Differential Diagnosis for Jaundice and 13% Weight Loss in a 6-Day-Old Infant

Single Most Likely Diagnosis

• Breast Milk Jaundice or Breastfeeding-Associated Jaundice: This condition is common in breastfed infants due to substances in the breast milk that can increase bilirubin levels. The significant weight loss could be due to inadequate milk intake or poor latching, which are common issues in the first week of life.

Other Likely Diagnoses

• Infectious Causes (e.g., Urinary Tract Infection, Sepsis): Infections can cause jaundice and significant weight loss in newborns. Early detection is crucial as these conditions can rapidly progress.
• Hypothyroidism: Congenital hypothyroidism can present with jaundice and failure to thrive, including significant weight loss.
• Biliary Atresia: Although less common, biliary atresia is a condition where the bile ducts are blocked, leading to jaundice. It's a surgical emergency and should be considered in infants with persistent jaundice.

Do Not Miss Diagnoses

• Galactosemia: A genetic disorder that affects the body's ability to metabolize galactose, a sugar found in milk. It can cause jaundice, weight loss, and if untreated, can lead to serious complications.
• Congenital Syphilis: Can cause jaundice among other symptoms, and it's crucial to diagnose and treat promptly to prevent long-term sequelae.
• Hereditary Fructose Intolerance: Though rare, this condition can cause severe symptoms after the introduction of fructose-containing foods (like some formulas), leading to jaundice and significant illness.

Rare Diagnoses

• Neonatal Hemochromatosis: A rare condition characterized by iron overload in the newborn period, which can cause liver dysfunction and jaundice.
• Alpha-1 Antitrypsin Deficiency: A genetic disorder that can cause liver disease and jaundice in infancy.
• Tyrosinemia Type I: A rare genetic disorder affecting the breakdown of the amino acid tyrosine, leading to liver and kidney disease, and can present with jaundice and failure to thrive.

Each of these diagnoses requires careful consideration of the clinical presentation, laboratory findings, and sometimes specific diagnostic tests to confirm the diagnosis and initiate appropriate treatment.