Differentials
Specific antibody deficiency
SIGNS / SYMPTOMS
Clinical features of lesser severity.
INVESTIGATIONS
Immunoglobulins: normal.
Specific antimicrobial antibodies after immunization: low.
Hyposplenism
SIGNS / SYMPTOMS
May be history of splenectomy, sickle cell disease, celiac disease (also common in IgA deficiency).
INVESTIGATIONS
CBC: thrombocytosis, Howell-Jolly bodies.
Abdominal ultrasound: absence of or small spleen.
Complement deficiency
SIGNS / SYMPTOMS
C3 deficiency predisposes to pyogenic infection; C5b-9 deficiency predisposes to meningococcal and gonococcal infection.
INVESTIGATIONS
Complement function testing: reduced.
Complement component: reduced.
Mannose-binding lectin deficiency
SIGNS / SYMPTOMS
Many patients are asymptomatic. Typically more common in infancy and in the presence of another immunosuppressive factor (e.g., after transplantation).
INVESTIGATIONS
Mannose-binding lectin (MBL) levels: reduced.
Genetic testing: MBL deficiency genotype.
Cystic fibrosis
SIGNS / SYMPTOMS
Positive family history of cystic fibrosis. Infants and children with untreated pancreatic insufficiency may have voracious appetites and never seem satiated. Approximately 10% to 20% of newborns may have delayed passage of meconium or even bowel obstruction with meconium. In males, exam of the scrotum may reveal bilateral absence of the vas deferens.
INVESTIGATIONS
Sweat test: positive (sweat chloride ≥60 mEq/L).
Immunoreactive trypsinogen test: positive.
Genetic testing: presence of 2 disease-causing mutations.
Anatomic anomalies of sinuses/lungs
SIGNS / SYMPTOMS
Other known congenital defects.
INVESTIGATIONS
CT chest and sinuses: abnormalities visible such as obstructive bronchial lesions (e.g., neoplasms in older patients).
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