Various tools have been developed to identify whether a sample is "corrected" or "not corrected" by adding pooled normal plasma. One tool is the Rosner Index.
The Rosner Index subtracts the clotting time of the pooled normal plasma (PNP) from the clotting time of the 1:1 mix. This result is then divided by the clotting time of the patient sample. The equation is as follows:
Rosner Index = (1:1 mix clotting time result - PNP clotting time result) / initial prolonged clotting time of patient sample x 100
Or, written in abbreviated terms:
With this method:
- High index value represents the possibility of an inhibitor
- Low index value would represent a possible factor deficiency
For example, an index of 10 or lower indicates correction, while 15 and above suggests no correction. If a value of 10–15 is obtained after the calculation, it is recommended that your test be repeated.Each laboratory must determine its reference interval for the Rosner Index.
