Laboratory investigations to diagnose megaloblastic anemia

Screening tests

Specific diagnostic tests

Schillings test

This test is used to evaluate the absorption of vitamin B12 in the GIT
Test is performed in two parts
- Part I –
  - 0.5 to 1μg of radiolabeled vitamin B12 is administered orally
  - After 2 hours 1000μg of unlabeled vitamin B12 is given as an intramuscular dose
  - This intramuscul;ar dose of vitamin B12 saturates the vit B12 binding sites of transcobalamin I and II and displaces any bound radiolabeled vitamin B 12
  - This causes the urinary excretion of absorbed radiolabeled vitamin B12
  - Radioactivity is measured as in subsequently collected 24hour urine sample and is expressed as percentage of ttotal oral dose
  - In normal individuals, more than 7% of the oral dose of vitamin B12 is excreted in urine
  - If excretion is less than 7%, it indicates impaired absorption which may be due to either malabsorption or lack of intrinsic factor
  - If the part I result is abnormal then part II test is conducted
- Part II
  - patient is given radiolabeled vitamin B12 along with intrinsic factor orally
  - After 2 hours 1000μg of unlabeled vitamin B12 is given as an intramuscular dose
  - If excretion becomes normal, then the cause is lack of intrinsic factor
  - If excretion is below normal, it indicates malabsorption in small intestine
Interpretation of Schillings test
- Part I normal – Dietary deiciency
- Part I abnormal, Part II normal – Pernicious anemia and gastrectomy
- Part I abnormal, Part II abnormal – Malabsorption in small intestine
Disadvantages of test
- This test is time taking and complicated
- Procuring radiolabeled vitamin B12 is difficult
- Collection of urine and renal functions also affect the test results

References

Elaine M. Keohane, Larry J. Smith, Jeanine M. Walenga. Rodak’s Hematology: Clinical principles and application. Fifth edition 2016
Shirish M Kawthalkar. Essentials of Hematology. First edition, 2006.

Laboratory investigations to diagnose megaloblastic anemia

Screening tests

Specific diagnostic tests

Schillings test

This test is used to evaluate the absorption of vitamin B12 in the GIT

Test is performed in two parts

Part I –

0.5 to 1μg of radiolabeled vitamin B12 is administered orally

After 2 hours 1000μg of unlabeled vitamin B12 is given as an intramuscular dose

This intramuscul;ar dose of vitamin B12 saturates the vit B12 binding sites of transcobalamin I and II and displaces any bound radiolabeled vitamin B 12

This causes the urinary excretion of absorbed radiolabeled vitamin B12

Radioactivity is measured as in subsequently collected 24hour urine sample and is expressed as percentage of ttotal oral dose

In normal individuals, more than 7% of the oral dose of vitamin B12 is excreted in urine

If excretion is less than 7%, it indicates impaired absorption which may be due to either malabsorption or lack of intrinsic factor

If the part I result is abnormal then part II test is conducted

Part II

patient is given radiolabeled vitamin B12 along with intrinsic factor orally

After 2 hours 1000μg of unlabeled vitamin B12 is given as an intramuscular dose

If excretion becomes normal, then the cause is lack of intrinsic factor

If excretion is below normal, it indicates malabsorption in small intestine

Interpretation of Schillings test

Part I normal – Dietary deiciency

Part I abnormal, Part II normal – Pernicious anemia and gastrectomy

Part I abnormal, Part II abnormal – Malabsorption in small intestine

Disadvantages of test

This test is time taking and complicated

Procuring radiolabeled vitamin B12 is difficult

Collection of urine and renal functions also affect the test results

References

Elaine M. Keohane, Larry J. Smith, Jeanine M. Walenga. Rodak’s Hematology: Clinical principles and application. Fifth edition 2016

Shirish M Kawthalkar. Essentials of Hematology. First edition, 2006.