Triple test consists of alpha feto protein (AFP), unconjugated estriol (uE3) and Human chorionic gonadotropin (B-HCG). Inhibin A is now added to the triple test to become Quadruple test
Inhibin A is produced in pregnancy from the placenta. It plateaus during weeks 14-30 weeks. Inhibin A levels are not influenced by maternal age
Measurement of inhibin A is only of value after 14 weeks of gestation, best between 16-18 weeks
Clinical significance
Down syndrome associated with increased inhibin A (bout 2 folds) , increased B-HCG , decreased alpha-feto protein and decreased uE3. Inhibin A increases detection of Down�s syndrome by 10% (from 65% to 75%), with false positive rate of about 5%
Neural tube defects: associated with increased AFP, normal HCG , normal uE3 and normal Inhibin A
Trisomy 18 : associated with decreased AFP; Decreased HCG, and decreased uE3 and decreased inhibin A. It detects 92% of cases of this chromosomal anomaly
Turner syndrome: is associated with increased inhibin A in cases with hydrops , but decreased in cases without hydrops. It generally detects 53% of Turner cases
In summary: Quadruple test can be of value in increasing sensitivity and specificity of detecting chromosomal anomalies in fetuses in pregnancy
.Dr. Hussam Abu- Farsakh, M.D
American boards of Anatomic, Clinical Pathology and Cytopathology