The blood clotting system in humans is highly regulated to maintain a delicate balance between controlling bleeding in response to injury, but avoiding clot formation within blood vessels (thrombosis). This is achieved by the presence of many different proteins, some of which help the blood to clot (procoagulant) while others prevent it (anticoagulant). Both protein C & S are anticoagulant proteins and any deficiency of these proteins, either hereditary or acquired, is associated with a predisposition to clot formation within veins where the flow of blood is slower (compared to the rapid flow seen in arteries).
A large number of individuals with hereditary protein C deficiency are asymptomatic and often a family history is important to assess the association of deficiency and the risk of thrombosis. The condition may also be transiently acquired secondary to liver disease, acute inflammatory states, sepsis, administration of some drugs, etc.
The laboratory diagnosis requires a decreased protein C activity level. Each laboratory has to establish its own biological reference interval by testing the pooled plasma from 20 non-pregnant non-clotting persons not taking medications known to affect the protein C level. The normal functional (clot-based) levels are 60-130 per cent of normal while immunological assay levels range from 70 to 130 per cent. If a tested blood sample reveals a low value, it should be repeated on a fresh specimen to confirm the finding. Similarly, protein S deficiency may be hereditary or acquired, the latter usually due to liver diseases or vitamin K deficiency. Diagnosing protein S deficiency requires the estimation of both free and total antigen levels along with a functional assay. All three tests are required since several variants of this deficiency are known.
A combined deficiency of both protein C and S, though not unknown, is rare and there have been only a few reports of such families. Other tests like a plasma-based test for APC resistance, a genetic test for factor V Leiden and prothrombin G20210A, tests for plasminogen and dysfibrinogenemia also need to be done in the evaluation of a thrombophilic patient. You need to discuss all these issues with your doctor as recurrent abortion is not the uusal presentation of thrombophilias.
There is a clinical state called antiphospholipid syndrome that is characterised by recurrent venous or arterial thrombosis (blood clot within the arteries or veins) and/or recurrent abortions (in women) associated with typical laboratory abnormalities. The abnormal tests include persistently raised levels of different types of antibodies directed against phospholipids (e.g. anticardiolipin antibody and antibeta-2 glycoprotein) or abnormal clotting tests which confirm the presence of a circulating anticoagulant. You should be investigated for this.