Here's a cool case with an important take-home message.
A 48 yo M is referred to you with macrocytic anemia. Before looking at the graphic you should have a rough differential diagnosis at your finger tips!
2/9
Peripheral smear shows large RBCs, anisocytosis but otherwise unremarkable.
You work up the patient for macrocytic anemia by checking B12/folate and copper levels, liver function, thyroid function, SPEP but you stop short of a bone marrow biopsy. See graphic for results.
3/9
All lab tests are negative with the exception of a (VERY) elevated LDH, an increased AST:ALT ratio and low haptoglobin. A CT abdomen was normal (as was the PT/INR and serum albumin).
What is this suggestive of?
4/9
The results are suggestive of hemolysis.
Yet, the retics are low.
... and the LDH is disproportionately high.
High suspicion for ineffective erythropoiesis secondary to B12 deficiency!
5/9
OK, now a little Hx and Px 😉:
On Hx, the patient complained of fatigue and shortness of breath on exertion. There was no past history of abdominal surgery. He was not a vegetarian. Px exam revealed glossitis. CNS status was normal.
6/9
Serum B12 levels are NOT 100% sensitive for diagnosing B12 deficiency. If clinical suspicion is high, the next step is to check for functional B12 deficiency by measuring serum MMA and HCY (per BSH guidelines [and common sense]).
7/9
The MMA (more specific than HCY) was astronomically high, clinching the diagnosis of functional B12 deficiency. Anti-intrinsic factor antibodies were positive, c/w a diagnosis of pernicious anemia. The patient received B12 therapy and his labs values normalized.
8/9
It is not clear why some patients with functional/cellular B12 deficiency have normal serum B12 levels.
In most cases, it is likely related to increased binding of B12 to haptocorrin at the expense of transcobalamin II (the functional B12 transport protein).
9/9
In any event, the take home message is:
DO NOT DISCOUNT B12 DEFICIENCY BECAUSE THE SERUM B12 LEVEL IS NORMAL!!!
In acute GI bleed anemia, would you give 1 g IV iron regardless of ferritin?
Results:
• 27% yes — anticipate iron debt
• 12% sometimes
• 21% only if ferritin is low
• 41% no
2/13
First, an important acknowledgment:
There is no right answer here.
There are no firm guidelines that tell us what to do in this situation. Reasonable clinicians land in different places.
This is a gray zone where physiology, timing, and judgment matter.
3/13
So rather than argue what we should do, I want to walk through the numbers and biology and explain why some clinicians anticipate iron debt even when ferritin is normal.
Yesterday I posted a CBC + reticulocyte count and asked for your diagnostic thoughts. Many of you offered great reasoning. The correct diagnosis was hemoglobin C disease.
Let’s unpack why this case is such a good learning example. 👇
2/9
Microcytosis often triggers a reflex binary:
iron deficiency vs thalassemia trait.
That’s a useful starting point. But it’s incomplete. Structural hemoglobin variants (like HbC and HbE) also belong on that list.
3/9
Several people calculated the Mentzer index (MCV/RBC):
75 / 4.0 ≈ 18 → “suggests iron deficiency (ID).”
Important teaching point:
The Mentzer index was designed to distinguish thal trait vs ID. It is not validated for structural hemoglobinopathies like HbC or HbE.
Patients with SLE can present with a staggering array of hematologic abnormalities. Virtually no component of the blood is spared. Everything is fair game: