Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Blood
Your blood is made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.
Red blood cells (RBC) deliver oxygen from your lungs to your tissues and organs. White blood cells (WBC) fight infection and are part of your immune system. Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer.
There are four blood types: A, B, AB, or O. Also, blood is either Rh-positive or Rh-negative. So if you have type A blood, it's either A positive or A negative. Which type you are is important if you need a blood transfusion. And your Rh factor could be important if you become pregnant - an incompatibility between your type and the baby's could create problems.
Blood tests such as blood count tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working. Problems with your blood may include bleeding disorders, excessive clotting and platelet disorders. If you lose too much blood, you may need a transfusion.
It sits within Blood, Heart and Circulation.
The lead U.S. institute for this subject is the National Heart, Lung, and Blood Institute.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Blood
33,439 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- Targeted Therapy Directed by Genetic Testing in Treating Patients With Advanced Refractory Solid Tumors, Lymphomas, or Multiple Myeloma (The MATCH Screening Trial)National Cancer Institute (NCI)
- Pre-transplant Purging and Post-transplant MRD-guided Maintenance Therapy With Elranatamab in Patients With High-risk Multiple MyelomaM.D. Anderson Cancer Center
- A Phase 1 Study of UB-VV500 With Rapamycin in Relapsed/Refractory Multiple MyelomaUmoja Biopharma
- Brain Blood Flow and Cerebral Autoregulation Monitoring in Critically Ill ChildrenUniversity of Wisconsin, Madison
- Blood Pressure Response to Exercise and Aortic Stiffness in Patients With Cardiovascular-Kidney-Metabolic SyndromeKaramanoğlu Mehmetbey University
- Long-term Follow-up of Long-acting Cabotegravir (CAB LA) for PrEP (Pre-exposure Prophylaxis) in Participants at Risk of Acquiring HIV (Human Immunodeficiency Virus)ViiV Healthcare
Research already completed
- Tumor-Derived FGF19University of Central Florida
- A Study to Investigate the Efficacy and Safety of Baxdrostat in Participants With Uncontrolled Hypertension on Two or More Medications Including Participants With Resistant HypertensionAstraZeneca
- Increasing PrEP Use in High-Risk Social Networks of African-American MSM in Underserved Low-Risk CitiesMedical College of Wisconsin
- NK White Blood Cells and Interleukin in Children and Young Adults With Advanced Solid TumorsNational Cancer Institute (NCI)
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Start Here
- Blood BasicsAmerican Society of Hematology
- Blood Donation FAQsAmerica's Blood Centers
- Blood TestsNational Heart, Lung, and Blood Institute
Diagnosis and Tests
- What You Need to Know About Blood TestingNational Library of Medicine
Related Issues
- Cord Blood Testing and BankingNational Library of Medicine
- Diversity in Blood TypesAmerican Red Cross
Clinical Trials
- ClinicalTrials.gov: Blood CellsNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Blood. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Blood, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.