Behaviour of the protein C (PC)/protein S (PS) ratio in patients with thrombosis

Abstract number: P0023

Blanco^* A., Gennari† L. C., Nadal† M. V., Domínguez‡ M. P., Meschengieser† S., Lazzari† M. A.

†Inst Invest Haematol Acad Nac de Medicina, Argentina; ^*Inst Invest Haematol, Acad Nac de Medicina, Argentina; ‡Inst Invet Haematol Acad Nac de Medicina, Argentina

Recently, it has been reported that the PCactivity/PStotal antigen ratio seems to be more accurate to identify carriers of a PC gene mutation than the measurement of PC levels, since normal PC values could be observed in carriers of a PC gene mutation. We analysed the behaviour of different ratios (R): PCactivity/PSactivity (R1), PCactivity/PSfree (R2), PCactivity/PStotal (R3) and also PCactivity in patients with arterial (A = 40) or venous (V = 98) thrombosis (T) and in control group (C = 40). PC activity (ILTestTM Protein C), PS activity (ILTestTM Protein S), PS free and total antigen (Laurell's assay) were performed.

Results  

An inverse relationship was not found between PC values and any of the PS tests (P Spearman's test > 0.05). However, a correlation (P < 0.001) between PCactivity and R1, R2 or R3 was found, in both, C and T groups. Cut-off values (mean controls ± 2SD) were estimated for each R. We found not significant (P Yates' corrected Chi square > 0.1) differences in the prevalence of abnormal PCactivity, R1, R2 or R3 between A (PC 2.5%; R1 15%; R2 7.5%; R3 7.5%) and V (PC 7.1%; R1 12.2%; R2 10.2%; R3 10.2%) groups. The percentage of abnormal PC values in T (5.8%) group was not significantly (P > 0.1) higher than in C (0%). However, an abnormal R1 value was more prevalent (P = 0.027) in T (13.0%) than in C (0%) and also, abnormal values of R2 or R3 appeared to be more prevalent in T (R2 and R3: 9.4%) than in C (R2 and R3: 0%) groups, but the differences did not reach statistical significance (pR2 and pR3 = 0.076). Our preliminary data showed that there are patients with normal PC values and abnormal R in both A (R1: 5/40, R2 and R3: 2/40) and V (R1: 5/98, R2 and R3: 3/98) groups.

Conclusion  

According to the results reported by Libourel et al. Patients with abnormal R could be carriers of a PC gene mutation and should be investigated in order to exclude it. If we apply only the criterion of low PC, we could be missing a number of patients with PC mutations and this could be important if the thrombotic risk depends on the mutation rather than on the PC level. However, we found that the percentage of abnormal R, mainly R1, is quite similar in A and V groups, in contrast to the higher prevalence of PC defects reported in venous thrombosis. Large series of patients should be studied in order to verify the utility of the Rs to identify not only PC mutations carriers but also individuals at thrombotic risk.