Q. why dec MCV & inc MCHC in hereditary spherocytosis? - USMLE Forums
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Old 09-06-2016
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Default Q. why dec MCV & inc MCHC in hereditary spherocytosis?

Why decreased MCV and increased MCHC in hereditary spherocytosis?Can anyone shed light on this.
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Old 09-07-2016
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Normal RBC is biconcave. RBCs in heriditary spherocytosis is spherical.
Basic geometry: The shape with the smallest volume that can be occupied by a mass is a sphere.
In hereditary spherocytosis, small bits of membrane are lost and the RBCs form a spherical shape and hence the volume is reduced i.e MCV is reduced. Now this is just for the spherocytes. In heriditary spherocytosis there is increased number of reticulocytes which are large in size compared to the mature RBCs. Thus the final number is a normal to low MCV.

MCHC= Hemoglobin/ Hematocrit.
The hemoglobin is slightly reduced. The hematocrit part is a bit complex. Its reduced but is made of spherical cells. The overall effect is a drop in hematocrit more than hemoglobin resulting in a higher MCHC.

Last edited by datson; 09-07-2016 at 06:33 AM.
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Old 09-07-2016
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so lucidly explained. Thanks Datson.

But, Pathoma has kept Hereditary spherocytosis in "Normocytic hemolytic anemia" (referring to having normal MCV) as opposed to MTB (ie. decreased MCV , as mentioned in the question above). May be, in hereditary spheroctytosis, MCV can be Normal or decreased both. If MCV remains normal, then, MCHC will also be normal according to the formula u mentioned, right?
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Old 09-07-2016
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Thanks for bringing up the point. Will make changes to the original reply.
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