High MCHC or stomatocytes on the blood smear

Stomatocytes have a mouth-shaped instead of a round area of central pallor. In many cases, stomatocytes comprise more than half of RBCs. Stomatocytosis can be heritable or acquired. If a specific genetic cause is known in the family, testing for the familial variant can be performed. Hematologist input is appropriate for any suspected heritable syndrome, any acutely ill individual, or any management considerations that depend on the underlying cause of stomatocytosis, including indications and contraindications of splenectomy, and management of iron overload. Refer to UpToDate for additional details.

Stomatocyte-like RBCs may be found on the blood smear in Southeast Asian ovalocytosis (SAO), a separate disorder caused by a specific nine amino acid deletion in Band 3 (SLC4A1 gene). Refer to UpToDate discussion on SAO for typical findings and diagnostic evaluation.