Trusted medical expertise in seconds.

Access 1,000+ clinical and preclinical articles. Find answers fast with the high-powered search feature and clinical tools.

Try free for 5 days
Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer.

Basics of hematology

Last updated: July 12, 2021

Summarytoggle arrow icon

Hematology is the study of blood and the disorders related to it. Human blood consists of blood cells and plasma. Blood has many functions, including transporting oxygen and nutrients to tissues, removing waste materials (e.g., carbon dioxide, urea), regulating body temperature, and carrying cells responsible for coagulation and immune response. There are three main types of blood cells, all of which originate from hematopoietic stem cells, which are located primarily in the bone marrow: red blood cells (RBCs; erythrocytes), white blood cells (WBCs; leukocytes), and platelets (thrombocytes). RBCs are hemoglobin-carrying cells that primarily transport oxygen. There are two types of WBCs: granulocytes and lymphocytes. Granulocytes are part of the innate immune system and play a key role in the immune response to bacteria, fungi, and parasites. Lymphocytes include cells that are responsible for both the innate (natural killers) and adaptive (T and B cells) immune system. T and B cells, in contrast to the cells involved in innate immunity, can target specific antigens presented to them by antigen-presenting cells. Platelets, small anucleate cells produced by megakaryocytes, are required for hemostasis.

Functions of blood [1][2]

  • Transport of:
    • Oxygen, nutrients, and hormones to tissues
    • Carbon dioxide to the lungs for elimination
    • Metabolic waste products to kidneys and liver for elimination
  • Protection from pathogens
  • Hemostasis
  • Regulation of body temperature, signal transmission, and acid-base homeostasis

Blood volume

  • On average, blood constitutes ∼ 7% of the total body weight of adults (∼ 70 mL/kg). [1][3]
  • The actual circulating blood volume varies and depends on age, weight, and height.
  • For children ≥ 35 kg, adolescents, and adults, the total blood volume can be estimated using the Nadler equation: [4]
    • Men: BV = (0.3669 × H3) + (0.03219 × W) + 0.6041
    • Women: BV = (0.3561 × H3) + (0.03308 × W) + 0.1833
      • BV: blood volume in liters
      • H: height in meters
      • W: weight in kilograms
  • For neonates, infants, and children up to 14 years, the following estimates can be used: [5]
Blood volume in individuals of different age
Age Estimated blood volume (mL/kg)
0–30 days 80–85
1–12 months 75–80
13–24 months 85
2–3 years 80
4–6 years 76–77
7–14 years 70–75

Blood constituents [1][2][3]

Overview of blood cell types
Cell Characteristics Function
RBC (erythrocyte)

WBC (leukocyte)

Neutrophil
Eosinophil
Basophil
Monocyte
Lymphocyte
Thrombocyte
Blood cells in peripheral tissue
Macrophage
Mast cell
Dendritic cell
Plasma cell

Never Let Monkeys Eat Bananas: Neutrophils > Lymphocytes > Monocytes > Eosinophils > Basophils.

Bone marrow [2][7]

Types of bone marrow
Characteristic Red marrow Yellow marrow
Location
Function
Composition

Stromal cells of the bone marrow [2][7]

Cells of the stromal compartment of bone marrow are not hematopoietic themselves, but they play a critical role in maintaining and regulating hematopoiesis (e.g., by removing potentially harmful cells and substances).

Hematopoiesis (blood cell production) [2]

Growth factors for hematopoiesis [1][2]

Overview of hematopoietic growth factors
Growth factor Produced by Function
Stem cell factor (SCF)

Granulocyte-monocyte colony-stimulating factor (GM-CSF)

Granulocyte colony-stimulating factor (G-CSF)

Macrophage colony-stimulating factor (M-CSF)

Erythropoietin (EPO)
Thrombopoietin (TPO)

RomiPLoSTIM STIMulates PLatelets. SarGRaMoSTIM STIMulates GRanulocytes and Monocytes.

Erythropoiesis (RBC production) [2]

To recall the sequence of prenatal erythropoiesis sites, think Young Livers Synthesize Blood: Yolk sac, Liver, Spleen, Bone marrow.

RBC morphology and physiology

Myelopoiesis [1][2]

Granulocytes [1][2][17][18][19]

Types of granulocytes
Cell Characteristics Function Causes of increase Causes of decrease
Neutrophil granulocyte

Eosinophil granulocyte

Basophil granulocyte

  • Basopenia: difficult to assess because the normal basophil count is already very low

Agranulocytosis

Causes Pretty Major Collapse To Defense Cells”: some drugs that can cause leukopenia Clozapine, Propylthiouracil, Methimazole, Carbamazepine, Ticlopidine, Dapsone, Chloramphenicol.

Monocytes, macrophages, and mast cells [1][2][27]][28]

Characteristics of tissue-residing immune cells
Cell type Characteristics Function Causes of increase Causes of decrease
Monocyte
  • 3–7% of all leukocytes
  • Diameter: ∼ 5–20 μm
  • Remain in the bloodstream for only ∼ 8 hours before migrating to tissue
Macrophage
Mast cell [30]
  • N/A

Lymphopoiesis (lymphocyte production) [2][31]

Lymphocyte physiology

T lymphocytes (T cells)

CD4/CD8 ratio

Natural killer T cells (NKT cells) [32]

B lymphocytes (B cells)

Natural killer cells (NK cells) [2][33][34]

Thrombopoiesis (platelet production) [2]

Platelet physiology

  1. Hall JE. Guyton and Hall Textbook of Medical Physiology. Elsevier ; 2016
  2. Gartner LP. Textbook of Histology. Elsevier ; 2017
  3. Ashton N. Physiology of red and white blood cells. Anaesthesia & Intensive Care Medicine. 2013; 14 (6): p.261-266. doi: 10.1016/j.mpaic.2013.03.001 . | Open in Read by QxMD
  4. Nadler SB, Hidalgo JH, Bloch T. Prediction of blood volume in normal human adults. Surgery. 1962; 51 (2): p.224-32.
  5. Linderkamp O, Versmold HT, Riegel KP, Betke K. Estimation and prediction of blood volume in infants and children. Eur J Pediatr. 1977; 125 (4): p.227-234. doi: 10.1007/bf00493567 . | Open in Read by QxMD
  6. Murke F, Görgens A, Horn P, Giebel B. Dissecting the origin of dendritic cell and macrophage subsets in human hematopoiesis. Exp Hematol. 2017; 53 : p.S76. doi: 10.1016/j.exphem.2017.06.161 . | Open in Read by QxMD
  7. MARGARET H. BARON. Concise Review: Early Embryonic Erythropoiesis: Not so Primitive After All. STEM CELLS. 2013 .
  8. Werner Schmidt, MD, Shaul Yarkoni, MD, Philippe Jeanty, MD, Peter Grannum, MD, John C. Hobbins, MD. Sonographic Measurements of the Fetal Spleen: Clinical Implications. Journal of Ultrasound in Medicine. 1985 .
  9. Francois Forestier, Fernand Daffos, Nicole Catherine, Michele Renard, and Jean-Paul Andreux. Developmental Hematopoiesis in Normal Human Fetal Blood. Blood. 1991 .
  10. Colin A Sieff, MB, BCh. Overview of hematopoietic stem cells. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/overview-of-hematopoietic-stem-cells.Last updated: November 20, 2018. Accessed: May 31, 2019.
  11. Rich RR, Fleisher TA, Shearer WT et al. Clinical Immunology: Principles and Practice. Elsevier ; 2012
  12. Riley LK, Rupert J. Evaluation of Patients with Leukocytosis.. Am Fam Physician. 2015; 92 (11): p.1004-11.
  13. Mak TW, Saunders ME. The Immune Response - Basic and Clinical Principles. Elsevier ; 2006
  14. Doan T, Melvold R, Viselli S, Waltenbaugh C. Immunology. Lippincott Williams & Wilkins ; 2012
  15. Levinson W. Review of Medical Microbiology and Immunology. Lange ; 2012
  16. Chen Q, Ye W, Jian Tan W, et al. Delineation of Natural Killer Cell Differentiation from Myeloid Progenitors in Human. Scientific Reports. 2015; 5 (1). doi: 10.1038/srep15118 . | Open in Read by QxMD
  17. Ramaiah L, Bounous DI, Elmore SA. Hematopoietic System. Elsevier ; 2013 : p. 1863-1933
  18. Sabatine MS. Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine. Lippincott Williams & Wilkins ; 2013
  19. Khurana I. Medical Physiology for Undergraduate Students. Elsevier Health Sciences ; 2014
  20. Granulocytes: Causes of High & Low Levels + Normal Range. https://selfhacked.com/blog/granulocytes/. Updated: May 30, 2019. Accessed: June 3, 2019.
  21. Johnston A, Uetrecht J. Current understanding of the mechanisms of idiosyncratic drug-induced agranulocytosis.. Expert Opin Drug Metab Toxicol. 2015; 11 (2): p.243-57. doi: 10.1517/17425255.2015.985649 . | Open in Read by QxMD
  22. Kaufman DW, Kelly JP, Jurgelon JM, et al. Drugs in the aetiology of agranulocytosis and aplastic anaemia.. Eur J Haematol Suppl. 1996; 60 : p.23-30. doi: 10.1111/j.1600-0609.1996.tb01641.x . | Open in Read by QxMD
  23. Andrès E, Mourot-Cottet R, Maloisel F, et al. Idiosyncratic drug-induced neutropenia & agranulocytosis. QJM. 2017 : p.hcw220. doi: 10.1093/qjmed/hcw220 . | Open in Read by QxMD
  24. Neupogen (Filgrastim) FDA Label.
  25. Lamberti JS, Bellnier TJ, Schwarzkopf SB, Schneider E. Filgrastim treatment of three patients with clozapine-induced agranulocytosis.. J Clin Psychiatry. 1995; 56 (6): p.256-9.
  26. Birmingham A, Mancuso C, Williams C. Use of granulocyte colony-stimulating factor in the treatment of methimazole-induced agranulocytosis: a case report. Clinical Case Reports. 2017; 5 (10): p.1701-1705. doi: 10.1002/ccr3.1124 . | Open in Read by QxMD
  27. Khurana I. Textbook of Human Physiology for Dental Students. Elsevier Health Sciences ; 2014
  28. Pal GK, Pravati GK. Textbook Of Practical Physiology - 2nd Edn.. Orient Blackswan ; 2006
  29. Sheikh Z, Brooks P, Barzilay O, Fine N, Glogauer M. Macrophages, Foreign Body Giant Cells and Their Response to Implantable Biomaterials. Materials. 2015; 8 (9): p.5671-5701. doi: 10.3390/ma8095269 . | Open in Read by QxMD
  30. Krystel-Whittemore M, Dileepan KN, Wood JG. Mast cell: A multi-functional master cell. Front Immunol. 2016; 6 : p.620. doi: 10.3389/fimmu.2015.00620 . | Open in Read by QxMD
  31. Travlos GS. Normal Structure, Function, and Histology of the Bone Marrow. Toxicol Pathol. 2006; 34 (5): p.548-565. doi: 10.1080/01926230600939856 . | Open in Read by QxMD
  32. Inês Alvarez-Martins, Leonor Remédio, Inês Matias, Lucília N. Diogo, Emília C. Monteiro, and Sérgio. The impact of chronic intermittent hypoxia on hematopoiesis and the bone marrow microenvironment. Pflügers Archiv: European Journal of Physiology. 2016 .
  33. All you need to know about bone marrow. https://www.medicalnewstoday.com/articles/285666.php. Updated: December 15, 2017. Accessed: June 6, 2019.
  34. Sidney LE, Branch MJ, Dunphy SE, Dua HS, Hopkinson A. Concise Review: Evidence for CD34 as a Common Marker for Diverse Progenitors. Stem Cells. 2014; 32 (6): p.1380-1389. doi: 10.1002/stem.1661 . | Open in Read by QxMD
  35. Leila N. Varghese, Jean-Philippe Defour, Christian Pecquet, and Stefan N. Constantinescu. The Thrombopoietin Receptor: Structural Basis of Traffic and Activation by Ligand, Mutations, Agonists, and Mutated Calreticulin. Frontiers in Endocrinology. 2017 .
  36. Khurana. Textbook Of Medical Physiology. Elsevier India ; 2005
  37. UpToDate. Major medications with a definite association with agranulocytosis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. http://www.uptodate.com/contents/image?imageKey=HEME%2F65507&topicKey=HEME%2F8374&rank=1~150&source=see_link&search=agranulocytosis&utdPopup=true.Last updated: January 1, 2017. Accessed: May 7, 2017.
  38. Quinto et al. Relationship between haemoglobin and haematocrit in the definition of anaemia. Tropical Medicine and International Health. 2006; 11 (8): p.1295-1302. doi: 10.1111/j.1365-3156.2006.01679.x . | Open in Read by QxMD
  39. Craig D. McClain, Michael L. McManus. A Practice of Anesthesia for Infants and Children. Elsevier Health Sciences ; 2009 : p. 159-175
  40. Absolute vs. corrected reticulocyte count. https://www.pathologystudent.com/absolute-vs-corrected-reticulocyte-count/. Updated: May 6, 2015. Accessed: June 3, 2019.
  41. LABORATORY VALUES.
  42. Kovalszki A, Weller PF. Eosinophilia. Primary Care. 2016; 43 (4): p.607-617. doi: 10.1016/j.pop.2016.07.010 . | Open in Read by QxMD
  43. Christopher Spry. Eosinophilia in Addison's disease.. Yale Journal of Biology and Medicine. 1976 .
  44. Faramarz Naeim, P. Nagesh Rao, Sophie Song, Ryan T. Phan. Atlas of Hematopathology. Elsevier Science Publishing ; 2018 : p. 871-884
  45. Mathias Hensel,a Lena Grädel, MD, Alexander Kutz, MD, Sebastian Haubitz, MD, Andreas Huber, MD, Beat Mueller, MD, Philipp Schuetz, MD, MPH, and Thomas Hügle, MD, PhD. Peripheral monocytosis as a predictive factor for adverse outcome in the emergency department. Medicine. 2017 .
  46. L Saeed, M M Patnaik, K H Begna, A Al-Kali, M R Litzow, C A Hanson, R P Ketterling, L F Porrata, A Pardanani, N Gangat, and A Tefferi. Prognostic relevance of lymphocytopenia, monocytopenia and lymphocyte-to-monocyte ratio in primary myelodysplastic syndromes: a single center experience in 889 patients. Blood Cancer Journal. 2017 .
  47. Maria Carolina Costa Melo Svidnicki, Fernando Ferreira Costa, and Sara Teresinha Olalla Saad. Screening of Mutations Related to Hereditary Anemias Using NGS-Targeted Sequencing Panel. Blood. 2017 .
  48. Robert T. Means Jr. Pure red cell aplasia. Blood. 2017 .
  49. Le T, Hwang W, Muralidhar V, White JA. First Aid for the Basic Sciences: Organ Systems, Third Edition. McGraw Hill Professional ; 2017
  50. Ginhoux F, Guilliams M. Tissue-Resident Macrophage Ontogeny and Homeostasis. Immunity. 2016; 44 (3): p.439-449. doi: 10.1016/j.immuni.2016.02.024 . | Open in Read by QxMD