Diagnosis and Management of Pernicious Anemia

Initial Laboratory Assessment

The American Gastroenterological Association recommends a complete blood count (CBC) with red cell indices to identify macrocytic anemia, which is characteristic of vitamin B12 deficiency, with a mean corpuscular volume (MCV) >100 fL 1, 2
Reticulocyte count should be measured to assess bone marrow response, typically low or normal in pernicious anemia 2
Iron studies, including serum ferritin and transferrin saturation, should be performed to rule out concurrent iron deficiency 1

Serum vitamin B12 level measurement is the first-line test, with levels <200 pg/mL strongly suggesting deficiency, according to the American College of Physicians 2
Methylmalonic acid (MMA) and homocysteine levels should be measured, as they are more sensitive markers of functional B12 deficiency and may be elevated even when serum B12 levels are in the low-normal range 3, 2
Holotranscobalamin (holoTC) measurement, if available, has greater sensitivity than serum cobalamin for detecting B12 deficiency, as recommended by the National Institute of Nutrition 3

Neurological symptoms may precede hematological abnormalities in about one-third of cases, so absence of anemia does not rule out B12 deficiency, according to the Nutrition Research Reviews 3

Renal impairment significantly elevates homocysteine independent of vitamin status, so interpretation requires assessment of serum creatinine, as noted by the European Heart Journal 4, 5
Moderate homocysteinemia can result from poor diet, mild B12/folate/B6 deficiency, hypothyroidism, impaired renal function, or certain medications, according to the European Heart Journal 4, 5
Intermediate homocysteinemia usually indicates moderate/severe cobalamin or folate deficiency or renal failure, as reported by the European Heart Journal 5, 6

Severe B12 deficiency with markedly elevated homocysteine creates a prothrombotic state that can lead to venous thromboembolism, including pulmonary embolism and potentially fatal complications, as noted by the European Heart Journal 6

A complete blood count (CBC) with mean corpuscular volume (MCV) >100 fL, reticulocyte count, and peripheral blood smear for hypersegmented neutrophils should be performed, as recommended by the Annals of Oncology 7