Inhibin A Test

Your doctor will order inhibin A test as a part of the quadruple test in the second trimester of your pregnancy. This is a screening test that checks the amount of inhibin A in a pregnant woman to determine if her baby has any birth defects or genetic abnormalities such as Down syndrome.

Pregnant women who have a family history of birth defects, are above 35 years of age or are diabetic and are taking insulin are at a higher risk of having a baby with birth defects.

If your foetus has birth defects, your inhibin A levels would be twice as high compared to that in a healthy pregnancy.

Fasting is not required before this test. Your doctor will explain if you need special instructions for the test or if you have to stop taking certain medications.

This test is performed by drawing blood from the arm. The following procedure is used to collect the sample:

• A laboratory technician will tie a tourniquet (a tight band) around your upper arm and ask you to tighten your fist. This will help to make your veins more prominent so a blood sample can be withdrawn with ease.
• He/she will use an antiseptic solution to clean a site on your lower arm and will insert a sterile needle into a vein to collect a small amount of blood. You may feel a slight pricking sensation when the needle is inserted. 
• Once enough sample is drawn, the technician will release the tourniquet and put pressure on the site to stop bleeding.

After the procedure, you may notice mild bruising at the site - it will fade in a few days. If you are scared of needles, please inform your doctor or nurse so that they can help you feel at ease.

Normal results: 

The normal reference range of inhibin A is as below:

• Early to late follicular phase of the menstrual cycle: 1.8-90.3 pg/mL
• Mid-cycle (day 0): 16.9-91.8 pg/mL
• Early to late luteal phase of the menstrual cycle: 16.1-97.5 pg/mL[8]
• Between 15-19 weeks of pregnancy: 41.4-690 pg/mL
• Between 21-25 weeks of pregnancy: 47.6-1719 pg/mL
• Postpartum: <2-42 pg/mL[9]
• After menopause: <6.9 pg/mL
• In normal males: <2.1 pg/mL

Abnormal results:

Increased values of inhibin A may be due to conditions such as:

• Down syndrome
• Preeclampsia
• Some types of cancer

Low levels of inhibin A may be due to conditions such as:

• Premature or physiologic ovarian failure
• Menopause

The results of these tests, along with other factors such as women’s age, helps the doctor determining the diagnosis.

If the results are positive, then the doctor may order further tests like amniocentesis (a process in which the amniotic fluid sample is collected and tested for foetal defects) to confirm the diagnosis.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.