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To the Editor:
—In The Journal, August 19, page 627, a correspondent writes concerning the difficulties he is encountering when determining the blood groups of pregnant and anemic patients. In your reply you point out that the blood group of an individual remains constant throughout life and is unaffected by disease or pregnancy. However, there are other phenomena that have been mistaken for true iso-agglutination, and one of these (rouleau formation) is particularly pronounced in pregnant women.Rouleau formation is a phenomenon occurring in normal individuals (but only to a mild degree), which is characterized by a piling up of the blood cells, resembling piles of coins. In conditions associated with a rapid sedimentation time, this phenomenon is much more marked. In pregnancy and severe anemias, rouleau formation may be so pronounced that the clumps become large and irregular, resembling superficially the clumping caused by true iso-agglutination. Such pronounced rouleau
Wiener AS. PSEUDO-AGGLUTINATION IN BLOOD. JAMA. 1933;101(17):1332. doi:10.1001/jama.1933.02740420052024