When Should Kids Be Tested for Antithrombin Deficiency?

If you have congenital antithrombin deficiency, it is completely natural to worry about passing this condition to your children. The short answer to your question is: yes, your children can inherit the condition, but most medical experts recommend waiting until they are older before testing them for it ^[1][2]. Unless your child is having major surgery, needs hormonal birth control, or shows unusual symptoms, testing is usually delayed until adolescence or young adulthood ^[3][4].

Understanding the Odds: How It Is Inherited

Congenital antithrombin deficiency is an autosomal dominant genetic condition ^[1]. In plain language, this means that a child only needs to inherit one copy of the mutated gene (usually the SERPINC1 gene) from one parent to have the deficiency ^[5][6]. Because you have the condition, each of your children has exactly a 50% chance of inheriting the gene mutation ^[5].

Why Doctors Usually Recommend Waiting

While hearing that your child has a 50% chance of inheriting a clotting disorder is frightening, it is important to know that the baseline risk of a blood clot in childhood is incredibly small. Even with the deficiency mathematically increasing that risk compared to the general population, the overall chance of a clot in an active, healthy child remains very low ^[7]. Current medical guidelines generally discourage routine testing for asymptomatic children (children with no symptoms of a clot) ^[8][9].

Doctors recommend delaying testing for several important reasons:

• It does not change daily care: Even if a child tests positive, doctors will not put a healthy, growing child on daily blood thinners just to prevent a clot ^[2][10]. Since knowing the test result does not change how you raise or treat your child day-to-day, early testing is not medically necessary ^[2].
• Children’s blood is different: Initial testing usually involves a simple blood test to check antithrombin activity levels rather than a complex DNA test. However, newborns and infants naturally have lower antithrombin levels than adults, which usually reach adult ranges by around 6 months of age ^[11][12]. This can lead to confusing or false-positive results if the blood tests are done too early or not interpreted carefully ^[1].
• Emotional and practical impacts: Testing a young child can cause unnecessary medical anxiety for both you and your child. Furthermore, placing a genetic diagnosis on a minor’s permanent medical record could potentially create complications for them later in life when they apply for certain types of insurance, such as life or disability coverage.

When Your Child Should Be Tested

While routine testing is delayed, there are specific, high-risk situations where knowing your child’s antithrombin status becomes medically important. You should discuss testing with your child’s pediatrician if:

• They need major surgery or are immobilized: Surgery significantly increases the risk of blood clots. Preoperative testing is essential before major procedures (like orthopedic or heart surgeries) so the medical team can provide preventative blood thinners or antithrombin concentrate if needed ^[3][13]. Severe sports injuries that require casting or prolonged bed rest should also trigger a conversation about testing ^[14].
• They are approaching adolescence: Testing is highly recommended for teenagers who are considering starting hormonal therapy, such as estrogen-based birth control pills ^[4][15]. Estrogen increases clotting risk, so teens with antithrombin deficiency will need non-hormonal or progestin-only alternatives. This is also a critical time to warn teenagers about the extreme dangers of smoking and vaping, which heavily compound the risk of blood clots ^[4]. Testing is also vital before a young adult plans a pregnancy ^[16][4].
• They develop suspicious symptoms: If your child ever experiences unexplained swelling in an arm or leg, sudden chest pain, or shortness of breath—which are signs of a blood clot (thrombosis)—they should be evaluated and tested immediately ^[14].
• They have other medical conditions: If your child develops conditions that increase clotting risk, such as severe kidney issues (nephrotic syndrome) or autoimmune diseases, testing may be warranted earlier ^[17][18].

For now, the most empowering thing you can do is keep your child active, ensure they stay hydrated, and simply inform their doctors, dentists, or physical therapists that there is a strong family history of congenital antithrombin deficiency.

What to say to your child’s doctor:
“I have congenital antithrombin deficiency, which is an inherited clotting disorder. I know standard protocol is to delay testing children until they are older or need surgery, but I want to make sure this family history is clearly noted in their chart just in case of an emergency.”