Cumulative Sum (Cusum) Charting was introduced in
1960s. Deviation from the largest is plotted in a cumulative
manner so that each point represents the sum of all the
deviations to date from the mean or target value. This
method of plotting exaggerates trends in data and makes
shifts of the mean much more obvious than by other plots.
The rules for using the Cusum system for quality control
are less well defined than for the L-J system.
A well-known method for checking precision in clinical
analysis is duplicate testing. In this process, a few of the
specimens that were measured in an earlier batch, are
rechecked with the next batch control.
¾ These of cumulative reports of a single patient
¾ Clinical correlation: If a physician can not interpret a
report on clinical grounds, a repeat test with a fresh
¾ Red cell indices: If reports are giving erroneous rise
or fall in the red cells indices, this usually points to an
¾ Blood film examination ultimately helps in double
checking the analysis done by the instrument.
The college of American Pathologist first introduced
“proficiency testing” survey program in 1960. In the late
60s, the British Committee for Standards in Hematology,
finallydevelopedtheNationalExternalQualityAssessment
Scheme (NEQAS) for Hematology. Such methods are used
by various laboratories all over the world to keep up with
Modern diagnostic systems depends on a calibration
procedure for accurate performance. Calibrators or testing
standards are commercially prepared products, made by a
direct comparison with a primary international standard.
They are used for accuracy and interlaboratory harmonization
of test results. The calibrator has an assigned value as close to
the true value as can be established.
The WHO (World Health Organization) provides a wide
range of biologically important international reference
standard material. Some examples of these which are
available for use in hematology are:
e. Various coagulation factors.
This is concerned with the pre-analytical parts of the
process that require control, if tests are to be reliable and
effective. This involves following a standard guideline at
various steps of a laboratory analysis.
1. Standard of blood collection tube
3. Identification of sample with special reference to
4. Maintenance of transportation standards
6. Establishing normal reference values, assessment of
the significance of results and taking decisions for
Technical Proficiency has always been the corner stone
of the laboratory, but in recent years with the advent
of sophisticated instruments and automation, quality
control has assumed an even more important role in good
laboratory practice. It is the duty of the laboratory staff to
ensure that the tests, which are carried out, are appropriate
and to provide reliable analytical results.
PLATELETS, COAGULATION AND BLEEDING
DISORDERS: LABORATORY INVESTIGATIONS
Platelet Count—Dealt in Depth Elsewhere
Capillary Fragility Test of Hess
(Rumpel-Leede Sign, Tourniquet Test)
1. Inflate sphygmomanometer cuff around arm at 80 mm
2. Look for petechiae in an area 5 cm in diameter just
3. Under normal circumstances the number of petechiae
should be less than 5, more than 5 indicate a positive
A positive test may be found in reduced capillary
positive in thrombocytopenia when the platelet count is
below approximately 70,000 mm3
1. Increased petechiae formation occurs most commonly
in thrombocytopenia and less commonly in:
(i) thrombasthenia, (ii) vascular purpura, (iii) senile
2. The number and size of petechiae are roughly
proportional to the bleeding tendency and possibly to
the degree of thrombocytopenia. However, the test can
be positive because of capillary fragility in the presence
3. Results will be normal in coagulation disorders and
Laboratory Diagnosis of Vascular Bleeding Disorders
Hess’s test is positive in these
• Hereditary hemorrhagic telangiectasia.
1. Menstruation: Capillary fragility is normally increased
2. Infectious disease: Capillary fragility is increased in
3. Age: Women over 40 years with decreasing estrogen
levels may have a positive test that is not indicative of
4. Readministration: Repetition of test on same arm
within 1 week of the first test may lead to error.
5. Variation: Results may vary because of differences in
texture, thickness, and temperature of the skin.
LABORATORY DIAGNOSIS OF PLATELET
Idiopathic Thrombocytopenic Purpura (ITP)
1. Platelet count is usually 10-50 × 109
Clinical Hematology: Bleeding Disorders 273
2. The blood film shows reduced numbers of platelets,
those present are often large.
3. The bone marrow usually shows increased number of
4. Sensitive tests can demonstrate antiplatelet IgG, either
alone or with complement, on the platelet surface or
in the serum in most patients.
survival. In severe cases, the mean platelet survival
6. Hess’s test may be positive in some cases.
Drug Induced Immune Thrombocytopenia
1. Thrombocytopenia. Platelet count is often <14 × 109
2. Bone marrow may show normal or increased numbers
3. Drug dependent antibodies against platelets may be
demonstrated in sera of some patients.
Drugs usually incriminated are:
Disseminated Intravascular Coagulation (DIC)
1. In acute cases blood may not clot due to gross
3. Fibrinogen screening tests, titers or assays indicate
4. Thrombin time is prolonged.
5. High levels of serum fibrin/fibrinogen degradation
products are found in serum and urine.
6. Prothrombin time and partial thromboplastin time are
7. Factor V and factor VIII activity is diminished.
8. Due to microthrombi causing mechanical hemolytic
anemia, RBCs may show crenation and poikilocytosis.
1. DIC may be caused by entry of procoagulant material
into circulation, for example,
• Premature placental separation
• Widespread mucin secreting adenocarcinoma
• Hemolytic transfusion reaction
2. DIC may also be initiated by extensive endothelial
damage and collagen exposure, for example
• Gram-negative and meningococcal septicemia
• Certain viral infections (purpura fulminans)
3. Massive intravascular platelet aggregation can also
precipitate DIC as occurs in some:
• Bacterial and viral infections
• Immune complexes may have a direct effect on
Platelet reactions in the hemostatic process.
3. Abnormal platelet aggregation studies with ADP,
adrenaline, collagen and ristocetin.
4. Abnormal adhesion studies and nucleotide pool
5. Factor VIII clotting assay (for von-Willebrand’s disease).
Abnormal platelet function should be suspected in cases
where bleeding is prolonged despite a normal platelet
count. Various causes included in this are as follows:
1. Platelet storage pool disease: There is defective release
2. Thrombasthenia (Glanzmann’s disease): There is
failure of primary platelet aggregation.
3. Bernard-Soulier syndrome: Platelets are larger than
normal, lack surface glycoprotein and fail to make
phospholipid available or to adhere to vessel walls.
4. von Willebrand’s disease: There is defective platelet
adhesion as well as coagulation factor VIII deficiency.
1. Aspirin therapy: It may lead to abnormal bleeding time
although purpura is rare. Aspirin leads to impaired
thromboxane-A2 synthesis. So, there is failure of the
release action aggregation with ADP and adrenaline.
2. Hyperglobulinemia: Interferes with platelet adherence,
3. Myeloproliferative disorders: Intrinsic abnormalities of
platelet function may occur in patients with essential
thrombocythemia and other myeloproliferative
The duration of bleeding from a standard puncture wound
of the skin is a measure of the function of platelets as well
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