Pediatric Hereditary Elliptocytosis and Related Disorders Workup

Peripheral blood smear

The hallmark of hereditary elliptocytosis is the presence of elliptocytes on the peripheral blood smear (see image below).

Elliptocytes are normochromic and normocytic and may constitute few or all of the patient’s erythrocytes. Spherocytes, ovalocytes, stomatocytes, and fragmented cells may also be observed.

Poikilocytosis (variation in cell shape) and erythrocyte fragmentation are seen in addition to elliptocytosis in patients with severe variants of hereditary elliptocytosis.

Hereditary pyropoikilocytosis erythrocytes are bizarrely shaped (see image below) with fragmentation or budding. The mean cell volume is low, owing to the presence of cell fragments.

Morphology is similar to that seen in patients who have sustained severe thermal burns. Microspherocytosis is commonly found. Distorted, contracted erythrocytes, known as pyknocytes, are prominent in blood smears of neonates with hereditary pyropoikilocytosis.

Parents of infants with signs of hereditary elliptocytosis/hereditary pyropoikilocytosis should undergo examination of their peripheral blood smears to aid in the diagnosis of their child.

CBC count with reticulocyte count

Hemoglobin assay reveals the degree of anemia, if present. A minority of patients with mild hereditary elliptocytosis are anemic.

The reticulocyte count in mild hereditary elliptocytosis is typically less than 5%. In the severe forms of hereditary elliptocytosis and in hereditary pyropoikilocytosis, reticulocyte counts as high as 30% have been reported. High levels of reticulocytosis may compensate for mild anemia.

Markers of hemolysis

Nonspecific markers of increased erythrocyte production and destruction could be evaluated, as in any hemolytic process. These include increased serum indirect bilirubin, increased urinary urobilinogen, increased serum lactate dehydrogenase, and decreased serum haptoglobin.

Osmotic fragility test

Osmotic fragility testing is not typically required. When performed, the results are normal in common hereditary elliptocytosis but reveal abnormal curves in severe hereditary elliptocytosis and in hereditary pyropoikilocytosis. Patients with spherocytic elliptocytosis also have abnormal results.

Controlled thermal stress test

Thermal instability of erythrocytes occurs in hereditary elliptocytosis. Cells fragment at a lower temperature than normal RBCs, and this fragmentation occurs after a shorter period of heating than expected. These tests may be used if membrane protein analysis is unavailable.

DNA testing

Genetic analysis can characterize the molecular defect that results in the clinical and laboratory findings. This is not readily available in all laboratories.

Multiple mutations have been identified. Description of the structure of the erythrocyte spectrin tetramerization domain complex has been accomplished and will further elucidate the structural abnormalities that result in clinically relevant mutations. ^[13]

Genetic analysis can explain clinical severity and inheritance patterns. ^[14] For example, in patients with spectrin mutations, differences in clinical expression are partially related to the spectrin alpha-LELY polymorphism. If this mutation is present on the otherwise unaffected spectrin allele, the disease may be more severe because the concentration of the mutant allele is increased.

Demonstration of a deletion in the SLC4A1 gene is characteristic of Southeast Asian ovalocytosis. ^[15]

Spectrin oligomerization assay

The fraction of spectrin dimers in patients with alpha-spectrin defects correlates well with clinical severity. In individuals with hereditary pyropoikilocytosis and severe hereditary elliptocytosis, spectrin dimers are not converted to tetramers and high percentages of dimers are detected during this assay. ^[2]

Ektacytometry

Ektacytometry measures RBC deformability. ^[16] An ektacytometer is a laser-diffraction viscometer in which deformability is measured as a continuous function of the osmolality of the suspending medium. The Omin point is the osmolality at which the minimum deformability index is reached and is related to the surface area–to-volume ratio of the cell. The Hyper point is the osmolality at which the minimum deformability index reaches half of its maximum value. The Hyper point is related to the internal viscosity of the cell and to its mechanical properties.

In hereditary elliptocytosis, ektacytometry shows decreased maximum deformability characterized by a trapezoidal curve with normal Omin and Hyper points. In hereditary pyropoikilocytosis, the maximum deformability is decreased and the Omin and Hyper points are shifted towards the left. In Southeast Asian ovalocytosis, the key finding is lack of deformability of the erythrocytes. ^[8] Ektacytometry used in combination with gene sequencing, although not readily available, can help to clarify unusual variants. ^[17]

Cation leak testing

Identification of the cation leak in patients who are thought to have hereditary stomatocytosis may be accomplished by comparing the concentration of potassium in the serum of fresh blood with the concentration of potassium in stored refrigerated blood. ^[18]

In patients who are at risk for gallstones, gallbladder ultrasonography should be performed. In patients with severe anemia and congestive heart failure, cardiac echocardiography should be used.