This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Which of the following methods can be used to detect rubella infection in children - 
Select and explain. 
A. T4 cell count, B. Fetal hemoglobin, C. IgM antibody in fetal blood, D. IgA Antibody in fetal blood
C: IgM antibody in fetal blood
Answer: C: IgM antibody in fetal blood 
Explanation: Ans. is 'c' i.e., IgM antibody in fetal blood Laboratory diagnosis o Isolation of virus in cell cultures of throat samples, urine or other secretions. o Normally, maternal rubella antibodies in the form of IgG is transferred to infants and is gradually last over a period of 6 months. Persistent beyond 1 year in an unvaccinated child suggests the diagnosis of congenital rubella. o Presence of Ig M antibodies is diagnostic. o PCR for rubella RNA.