Identifying the Ideal Blood Donor

Large-scale study sheds light on how donor characteristics impact blood storage

Each day, more than 36,000 blood transfusions are performed in the United States.1 Blood storage is an essential part of the transfusion chain and helps maintain the quality of blood donations over time. Despite regulated storage conditions, red blood cells experience morphologic and metabolic changes that make them more susceptible to hemolysis.2

The Different Types of Hemolysis

Osmotic hemolysis: In a hypotonic environment, an influx of water into red blood cells causes them to swell. The increase in pressure compromises the integrity of the cell membrane and allows hemoglobin to escape.
Oxidative hemolysis: Red blood cells undergo oxidative stress in the presence of reactive oxygen species, which can oxidize lipids leading to membrane instability and cell death.
Spontaneous hemolysis: the processing and storage process following blood donation can injure red blood cells by damaging the cell membrane, making the cells more susceptible to lysis.

Transfusing hemolyzed red blood cells into patients leads to rapid clearance of these damaged cells through the liver or spleen. The products released from these cells, such as iron, can be repurposed for future red blood cell production. However, clearing too many of these cells too quickly can lead to a rapid accumulation of iron resulting in bacterial growth, a pro-inflammatory response, and other complications.3

Not all blood samples experience hemolysis in the same way. There are three types of hemolysis—osmotic, oxidative, and spontaneous—and different amounts of each can be found in blood samples from different donors. Researchers are now working to understand whether individual donor characteristics such as body mass index, alcohol consumption, genetics, or hormone intake could explain these differences.

REDS-III: Understanding the transfusion chain

Questions about red blood cell storage have been asked for decades. In 1989, the National Heart, Lung, and Blood Institute launched the Retrovirus Epidemiology Donor Study (REDS) to assess blood donation and transfusion safety and efficacy in response to the HIV/AIDS epidemic. Since then, the study’s focus has shifted to Recipient Epidemiology and Donor Evaluation (REDS)-III, investigating all elements of the blood transfusion chain from the donor to the products made, and finally into the recipient.4

REDS-III collected data from four blood centers and 12 hospitals across the United States from July 2012 to December 2016. The study included more than 2.5 million blood donations, over 6.5 million blood products, close to 235,000 transfusions in over 120,000 recipients, and approximately 1.3 million non-transfused control patients. This project established the first-ever detailed research database that links blood donors and their donations to the transfusion recipients.5 The wealth of information collected through REDS-III has provided a valuable resource in this research area.

To investigate specific donor characteristics and their impact on hemolysis, RBC-Omics was initiated as part of the larger REDS-III project. RBC-Omics assessed behavioral, genetic, and biochemical characteristics in 13,403 diverse blood donors and linked this information to their blood products and transfusion recipients.6 Through this work, researchers have access to detailed molecular information about the patients and blood samples and have been able to ask new questions. 

Genetic variability and hemolysis

One of the first analyses of the RBC-Omics samples looked at intradonor hemolysis variability in 664 study participants.7 The researchers evaluated hemolysis in two blood samples given by the same donor at different times following cold storage. The study demonstrated that spontaneous hemolysis was not reproducible, but osmotic and oxidative hemolysis were similar between the two samples. This consistency suggested that these two types of hemolysis were related to the donor, not the processing and storage conditions, and could be associated with heritable traits.

A recent study investigated potential genetic markers that could explain this intradonor reproducibility.8 The researchers looked at correlations between the three different types of hemolysis and genetic variants. Through this work, they identified 27 genetic loci associated with hemolysis, many of which were found in candidate genes known to modulate metabolism and ion channels. Of these variants, 21 were associated with osmotic hemolysis. An additional five were associated with oxidative hemolysis, including several genes encoding antioxidant enzymes. These results begin to explain the potential heritability of hemolysis.

Sex-related differences

Another of the initial RBC-Omics analyses looked at the correlation between hemolysis and ethnicity, sex, and age.9 The results showed that male sex was associated with an increase in all three types of hemolysis—oxidative, osmotic, and spontaneous. Researchers have investigated hormones as one potential explanation for these sex-based differences.

In one study of the RBC-Omics cohort, researchers looked at hemolysis in blood donations from premenopausal women taking birth control compared with premenopausal women not on birth control and postmenopausal women receiving hormone replacement therapy (HRT) versus those not on HRT.10 The results showed a reduction in spontaneous hemolysis across the entire cohort of pre and postmenopausal women taking hormones compared with the controls. Researchers also saw a reduction in osmotic hemolysis in postmenopausal women on HRT compared with postmenopausal women not on HRT and a reduction in oxidative hemolysis in premenopausal women taking estrogen compared with premenopausal women not taking estrogen. The overall results suggest a protective effect of estrogen against hemolysis.

Another analysis of the RBC-Omics data investigated the impact of testosterone and red blood cell susceptibility to hemolysis during cold storage.11 The study looked at blood donations from men taking testosterone replacement therapy. The results showed increased susceptibility to osmotic hemolysis, a trend toward increased spontaneous hemolysis, and decreased oxidative hemolysis. Based on these results, testosterone could explain the increased osmotic and spontaneous hemolysis in men compared to women.

Future directions

REDS is now in its fourth phase. REDS-IV-P will build on REDS-III with an additional focus on research with newborns, children, and pregnant women who need transfusions.4 This work will help inform blood policy decisions for young recipients and other understudied populations.

Understanding what donor characteristics contribute to hemolysis could help researchers uncover what leads to this phenomenon in stored blood samples. This information could also help identify “super donors” whose red blood cells are less prone to hemolysis during cold storage and increase the integrity of the blood supply.


  1. Importance of the Blood Supply. The American Red Cross, Accessed September 11, 2021.
  2. Hasan Arif S, et al. Study of hemolysis during storage of blood in the blood bank of a tertiary health care centre. IJHBT. 2017;33(4), 598-602.
  3. Rapido, F. The potential adverse effects of haemolysis. Blood Transfus. 2017;15(3), 218-221.
  4. Recipient Epidemiology and Donor Evaluation (REDS) Program. National Heart, Lung, and Blood Institute, Accessed September 11, 2021.
  5. Recipient Epidemiology and Donor Evaluation Study III (REDS III) Vein to Vein Databases. National Heart, Lung, and Blood Institute. Accessed September 11, 2021. 
  6. Kleinman S, et al. The National Heart, Lung, and Blood Institute Recipient Epidemiology and Donor Evaluation Study (REDS-III): a research program striving to improve blood donor and transfusion recipient outcomes. Transfusion. 2014; 43(3,2), 942-955.
  7. Lanteri MC, et al. Intradonor reproducibility and changes in hemolytic variables during red blood cell storage: results of recall phase of the REDS-III RBC-Omics study. Transfusion. 2019;59(1), 79-88.
  8. Page GP, et al. Multiple-ancestry genome-wide association study identifies 27 loci associated with measures of hemolysis following blood storage. J Clin Investig. 2021;131(3), e146077.
  9. Kanias T, et al. Ethnicity, sex, and age are determinants of red blood cell storage and stress hemolysis: results of the REDS-III RBC-Omics study. Blood Adv. 2017; 1(15), 1132-1141.
  10. Fang F, et al. Sex hormone intake in female blood donors: impact on haemolysis during cold storage and regulation of erythrocyte calcium influx by progesterone. Blood Transfus. 2019;17(4), 263-273.
  11.  Alexander K, et al. Testosterone replacement therapy in blood donors modulates erythrocyte metabolism and susceptibility to hemolysis in cold storage. Transfusion. 2020; 61, 108-123.

Catherine Crawford-Brown, MSc, MScComm

Catherine Crawford-Brown, MSc, MScComm, is a health science and research writer with a master’s in science communication from Laurentian University. She also has a master’s of science in pathology and molecular medicine from Queen’s University where she worked on developing a liquid biopsy for breast cancer. She was formerly the digital media editor for Lab Manager.