Diagnosis – The diagnosis of SIBO is established with a positive carbohydrate breath test or duodenal aspirate culture. We perform a carbohydrate breath test to diagnose SIBO as it is simple, non-invasive, and widely available. The lactulose/glucose breath test is diagnostic of SIBO if there is an absolute increase in hydrogen by ≥20 ppm above baseline within 90 minutes. A methane level ≥10 ppm, regardless of the time during the breath test, can identify intestinal methanogen overgrowth (associated with a constipation phenotype). A bacterial concentration of >10³ colony-forming units/mL of duodenal aspirate is diagnostic of SIBO. However, the test requires an upper endoscopy to obtain an aspirate and the results are poorly reproducible. (See 'Diagnosis' above.)

uptodate에서는 schilling test 얘기가 없네요. breath test와 culture 밖에 없어요

Schilling test는 검사 과정에서 특정 방사성 동위원소를 이용해야 하는데, 생산이 거의 중단되어서 검사도 거의 진행하지 않는다네요. 구닥다리 검사 느낌인 것 같아요.

게다가 예전에는 비타민 B12 주사 치료가 고가였어서 비타민 B12 부족의 원인 감별을 위한 검사가 중요했는데, 요즘은 비타민 B12 치료가 다양해지고 가격도 싸져서 원인 감별을 빡세게 해야 할 필요가 줄어든 것도 한 몫 하는 것 같아요.

(출처 Wikipedia : Many labs have stopped performing the Schilling test, due to lack of production of the cobalt radioisotopes and labeled-B₁₂ test substances. Also, injection replacement of B₁₂ has become relatively inexpensive, and can be self-administered by patients, as well as megadose oral B₁₂. Since these are the same treatments which would be administered for most causes of B₁₂ malabsorption even if the exact cause were identified, the diagnostic test may be omitted without damage to the patient (so long as follow-up treatment and occasional serum B₁₂ testing is not allowed to lapse).