By comparing the expression of tissue specific transcription factors, we were able to show that the isolated NP is relatively free of AF/CEP and marrow cell contamination, but the above‐described method is insufficient to result in an AF/CEP fraction free of NP cell contamination, as shown by the detection of NP‐specific gene (Bra, Cd24) in AF/CEP fractions and the presence of NP remnants in centrifuged IVDs by histology. Here, CD24 is linked to atrial fibrillation.