Master the board step 3

Master the Boards: USMLE Step 3
After B12 replacement
therapy:
• Reticulocytes improve
first.
• Neurological
abnormalities improve
last.
··
Most accurate tests: Low B12 level (for B12 deficiency) and folate level (for
folate deficiency). Note: Up to 30 percent of those with B12 deficiency can
have a normal B12 level, because transcobalamin is an acute phase reactant
and any form of stress can cause its elevation. If you suspect B12 deficiency
but the B12 level is normal, order a methylmalonic acid level. Homocysteine
levels go up in both vitamin B12 deficiency and folate deficiency.
··
When asked, after finding a low B12 level or elevated methylmalonic acid level,
“What is the next best test to confirm the etiology of the B12 deficiency?”
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