Osmotic Fragility in Red Blood Cells of Pediatric Patients With Cholestatic Liver Disease

Primary Aim:

The primary aim is to determine if ektacytometry of red blood cells is abnormal in a population of pediatric patients over age one with cholestasis.

Secondary Aims:

The secondary aim is to ascertain the extent at which abnormalities in bilirubin levels, bile acid levels, vitamin E levels or cholesterol levels in cholestatic patients are related to changes in red blood cell ektacytometry in this patient population.

BACKGROUND Cholestatic liver disease is an umbrella term for reduced bile flow from either extrahepatic obstruction of bile ducts or faulty hepatocyte bile secretion. Cholestasis is a well-recognized cause of dyslipidemia, and are closely associated with abnormal cholesterol and phospholipid metabolism (3). Cholesterol conversion to bile acids may be impaired, and apo-lipoprotein B binding to cholesterol may be impaired, resulting in the formation of lipoprotein X which contains apo-lipoprotein C (3). The end result of dyslipidemia in cholestatic patients is hypercholesterolemia and an increased membrane cholesterol to phospholipid ratio (3).

The lack of bile entering the digestive tract can lead to increased serum cholesterol, and abnormally high red cell membrane cholesterol: phospholipid ratios, resulting in altered red cell membrane structural integrity (4,5). To test for this phenomenon in patients with extrahepatic biliary atresia, 20 pediatric patients will be tested using ektacytometry to test the deformability and osmotic fragility of red blood cells.

Ektacytometry is a diagnostic tool used to measure the deformability of red blood cells on an osmotic gradient (6). More specifically it measures deformability due to shear stress, while the RBC are suspended in an osmotic medium (6,7). It can differentiate among several blood maladies such as hereditary spherocytosis, hereditary elliptocytosis, Southeast Asian ovalocytosis, and pyropoikilocytosis that are otherwise difficult to diagnose (8). It does this by analyzing rheological behavior under constant shear stress in vitro and using photometric analysis of deformability. This is then quantified and provides a specific ektacytometry curve (Figure 1).

The ektacytometry curve will have several unique features depending on the red blood cell being analyzed. The Omin portion of the curve represents the value of the osmolality in which 50 percent of the red blood cells lyse. The Elmax is the value of the elongation index that reaches its maximum near physiologic osmolality (300 mOsm/Kg). And lastly the Ohyp, which represents the declining portion of the curve and correlates to the initial intracellular viscosity of the cell sample.

To date, ektacytometry has not been employed systematically to characterize potential red cell abnormalities in cholestatic patients. In our analysis the ektacytometry profiles of cholestatic patients will be compared to those of historical non-cholestatic age-matched controls. The degree of fragility will be correlated with serum direct bilirubin levels, serum cholesterol levels, and vitamin E levels.

STUDY DESIGN This pilot study will be a single center, prospective cross-sectional investigation into the ektacytometry of red blood cells taken from 20 cholestatic pediatric patients followed at Cincinnati Children's Hospital. Patients are seen regularly for continued follow up in the hepatology clinic. Parents of all of these patients will be asked to participate in this investigation. The investigators will also contemporaneously analyze ektacytometry of 20 age-matched controls recruited from the general GI clinics with neither cholestatic liver disease nor know red cell membrane defects.

DURATION The study is anticipated to take approximately 6-12 months to complete. This time table includes 3-6 months to recruit patients and perform the assays and another 3-6 months to analyze the data and complete a manuscript.