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usmleuser007
I knew the disorder and its pathophysiology. But sometimes the answer choices are so wordy or colorful that you still get it wrong....
+24
sunshinesweetheart
I got this one right but now upon review I'm having trouble ruling out hereditary spherocytosis ("abnormal cell morphology") answer choice. It helps that the dark urine is in the mornings, but is it officially ruled out because of her age? like this is obvi an acquired mutation if someone's 33?
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krewfoo99
@sunshinesweetheart Hereditary Spherocytosis is a autosomnal dominant condition. The patient in the question stem has had dark urine since the past 2 months (acute presentation). Since spherocytosis is hereditary, it wont be present as a acute condition
+7
sexymexican888
@sunshinesweetheart Spherocytosis results in extravascular hemolysis (spleen) so no weird colored urine (due to intravascular hemolysis) as is seen in PNH (complement destroy RBCs in blood vessels)
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suckitnbme
It's so obscure of a test that wikipedia only has 4 sentences on it.
+2
pathogen7
FA2020 added the Ham test to PNH I believe!
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pathogen7
Whoops no sorry I am wrong. They did add something called the EMA test to spherocytosis though.
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snripper
Ham test has been replaced by flow cytometry now. So fck off, NBME.
+1
pseudomonalisa
I remember it like this: PNH occurs at night due to mild respiratory acidosis (slower respiratory rate), which activates complement which destroys RBCs. The test is essentially doing the same thing, putting cells into an acidic environment -> dead RBCs.
+7
submitted by โm-ice(370)
This woman has Paroxysmal Nocturnal Hemoglobinuria. This most often presents in a young adult who has episodes of dark urine in the middle of the night or when waking up in the morning. It's caused by complement activity directly against the patient's own RBCs. Certain glycolipids are needed on the RBC surface to prevent attack from complement, the most notable of which are CD55 and CD59. Patients with PNH have a somatic mutation in which they lost function of a PIGA enzyme needed for proper presentation and attachment of CD55/CD59 on the RBC surface. Therefore the answer is a defect in a cell membrane anchor protein. Without this, complement attacks RBCs.