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USMLE Step 1Haematology and oncologyEP 04 of 14

Intravascular vs extravascular haemolysis: site and labs

Both kinds of haemolysis destroy red cells too early. The site of destruction, and what haptoglobin, LDH, bilirubin and urine show, tells them apart.

  • 5:27 video
  • 3 min read
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  • Published 15 Nov 2026
Video lesson · 5:27 · Watch on YouTubeSeries: Hematology: Anemia, Coagulation & Oncology Basics · @medservatory
Chapters (12)
By the end of this lesson

Distinguish intravascular from extravascular haemolysis by the site of red cell destruction and by haptoglobin, LDH, bilirubin and urine findings.

The short version

  1. Extravascular haemolysis means macrophages in the spleen and liver remove abnormal cells, with jaundice, an often enlarged spleen and usually no haemoglobin in the urine.
  2. Intravascular haemolysis means cells burst in the vessels, so haptoglobin is used up, free haemoglobin reaches the urine and LDH is often several times the upper limit.
  3. Haemolysis means red cells die before their normal span of about 120 days; anaemia, a high reticulocyte count, raised LDH and raised indirect bilirubin point to it.
  4. Haptoglobin can be low in both types, so a low haptoglobin alone does not give the site.
  5. Many diseases do both, but the dominant site sets the pattern.

Intravascular vs extravascular haemolysis: two patients, one question

Two patients are destroying their red cells too fast. One is jaundiced, with a spleen you can feel, but her urine is clear. The other has red-brown urine and no palpable spleen.

The question is where those cells are dying. Intravascular vs extravascular haemolysis is decided by the site of destruction, and the site shows up in four places: haptoglobin, LDH, bilirubin and the urine.

How a normal red cell is removed, and what haemolysis means

A red cell lives about 120 days. Normally, ageing cells are eaten by macrophages in the spleen, liver and bone marrow.[4][1]

Inside the macrophage, haem is split. The iron is recycled, and the rest becomes bilirubin, which travels on albumin to the liver.[4][1]

Haemolysis means red cells die early, before their normal span of about 120 days.[1]

Anaemia, a high reticulocyte count, a raised LDH and a raised indirect bilirubin point to haemolysis. These signs do not say where the cells are dying.[1][3][2]

Extravascular haemolysis: macrophages in the spleen and liver

In extravascular haemolysis, abnormal or antibody-coated cells are removed by macrophages in the spleen and liver. Think of spherocytes, as in hereditary spherocytosis or warm autoimmune haemolytic anaemia.[1][3][2]

Haemoglobin is broken down inside the macrophage, so little reaches the plasma. The result is mostly bilirubin.[1][2]

  • Unconjugated hyperbilirubinaemia and jaundice
  • Extra urobilinogen in the urine
  • Sometimes gallstones
  • A busy, often enlarged spleen
  • LDH only slightly raised
  • Usually no haemoglobin in the urine[1][2]

Intravascular haemolysis: lysis in the vessels

In intravascular haemolysis, cells burst inside the vessels. Causes include shear from a mechanical valve or microangiopathy, complement, malaria, clostridial toxins and a mismatched transfusion.[1][3]

  1. Free haemoglobin spills into the plasmaHaptoglobin binds it, so haptoglobin is used up and falls.[1][3][2]
  2. Free haemoglobin exceeds haptoglobinThe kidney filters it. This is haemoglobinuria: red-brown urine with no red cells on microscopy.[1][2]
  3. Tubular cells absorb someThey store the iron as haemosiderin, which later appears in the urine.[1][3]

LDH is often several times the upper limit, and bilirubin rises less.[2][3]

Extravascular and intravascular haemolysis side by side

Intravascular vs extravascular haemolysis
FeatureExtravascularIntravascular
Where cells dieMacrophages in the spleen and liverInside the vessels
ExamplesHereditary spherocytosis, warm autoimmune haemolytic anaemiaParoxysmal nocturnal haemoglobinuria, mechanical valve shear
BilirubinRaised unconjugated bilirubin, jaundiceRises less
LDHOnly slightly raisedOften several times the upper limit
HaptoglobinCan be lowUsed up and falls
UrineUsually no haemoglobin; extra urobilinogenHaemoglobinuria, later haemosiderin

Many diseases do both, but the dominant site sets the pattern.[3][1]

The haptoglobin trap

Haptoglobin can be low in both types of haemolysis, so a low haptoglobin alone does not give the site.[2][1]

Back to the two patients

Reading the two patients
  1. Jaundice, a big spleen and clear urine: macrophage clearance, so extravascular, perhaps hereditary spherocytosis.
  2. Red-brown urine, an undetectable haptoglobin and a very high LDH: lysis in the vessels, so intravascular, perhaps paroxysmal nocturnal haemoglobinuria.[2][1]

Practice question

Original · USMLE style
Your turnQB-MS-S1-HEME-003-01

A 64-year-old man with a mechanical aortic valve has had 3 weeks of fatigue and breathlessness. Haemoglobin is 8.6 g/dL and the reticulocyte count is 7%. Serum lactate dehydrogenase (LDH) is 1150 U/L (reference range 140 to 280 U/L). Haptoglobin is undetectable. The peripheral smear shows schistocytes.

Which of the following best describes the site of red cell destruction and the urine findings expected in this patient?
Pick one option. Your answers stay on this device.

Common questions

What is the difference between intravascular and extravascular haemolysis?

In extravascular haemolysis macrophages in the spleen and liver remove abnormal or antibody-coated red cells. In intravascular haemolysis cells burst inside the vessels and free haemoglobin spills into the plasma.

Which labs separate intravascular from extravascular haemolysis?

Intravascular haemolysis uses up haptoglobin, puts haemoglobin and later haemosiderin in the urine, and often raises LDH several times above the upper limit. Extravascular haemolysis mainly raises unconjugated bilirubin, raises LDH only slightly, and usually leaves no haemoglobin in the urine.

Does a low haptoglobin mean intravascular haemolysis?

No. Haptoglobin can be low in both types, so a low value alone does not give the site. The urine and the LDH help decide.

What is haemoglobinuria in haemolysis?

It is red-brown urine with no red cells on microscopy. It appears when free haemoglobin exceeds haptoglobin and the kidney filters it.

Can haemolysis be both intravascular and extravascular?

Yes. Many diseases do both, but the dominant site sets the pattern.

Transcript

Read the full narration, by chapter645 words

0:00Two patients, one question

Two patients are destroying their red cells too fast. One is jaundiced, with a spleen you can feel, but her urine is clear. The other has red-brown urine and no palpable spleen. Where are those cells dying, and what do the labs show? Today: tell intravascular from extravascular

0:16Today's table: the labs that tell them apart

haemolysis by the site of destruction, and by haptoglobin, LDH, bilirubin and urine. A red cell lives about 120

0:26How a normal red cell is removed

days. Normally, ageing cells are eaten by macrophages in the spleen, liver and marrow. Inside the macrophage, haem is split: the iron is recycled, and the rest becomes bilirubin, which travels on albumin to the liver.

0:44What haemolysis means and the shared signs

Haemolysis just means red cells die early, before their normal span of about 120 days. Anaemia, a high reticulocyte count, a raised LDH and raised indirect bilirubin point to haemolysis. The next question is where. In extravascular haemolysis,

1:02Extravascular haemolysis: macrophages, spleen, liver

abnormal or antibody-coated cells are removed by macrophages in the spleen and liver. Think of spherocytes, as in hereditary spherocytosis or warm autoimmune haemolytic anaemia. Haemoglobin is broken down inside the macrophage, so little reaches the plasma. The result is mostly bilirubin: unconjugated hyperbilirubinaemia, jaundice, extra urobilinogen in the urine, and sometimes gallstones. The spleen is busy and often enlarged, LDH is only slightly raised, and the urine usually holds no haemoglobin.

1:42Intravascular haemolysis: lysis in the vessels

In intravascular haemolysis, cells burst inside the vessels. The causes are physical or immune: shear from a mechanical valve or microangiopathy, complement, malaria, clostridial toxins, or a mismatched transfusion. Free haemoglobin spills into the plasma, where haptoglobin binds it, so haptoglobin is used up and falls. When free haemoglobin exceeds haptoglobin, the kidney filters it: haemoglobinuria, red-brown urine with no red cells on microscopy. Tubular cells absorb some and store the iron as haemosiderin, which later appears in the urine. LDH is often several times the upper limit, and bilirubin rises less.

2:28The haptoglobin trap

One trap: haptoglobin can be low in both types, so a low haptoglobin alone does not give the site. Many diseases do both, but the dominant site sets the pattern.

2:40Back to our two patients

Back to our patients. The jaundiced woman with the big spleen and clear urine is extravascular, perhaps hereditary spherocytosis. The other, with red-brown urine, an undetectable haptoglobin and a very high LDH, is intravascular, perhaps paroxysmal nocturnal haemoglobinuria.

3:00Practice question

Your turn. A 64-year-old man with a mechanical aortic valve has had three weeks of fatigue and breathlessness. Haemoglobin is 8.6 g/dL, and reticulocytes are 7%. LDH is 1150 units per litre, with a reference range of 140 to 280. Haptoglobin is undetectable, and the smear shows schistocytes. Which of the following best describes the site of red cell destruction and the urine findings expected? A, splenic macrophages; no haemoglobin in the urine. B, splenic macrophages; haemoglobin and haemosiderin in the urine. C, hepatic macrophages; no haemoglobin in the urine. D, within the circulation; no haemoglobin or haemosiderin in the urine. E, within the circulation; haemoglobin and haemosiderin in the urine. Pause here and decide. A is out: splenic macrophages clear damaged cells, but shear from a valve breaks them in the circulation. B is out: the site is wrong again, and urine haemoglobin follows free haemoglobin, not splenic clearance. C is out: the liver is another extravascular site, with the same mismatch. D is out: the site is right, but undetectable haptoglobin means free haemoglobin overwhelmed it and reached the urine. So the answer is E.

4:35Answer and explanation

Shear lyses cells in the circulation; free haemoglobin uses up haptoglobin, passes the kidney, and appears as haemoglobin, then haemosiderin, in the urine.

4:49Recap

Three things to keep. One: extravascular means macrophages in the spleen and liver, with jaundice, splenomegaly and no urine haemoglobin. Two: intravascular means lysis in the vessels, with a used-up haptoglobin, haemoglobinuria, haemosiderinuria and a very high LDH. Three: haptoglobin can fall in both, so let the urine and the LDH decide.

5:16Next: G6PD deficiency vs hereditary spherocytosis

Next, two classic haemolytic diseases: G6PD deficiency and hereditary spherocytosis.

Sources

Numbers in the text, e.g. [1], point here
  1. Overview of Hemolytic Anemia. MSD Manual Professional Version. msdmanuals.com/professional/hematology-and-oncology/anemias-caused-by-hemolysis/overview-of-hemolytic-anemia
  2. Barcellini W, Fattizzo B. Clinical applications of hemolytic markers in the differential diagnosis and management of hemolytic anemia. Dis Markers. 2015. europepmc.org/article/PMC/PMC4706896
  3. Haemolytic anaemia. Life in the Fast Lane (LITFL). litfl.com/haemolytic-anaemia/
  4. Erythrocytes. OpenStax Anatomy and Physiology 2e, section 18.3. openstax.org/books/anatomy-and-physiology-2e/pages/18-3-erythrocytes

The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.

Image credits. Illustrations: Servier Medical Art (smart.servier.com), CC BY 4.0, adapted (recoloured, outlined, resized): erythrocyte (isotonic, very hypotonic and protein-erythrocyte versions), spleen, liver, gallbladder, capillary, kidney, urine test, heart valve surgery. Macrophage icon by Servier (via bioicons.com), CC BY 3.0, https://creativecommons.org/licenses/by/3.0/. Bone marrow icon by El-Jayawant (via bioicons.com), CC BY 4.0. All other drawings are original.

Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-HEME-003.

For exam study only, not medical advice. Read the medical disclaimer.

In this series

Playlist on YouTube
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  1. EP 01Microcytic anaemia: four causes, four iron fingerprints5:37
  2. EP 02Hepcidin: why iron falls in inflammation5:34
  3. EP 03B12 vs folate deficiency: MMA, homocysteine and the nerves5:23
  4. EP 04Intravascular vs extravascular haemolysis: site and labs5:27
  5. EP 05G6PD deficiency vs hereditary spherocytosis, by mechanism5:36
  6. EP 06Sickle cell disease pathophysiology: HbS to vaso-occlusion5:26
  7. EP 07Primary haemostasis: platelet adhesion, activation and aggregation5:53
  8. EP 08Coagulation cascade: PT vs aPTT, pathway by pathway5:21
  9. EP 09Von Willebrand disease vs haemophilia: the labs that separate them5:32
  10. EP 10Anticoagulants: target, monitoring test and reversal agent5:34
  11. EP 11Heparin-induced thrombocytopenia: why a low count clots5:29
  12. EP 12DIC vs TTP vs HUS: mechanism and the PT/PTT5:33
  13. EP 13AML vs ALL vs CML vs CLL: leukemia classification made simple5:44
  14. EP 14Oncogenes vs tumour suppressor genes: one hit or two5:17