Etiology of cholelithiasis is either increased cholesterol, increased bilirubin, or decreased bile salts. For increased cholesterol look for recent history of rapid weight loss or a familial hyperlipidemia. For decreased bile salts look for Celiac disease, Crohn’s, or Cystic Fibrosis. The most common cause in pediatrics is an increased production of bilirubin secondary to an RBC abnormality. For this, look for Sickle Cell Disease or Hereditary Spherocytosis. Specifically, for Hereditary Spherocytosis you should see an increased MCHC on CBC, note that this is not specific to Hereditary Spherocytosis and is merely suggestive, further testing would be needed.