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Diagnostic Tests: Schilling Test
Overview — Clinical Conditions for Which the Schilling Test Is Used
The Schilling test is a historical diagnostic test used to determine the cause of vitamin B₁₂ (cobalamin) deficiency.
Although rarely used today, it is a classic board-style question.
The most common cause of B₁₂ deficiency is pernicious anemia, which results from autoantibodies against intrinsic factor (IF) or against parietal cells that produce IF.
The Schilling test helps differentiate:
How the Schilling Test Is Performed
The Schilling test is performed in stages:
Stage 1
Stage 2
The test is repeated, this time with oral intrinsic factor added to the radiolabeled B₁₂.
Interpretation:
Schilling’s test is rarely the correct answer today, but in board-style questions you choose it when:
In other words, use the Schilling test only when the cause of B₁₂ deficiency is unknown and pernicious anemia has not been confirmed by simpler tests.
If you’d like, I can provide a comparison of B₁₂ deficiency vs. folate deficiency, or a simple diagnostic algorithm for evaluating macrocytic anemia.
Overview — Clinical Conditions for Which the Schilling Test Is Used
The Schilling test is a historical diagnostic test used to determine the cause of vitamin B₁₂ (cobalamin) deficiency.
Although rarely used today, it is a classic board-style question.
The most common cause of B₁₂ deficiency is pernicious anemia, which results from autoantibodies against intrinsic factor (IF) or against parietal cells that produce IF.
The Schilling test helps differentiate:
- Pernicious anemia (intrinsic factor deficiency)
from - Intestinal malabsorption of B₁₂
- Other causes of poor cobalamin absorption
How the Schilling Test Is Performed
The Schilling test is performed in stages:
Stage 1
- Oral dose of radiolabeled vitamin B₁₂ (cyanocobalamin) is given.
- Intramuscular injection of unlabeled B₁₂ is given 1 hour later to saturate binding sites and ensure radiolabeled B₁₂ is excreted in the urine if absorbed normally.
- Urine is collected for 24 hours to measure the percentage of radiolabeled B₁₂ excreted.
- Low urinary excretion → indicates poor absorption of B₁₂
Stage 2
The test is repeated, this time with oral intrinsic factor added to the radiolabeled B₁₂.
Interpretation:
- Urinary excretion normalizes → Pernicious anemia (lack of intrinsic factor).
- Urinary excretion remains low → intestinal malabsorption (e.g., ileal disease, bacterial overgrowth, pancreatic insufficiency).
Schilling’s test is rarely the correct answer today, but in board-style questions you choose it when:
- The patient clearly has vitamin B₁₂ deficiency, and
- Tests for intrinsic factor antibodies and parietal cell antibodies are negative, and
- The etiology is still unclear, or
- The antibody tests are not available among the answer choices
In other words, use the Schilling test only when the cause of B₁₂ deficiency is unknown and pernicious anemia has not been confirmed by simpler tests.
If you’d like, I can provide a comparison of B₁₂ deficiency vs. folate deficiency, or a simple diagnostic algorithm for evaluating macrocytic anemia.
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