Table 1.

Features of primary disorders of erythrocyte volume homeostasis

	Overhydration syndromes			Intermediate syndromes		Dehydration syndromes
Condition	Overhydrated hereditary stomatocytosis (hydrocytosis)	Mild hereditary stomatocytosis	Cryohydrocytosis	Stomatocytic xerocytosis	Xerocytosis with high phosphatidyl-choline	Xerocytosis	FP
Hemolysis	Severe	Mild to moderate	Mild to moderate	Mild	Mild to moderate	Moderate	None
Anemia	Severe	Mild to moderate	Mild to moderate to compensated	None	Moderate	Mild to moderate	None
Blood smear	Stomatocytes ± spherocytes	Stomatocytes and/or spherocytes	Stomatocytes ± spherocytes ± targets	Stomatocytes	Targets, echinocytes	Targets, rare stomatocytes, or dessicytes	Rare target or stomatocyte
MCV (80-100 fL)*	110-150	95-130	90-105	91-98	100-110	90-110	82-104
MCHC (32-36g/dL)	24-30	26-30	34-40	33-39	34-38	34-38	33-39
Unincubated osmotic fragility	Very increased	Increased	Variable	Decreased	Very decreased	Decreased to very decreased	Slightly decreased
RBC Na+ (5-12 mEq/LRBC)	60-150	30-60	15-100	10-20	10-20	5-30	10-25
RBC K+ (90-103 mEq/LRBC)	20-55	40-85	30-100	75-85	60-80	60-100	75-110
RBC Na+ + K+ (95-110 mEq/LRBC)	110-170	115-145	70-130	87-103	75-90	70-110	85-110
Phosphatidyl-choline content	Normal	± Increased	Normal	Normal	Increased	Normal or increased	Normal
Cold autohemolysis	No	Unknown	Yes	No	Unknown	No	No
Pseudohyperkalemia	Sometimes	Unknown	Yes	Sometimes	Sometimes	Sometimes	Yes
Effect of splenectomy†	Good	Good	Little or no effect	Unknown	Unknown	Poor	Not applicable
Thromboembolism risk postsplenectomy	Yes	Unknown	? Yes	Unknown	Unknown	Yes	Unknown
Inheritance	Autosomal dominant	Autosomal dominant	Autosomal dominant	Autosomal dominant	Autosomal dominant	Autosomal dominant, de novo	Autosomal dominant
Gene defects	RHAG	SLC4A1	SLC4A1, GLUT1	PIEZO1, unknown	PIEZO1, unknown	PIEZO1, KCNN4	ABCB6, PIEZO1

Modified in part from Lux¹²² with permission.

K⁺, potassium; LRBC, liter of red blood cells; MCV, mean corpuscular volume; Na⁺, sodium; PC, phosphatidylcholine; RBC, red blood cell.

^*Values in parentheses are the normal range.

^†Splenectomy is contraindicated in these disorders.