3-stage test that differentiates true pernicious anemia from blind loop syndrome; urinary excretion is measured after each stage. Stage 1Ñradioactive vitamin B12 is given; stage 2 (if there is low urine excretion after stage 1)Ñin low-excretion (< 7%Ð25%), a trial of intrinsic factor is given; stage 3Ñtetracycline is given. (If excretion rises to normal levels, diagnosis is blind loop syndrome.)