Hereditary spherocytosis (HS) is a congenital hemolytic disorder, wherein a genetic mutation coding for a structural membrane protein phenotype leads to a spherical shaping of erythrocytic cellular morphology. As erythrocytes are sphere-shaped (spherocytosis), rather than the normal biconcave disk-shaped, their morphology interferes with these cells abilities to be flexible during circulation throughout the entirety of the body -  arteries, arterioles, capillaries, venules, veins, and organs. This difference in shape also makes the red blood cells more prone to rupture under osmotic and/or mechanical stress. Cells with these dysfunctional proteins are degraded in the spleen, which leads to a shortage of erythrocytes resulting in hemolytic anemia. HS was first described in 1871, and is the most common cause of inherited hemolysis in populations of northern European descent, with an incidence of 1 in 5000 births. The clinical severity of HS varies from mild (symptom-free carrier), to moderate (anemic, jaundiced, and with splenomegaly), to severe (hemolytic crisis, in-utero hydrops fetalis), because HS is caused by genetic mutations in a multitude of structural membrane proteins and exhibits incomplete penetrance in its expression.Early symptoms include anemia, jaundice, splenomegaly, and fatigue. Acute cases can threaten to cause hypoxia secondary to anemia and acute kernicterus through high blood levels of bilirubin, particularly in newborns. Most cases can be detected soon after birth. Testing for HS is available for the children of affected adults. Occasionally, the disease will go unnoticed until the child is about 4 or 5 years of age.
In HS, the erythrocytes fail to pass through fenestrations, and this is where resident splenic macrophages sample, or "bite," part of the stuck spherocytes plasma membranes. The macrophages recognize that the spherocyte is not normal, and the macrophage is "programmed" to destroy irregularities filtered at the spleen from the blood. The resident splenic macrophages therefore phagocytose the spherocytes, causing extravascular hemolysis. This leads to both splenomegaly and anemia. Should this process continue unchecked chronically, inappropriate regulation of erythropoeisis leads to extramedullary hematopoiesis. Clinical Presentation
HS patients present in a vast array of presentations from being asymptomatic, to the extreme situations of splenic rupture and/or hemolytic crisis, or in-utero demise. Asymptomatic HS (mild): 20-30% of patients. Infantile-Onset HS (moderate): 60-75% of patients. Neonatal or In-Utero Onset HS (severe): <5% of patients.The most common presentation will demonstrate jaundice (due to increased unconjugated bilirubin), anemia (with secondary pallor), and a palpable spleen sometimes with concomitant tenderness (due to splenic congestion and splenomegaly). Its worth noting that a subsection of HS patients will also have incidental black pigmented gallstones (made of calcium bilirubinate consequence of the extravascular hemolysis), and some of these patients will develop cholelithiasis and/or the potential complex sequelae of this condition, i.e. cholecystisis, choledocholithiasis, etc. Diagnostics
Laboratory Testing
Available lab testing that may aid in the diagnosis of HS is as follows:

Coombs Test
Osmotic Fragility Test
Acidified Glycerol Lysis Test
Supportive blood work: mean cell volume (MCV), mean corpuscular hemoglobin concentration (MCHC), red blood cell distribution width (RDW), red blood cell count (RBC), reticulocytes, unconjugated bilirubin, haptoglobin, lactate dehydrogenase (LDH).