What are the investigations needed for proper assessment of coagulation?

Identifiy the proper screening tests of coagulation

Platelet count:

Performed routinely on almost all patients using particle counters as part of routine complete blood picture.

Interpretation:

Normal range: 150,000 and 450,000 per mm³ of blood (150-450 x 10⁹/L)

When beeding disorders are associated with either thrombocytopenia or thrombocytosis, evaluation of bone marrow is required .

Bleeding time: Bleeding Time, Duke; Bleeding Time,

• Measure platelet function.
• It is neither a sensitive nor a specific test.

Methodology: puncture the patient's middle finger using a lancet, and every 30 seconds gently blots the blood with filter paper to see if the bleeding has stopped.

Interpretation:

• Normal range : The expected normal range is 1-4 minutes
• prolonged in:

1. low platelet counts

2. Platelet function disorders ( hereditary e.g von Willebrand disease ),( acquired eg uremia, macroglobulinemia, and a variety of other conditions, asprine intake ).

Prothrombin time :

The Prothrombin Time or PT is a screening test which measures the activity of the factors of the extrinsic and common pathways including factors II, V, VII, X, and fibrinogen.

Indication:

1- To detect coagulation disorders of the extrinsic pathway factors.

2- Monitor oral anticoagulant therapy such as warfarin.

Warfarin is

• A drug used in management of thrombosis.
• It inhibits the synthesis of the vitamin K dependent factors, factors II, VII, IX and X by blocking the regeneration of vitamin K and shows a dose dependent effect.

Principle:

The PT test is performed by adding tissue thromboplastin and calcium to plasma and measuring the time for clot formation.

It can be performed either manually by tilt tube method or by an automated method, (fibrometer or a photo-optical instrument).

Interpretation

• Normal range:The expected normal range for a PT is 10-14 seconds depending on the type of reagent used.

The International Normalized Ratio or INR was developed for the purpose of standardizing the monitoring of warfarin therapy due to variation in the composition and responsiveness of PT reagents.

INR = [patient's results/normal patient average]^(ISI)

• Prolongation of the PT can be caused by:

1- factor VII deficiency due to liver disease (The PT is more sensitive than the APTT for liver disease)or increased consumption in disseminated intravascular coagulation

2- Deficiencies in vitamin K, which can be caused by anticoagulants (warfarin), malabsorption or lack of intestinal colonization by bacteria (such as in newborns)..

3- The PT is less sensitive than the PTT to the presence of heparin or a lupus-like inhibitor. In addition, poor factor synthesis (may prolong the PT.

Improper sample collection or processing can result in shortening or prolongation of the PT.

Activated partial thromboplastin time (aPTT)

aPTT is an assay used to screen for abnormalities of the intrinsic clotting system. It is also used to monitor the anticoagulant effect of circulating heparin.

Indication:

1-To detect coagulation disorders of intrinsic pathway.

2- Monitor the circulating anticoagulant therapy (heparin).

Principle:

aPTT assay is performed by adding a factor XII activator platelet substitutes phospholipid., and calcium ions.

Interpretation

• Normal range :The expected normal range for a aPTT is 35.0-42.0 seconds

• Shortening of the PTT has little clinical relevance.
• prolonged in the

1- presence of a factor deficiency,

2- factor inhibitor, heparin or lupus-like inhibitors.

To distinguish the above causes, mixing studies are performed, in which the patient's plasma is mixed (initially at a 50:50 dilution) with normal plasma.

abnormality does not corrected, the sample is said to contain an "inhibitor" (either heparin, antiphospholipid antibodies or coagulation factor specific inhibitors),

while if it does correct a factor deficiency is more likely. Deficiencies of factors VIII, IX, XI and XII and rarely von Willebrand factor (if causing a low factor VIII level) may lead to a prolonged aPTT correcting on mixing studies.

Heparin : is a commercial product

• which is prepared from beef lung or porcine intestinal mucosa
• Administered via intravenous or subcutaneous injection.
• Heparin with its plasma co-factor Antithrombin III inhibits coagulation immediately after being administered.
• It is the drug of choice for treating venous thrombosis by preventing fibrin formation.

The aPTT, although useful in monitoring high level heparin therapy, has had variable effectiveness in monitoring low dose heparin therapy and low molecular weight forms of heparin.

Thrombin time :

Indication:

To screen for abnormalities in the conversion of fibrinogen to fibrin.

Principle:

Addition of thrombin to plasma convert fibrinogen to fibrin

Interpretation:

Normal range:

13-15 second , patient prothrombin time should be within 2 seconds of the control.

  prolonged in:

1-fibrinogen deficiency ( quantitative or qualitative )

2-Heparin

3-Fibrin degradation product.

4-paraprotienaemia.

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