Page 72 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

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A bleeding tendency (hemorrhagic diathe- agulopathies (→ D1) can affect practically
sis [HD]) may be caused by disorders of the each of the plasma factors, but deficiency of
coagulation or fibrinolysis system (plasma some of the factors may produce relatively
HD) as well as disorders of TC (thrombocytic few symptoms (e.g., factors of the contact
HD), or of vascular defects (vascular HD). phase, factor XI). The most common (one of
While in plasma disorders minimal mechani- 10 000 newborn boys) of the the X-chromo-
cal injury result in hematomas (bruises) and somal recessive forms is classical hemophilia
bleeding into joints, thrombocytic and vascu- (Type A). This was, for example, inherited
lar HDs are characterized by punctuate, tiny from Queen Victoria by numerous male de-
insect bite–like cutaneous bleedings (pete- scendants of European royal houses (women
chiae; → A, photo). are carriers). The most common bleeding sites
The probable cause of a more serious HD are the muscles and the large joints of the leg,
can be elucidated with a few simple clotting the latter becoming markedly deformed with
tests (→ B). In the Quick test, plasma is tran- time (hemophilic arthropathy). Hemophilia A
siently made incoagulable with substances is due to the absence, reduced formation, or
that form complexes with Ca 2+ (citrate, oxa- defect of factor VIII. The fivefold rarer hemo-
late, or EDTA); an excessive amount of Ca 2+ philia B (factor IX deficiency) is similar in its
and tissue thrombokinase are then added and mode of inheritance and symptoms to hemo-
the resulting clotting time is compared with philia A. The rare homozygous hereditary defi-
serial dilutions of normal plasma. If, for exam- ciency of factor I (afibrinogenemia), of factor II
Blood ple, the test plasma coagulates after the same (hypoprothrombinaemia), of factors V, VII, and
X leads especially to marked bleeding after se-
time interval as 1:1 diluted normal plasma,
3 the Quick value is 50% (normal range: 70– vere injury or operations. Homozygous defi-
125%). Low Quick values denote that either ciency of α 2 -antiplasmin, an important inhibi-
factor VII (exogenous system) or the cascade tor of fibrinolysis (→ D3) also results in a he-
initiated by factor X is abnormal or is influ- mophilia-like bleeding tendency. Factor XIII
enced by vitamin K antagonists (→ B,C,D). To deficiency is characterized by fibrin instability
measure partial thromboplastin time (PTT), so that bleedings occur only after a long inter-
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kephalin, kaolin (substitute for contact activa- val (up to 1 ⁄2 days). The routine clotting tests
tion), and Ca 2+ are added to the citrated plas- are usually normal in factor XIII deficiency, be-
ma and the time until clotting (= PTT) is mea- cause actual clotting is unchanged.
sured (normal: 25–38 s). If it is increased, the ! Acquired coagulopathies (→ D2) occur
disorder lies either in the endogenous activa- when formation of the various factors is re-
tion or in the common final pathway from fac- duced, when they are inhibited (e.g., by ad-
tor X onward (→ B, C). To measure (plasma) ministration of heparin [→ E] or by immune
thrombin time, thrombin is added to the cit- coagulopathies, e.g., factor VIII antibodies), or
rated plasma and the clotting time determined if their consumption is high (consumption
(normal: 18–22 s); the result can reveal fibrin- coagulopathy). As most of the clotting factors
ogen deficiency (→ B), or can be used to moni- are formed in the liver, liver damage (in partic-
tor treatment with heparin, which enhances ular liver cirrhosis; → p.172ff.) results in clot-
the inhibitory action of antithrombin III on ting disorders. Simultaneously occurring por-
thrombin (→ E). An abnormality in the plate- tal hypertension further increases the risk of
lets usually goes hand in hand with prolonged hemorrhages (mainly from esophageal vari-
bleeding time (bleeding > 5 min after, e.g., a ces; → p.170ff.) because platelets are seques-
prick into the ear lobe). A TC deficiency tered in the enlarged spleen, resulting in
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(thrombocytopathy; < 50 × 10 /µL blood) can thrombocytopenia (see below). As several
be distinguished from an abnormality of plate- clotting factors are vitamin K–dependent (see
let function (thrombocytopathy) by means of a above), a coagulopathy can also be caused by
platelet count (→ C). deficiency or inhibition of vitamin K (→ D2).
Plasma hemorrhagic diathesis (coagulo- Causes of vitamin K deficiency are:
62 pathies) are caused by congenital or acquired – obstructive jaundice, in which fat-soluble
clotting factor deficiency. The hereditary co- vitamins (e.g., vitamin K 1 from green plants
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Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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