Various tools have been developed that identify whether a sample is "corrected" or "not corrected" by the addition of 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:
1:1 mix PTT - PNP PTT x 100
patient PTT
With this method, a high index value represents the possibility of an inhibitor. A low index value would represent a possible factor deficiency. For example, an index of 10 or lower indicates correction, 15 and above indicates no correction.
If after the calculation is performed and a value of 10-15 is obtained, it is recommended that your test be repeated.
Each laboratory must determine its own reference interval for the Rosner Index.
