Extravascular

ex·tra·vas·cu·lar (kstr-vsky-lr)

adj.

1. Located or occurring outside a blood or lymph vessel.

2. Lacking vessels; nonvascular.

---

extravascular

situated or occurring outside a vessel or the vessels.

---

hemoglobinuria

Hematology The presence of Hb in the urine which, if of sufficient quantity, colors urine, the intensity of which directly correlates with the quantity of Hb. See Paroxysmal cold hemoglobinuria, Paroxysmal nocturnal hemoglobinuria.

hemolysis Destruction or lysis of RBCs

Hemolysis

Intracorpuscular hemolysis

•  Membrane defects, eg hereditary elliptocytosis, spherocytosis, stomatocytosis and paroxysmal nocturnal hemoglobinuria

•  Metabolic defects, eg G6PD, pyruvate kinase deficiency

•  Abnormal Hbs see Hemoglobin

Extracorpuscular hemolysis

1º immune reactions, eg autoimmune hemolytic anemia

2º immune reactions, due to

• Infections, eg Bartonella, Clostridia, malaria, sepsis

• Neoplasia, eg lymphoma, leukemias

• Drug reactions due to the 'Innocent bystander' phenomenon (drug-antibody complex activates complement, causing intravascular hemolysis, eg quinidine), hapten-mediated —a protein-bound drug attaches to the red cell membrane, eliciting an immune response when the hapten-protein complex is recognized as foreign, evoking an immune response, eg penicillin acting as a hapten

• Induction of autoimmunity by RBC antigen alterations, eg Rh antigen

Physical, eg thermal, concentrated glycerol due to inadequate washing of frozen blood, bladder irrigation, cardiac valves

Extravascular Less severe, IgG-mediated and does not activate complement, eg Rh, Kell, Duffy Laboratory ↓ haptoglobin, ↓ T_1/2 of circulating RBCs, ↑ indirect BR as liver capacity to conjugate BR–ergo direct BR is overwhelmed by massive hemolysis, ↑ LDH, Hb in blood and urine, hemosiderinuria, MetHb and metalbumin, ↑ urobilinogen in urine and feces, ↑ in acid phosphatase, K+, and prostatic acid phosphatase Clin Chem 1992; 38:575; peripheral smears demonstrate anisocytosis, polychromatophilia, nucleated RBCs, basophilic stippling; immune hemolysis is suggested by spherocytes NEJM 2000; 342:722cpc

Intravascular More severe, IgM-mediated and requires complement activation, eg ABO blood groups Laboratory ↑ free Hb  Note: Clinically significant hemolysis is usually detected by hemagglutination, less commonly by hemolysis per se, which detects anti-P,
-P₁, -PP₁Pk, -Jka, -Lea, occasionally also anti-Leb and -Vel