Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (290 page)

   Bone marrow aspirate (indicated in very selected cases) may reveal marked red cell hyperplasia and megaloblastic maturation in both vitamin B
₁₂
and folate deficiencies. Otherwise, it may uncover other reasons for macrocytosis, such as myelodysplastic syndrome MDS.

   Serum LDH and indirect bilirubin are elevated in folate and vitamin B
₁₂
deficiency.

   Limitations

   In the presence of coexisting iron deficiency, MCV may not be elevated, even in cases of overt folate or cobalamin deficiency.

   Low cobalamin levels develop during pregnancy.

   One hospital meal may normalize serum folate level (but not RBC).

Methylmalonic acid increases in renal insufficiency.

MICROCYTIC ANEMIAS

   Definition

Anemias characterized by low MCV (<82 fL) and hypochromia. Most common: iron deficiency anemia, to be differentiated from the thalassemias and occasionally from anemia of chronic diseases. Despite the high frequency of iron deficiency anemia, patients should not be treated automatically with iron without determining the cause of the anemia.

   Who Should Be Suspected?

Suspect iron deficiency if the following are present:

   History of GI, vaginal, or massive, repeated urinary bleeding

   Microcytosis, hypochromic

   Poor diet

   Laboratory Findings

   First line of investigation: serum ferritin has a specificity of 98% but a sensitivity of only 25% for a 12 μg/L threshold. Because ferritin is an acute-phase reactant, it may be normal or even increased despite iron deficiency when the patients have serious medical problems, such as chronic inflammatory conditions and active liver disease. As a consequence, a normal ferritin value does not exclude iron deficiency. Very low values are definitely diagnostic, iron deficiency is confirmed, and there is no need to obtain serum iron and total iron-binding capacity (TIBC). Investigation of etiology (history, stool examination for occult blood, GI investigation, pelvic and rectal examinations) is mandatory.