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Between blessings: If one is between blessings he may answer for all matters.
Short blessing: If one already recited G-d’s name in one of the short, one sentence, blessings, then he may not interrupt the blessing for any matter.
Long blessing: If one is in middle of a long blessing, such as Asher Yatzar or Hamaavir Sheiyna, then if he already recited a few words after “Elokeinu Melech Haolam”, then the law follows the same law as one who is in the midst of Shema. Thus he may interrupt the blessing in order to answer Kaddish, Kedusha or Barchu. If one has already reached G-d’s name in the closing blessing, then he must finish the blessing and may not interrupt. If one stopped to answer directly prior to saying the closing blessing of Baruch, then one needs to repeat a few words prior to saying the closing blessing.
 Ketzos Hashulchan 5/11
 Such as he recited “Asher Yatzar Es Haadam”. This is required as otherwise it is considered as if he is in the middle of a one sentence blessing of which the law is that one may not make an interval. [ibid; Kaf Hachaim; Nishmas Kol Chaiy] Thus if he did not yet say these words he is to say them and then answer.
 Chayeh Adam 5/13; Biur Halacha 66
 As one is required to say a few words of relation to the blessing prior to concluding the blessing. [ibid; M”B 66/52]