. For the samples originating from large cohort studies of the US National Institutes of Health (NIH), the health status has been defined by the IDEAL standards, see Schrack, J. et al.: “IDEAL” Aging Is Associated with Lower Resting Metabolic Rate: The Baltimore Longitudinal Study of Aging. J Am Geriatr Soc 62:667–672, 2014.
Why can I not select samples from participants with age below 21 or a BMI above 35?
The selection option are limited by the samples present in the database. Currently, no data of samples from individuals under 21 is available. Individuals with a BMI above 35 are not included in the database on purpose because this is a healthy reference database, and these individuals are characterized morbidly obese per definition.
Why can I only select human EDTA plasma as a matrix?
Currently, this is the only matrix included in the QMDB. We plan to expand the database contents regularly in the future.
Why are there so few smokers in the QMDB?
Smoking increases the risk for developing many diseases. As the QMDB is a healthy reference database, individuals with diseases were excluded, and the remaining smokers belong to a minority within the QMDB.
Are age, sex, BMI, and race/ethnicity distributed in the QMDB like in the normal population?
No. Age, BMI, and race/ethnicity are clearly biased in the QMDB as there are generally more elderly Caucasian study participants, and all morbidly obese individuals were excluded from the database.
Why are there so many overweight participants?
The average age of the donors for the QMDB is almost 65 years. Even healthy humans tend to gain weight with age, what leads to an average BMI of 26.5 in the QMDB. This means many participants are overweight and some are obese. This is normal. Morbidly obese individuals (BMI≥35) have been excluded from the QMDB.
What were the preanalytical procedures for the samples included in the QMDB?
Blood sampling was carried out according to established protocols using standard venipuncture procedures. The collection of EDTA plasma in the studies was consistent with guidelines for biomarker studies (Tuck MK, Chan DW, Chia D, Godwin AK, Grizzle WE, Krueger KE et al. Standard operating procedures for serum and plasma collection: early detection research network consensus statement standard operating procedure integration working group. J Proteome Res 2009; 8(1):113–7.). In brief, venous blood samples were collected in the morning, immediately stored at 4°C, and centrifuged within 4 hours. After centrifugation, the plasma was immediately aliquoted and frozen at −80°C. Samples were subject to not more than 2 freeze-thaw cycles prior to metabolomic measurement. Sample quality was checked by assessing metabolite concentrations known to change when these times are not kept. Wherever this quality control showed preanalytical problems, the samples were excluded.
Was the blood collection done AM or PM?
We do not have data for that on all samples. Most of the samples are from the Baltimore Longitudinal Study of Aging, for which the sampling protocol was an AM blood drawing after about 12 h of fasting.