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!
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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.
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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?
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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.
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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.
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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).
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In any event, the take home message is:
DO NOT DISCOUNT B12 DEFICIENCY BECAUSE THE SERUM B12 LEVEL IS NORMAL!!!
You are an astronaut on board a spaceship. Your task is to study the effects of spaceflight on the hematological system. You draw blood from your fellow astronauts into EDTA-containing tubes. There is no centrifuge on board, so you store the blood at 4C until landing.
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The problem is that water enters RBCs over time, so the RBCs swell and the MCV increases artificially. Since RBC number does not change, the Hct becomes falsely elevated (Hct = RBC count x MCV). Water movement inside the cell dilutes the Hb, resulting in decreased MCHC.
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When you get back to earth, you wish to determine the effect of spaceflight on the MCV. How do you correct for the effect of water shifts?
You measure the MCH and compare it to baseline. The weight in Hb - thus, the MCH - does not change with storage.
Did you know that HEYDE SYNDROME, which today is defined by a triad of 1) aortic stenosis, 2) recurrent bleeding from GI angiodysplasia, and 3) acquired type IIA von Willebrand syndrome was first described by Edward Heyde in a 1958 correspondence to the NEJM?
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... and that he described the association of calcific aortic stenosis and massive GI bleeding (not angiodysplasia per se, and certainly not with any understanding of pathogenesis).
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MECHANSISM
The current leading hypothesis explaining the pathophysiology of Heyde’s syndrome is acquired von Willebrand syndrome (AVWS):
56 yo F with essential thrombocythemia (PLT > million/ul) found to have hyperkalemia (K+ 6.5 mEq) in the outpatient clinic. She is asymptomatic. What is the next test you would order?
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You order a whole blood potassium level (though a plasma potassium would have sufficed). Whole blood K+ is 4.7 mEq.
What is the diagnosis?
3/8
The diagnosis is pseudohyperkalemia.
DEFINITION: marked elevation of serum potassium levels (>0.4 meq/L [mmol/L]) as compared to the normal plasma potassium concentration in the absence of clinical evidence of electrolyte imbalance.
Did you know that red blood cells are only found in vertebrates and that they are nucleated in all classes (fish, amphibians, reptiles, birds) except mammals?
It is safe to say that the loss of the erythrocyte nucleus in the ancestral mammal provided a survival advantage.
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Otherwise the anomaly would have been quickly filtered (snuffed) out by natural selection.
One way of explaining this remarkable evolutionary event is through the lens of trade-offs.
1. What's the upside of losing your RBC nucleus?
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1a. Anucleate RBCs (aRBCs) are more deformable, and can squeeze through small capillaries, increasing the surface area in contact with endothelium (hence O2 diffusion).
1b. aRBCs have less intrinsic viscosity, reducing peripheral resistance and increasing cardiac output.
Hematologists use Hct as a surrogate for blood viscosity (in polycythemia) and as a (less than optimal) surrogate for oxygen carrying capacity (in anemia).
Gastroenterologists and intensivists also use Hct as a marker of intravascular volume status in critical care.
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This is especially true in patients with acute pancreatitis:
1. Hct is incorporated into severity scores, including APACHE II and the Ranson score.
1a. In APACHE II, the higher the Hct (above 46%), the higher the score and the worse the prognosis.
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1b. In the original Ranson score, a big drop in Hct at 48 h predicted a poor outcome. In a revised Ranson score, this has been flipped around so that failure of Hct to drop is a bad sign (makes more sense as it is in line with continued hemoconcentration).