=====Mean Normal Prothrombin Time (MNPT)=====

**Calculation of  Mean Normal Prothrombin Time (MNPT)**

  *Mean Normal Prothrombin Time- It is geometric mean of PT of reference sample group. MNPT is the denominator for calculation of international Normalized Ratio (INR)

  *With each new lot of PT reagent, MNPT is derived for calculation of INR

  *Method for calculation of  MNPT

  -Collect citrated plasma of apparently healthy individuals (20 donors)(i.e. collect blood from 20 healthy individuals in citrate vacutte and centrifuge them at 1500 g for 10 min to obtain platelet poor plasma.
  -Perform PT of each Sample. E.G. the PT value for different sample s X1,X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13, X14, X15, X16, X17, X18, X19, X20
  -Take out geometric mean of these 20values.
  -geometric mean(y)= (X1,X2, X3, X4, X5, X6, X7, X8, X9,…………………………….X20)1/20
  -This geometric mean (y) is Mean Normal Prothrombin Time
  -Any PT Value is reported in the form of INR.
INR= (PT of test/MNPT)ISI           
Where ISI is provided by the company providing the PT reagent
  -To establish the normal reference range of PT, after taking out the arithmetic mean, calculate standard Deviation (SD)


**Reference:**

  -Reference Manual of STA compact (STAGO)
  -Practical hematology (Dacie and Lewis) - Eleventh edition; 2012
  -Reagent insert of STAGO reagent (Neoplastin CI Pl