CLINICAL LAB SCIENEC

CHAPTER 13: HEMATOLOGY AND COAGULATION 361
6. Quickly replace the tubes into the heat block for 7 to 8 seconds.
7. Immediately remove the tubes from the heat block. Note the time and gently tilt
the tubes slowly back and forth, observing for the appearance of a fibrin clot
(Figure 13-20). Record the time elapsed.
8. Discard all supplies used for the procedure in the appropriate containers. A disinfectant
should be used to clean the work surfaces and equipment should be
cleaned and restored to its former position. Gloves should be discarded appropriately
and the hands washed thoroughly in accordance with established policies.
Reporting of Results
Report your findings from the Manual Prothrombin Time procedure in the Procedure #8
Report Form or other form supplied by your instructor. Results are reported in seconds.
The prothrombin time is reported as the International Normalized Ratio (INR) value.
Since each lot of reagent (thromboplastin) may have a different sensitivity, each lot of
reagent is assigned an International Sensitivity Index by its manufacturer. There
are several equations that may be used for calculating the INR. For this procedure, calculate
the INR using the equation below, and as demonstrated in Example 13-4.
Calculation
INR
( Measured PT )ISI
Normal PT
Example 13-4
Using the equation above and the following sample values, calculate the INR.
Normal control value
10.2 sec
Prothrombin time for unknown
20.4 sec
ISI 1.2
INR
( 20.4 ) 1.2 2.4
10.2
Fibrin clot
FIGURE 13-20 Manual tilt method for prothrombin time test.
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