| Subject | Contents |
| Definition | A blood test that measures the amount of protein S. Deficiencies may lead to the formation of blood clots in arteries or veins. |
| Alternative Names | |
| How the test is performed | Adult or child: Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding . Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test | Adults: Fasting or other special preparation is not necessary. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:infant test or procedure preparation (birth to 1 year) toddler test or procedure preparation (1 to 3 years) preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| How the test will feel | When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed | Protein C and protein S are involved in regulation of coagulation (blood clotting); they inactivate factors V and VIII. |
| Normal Values | Normal values are 66% to 112% inhibition. |
| What abnormal results mean | Deficient protein S can result in excessive clotting tendencies. These are usually vein clots, such as deep vein thrombosis (DVT), but occasionally this disorder can be associated with arterial clots. Deficiency may be inherited or acquired due to other conditions. This can be due to oral contraceptive use or pregnancy, and diseases such as disseminated intravascular coagulation and HIV infection may also be associated with decreased levels of this protein. |
| What the risks are | excessive bleedingfainting or feeling light-headed hematoma (blood accumulating under the skin) infection (a slight risk any time the skin is broken) multiple punctures to locate veins |
| Special considerations | Protein C and Protein S are decreased by Vitamin K antagonist oral anticoagulants (Coumadin, warfarin). Measurements of Protein C or S may be difficult to interpret in patients taking oral anticoagulants During an acute thrombotic episode, Proteins C and S are reduced even if decreased C or S is not the cause of the thrombosis, and measurements of Protein C or S may be misleading until the acute episode is resolved. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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