Excluding CLL, in which patients would you screen for hypogammaglobulinemia?

Solid tumor patients, other hematologic malignancies, patients with autoimmune diseases on immunosuppressive therapy? Do you consider workup if they are admitted with infectious complications not directly due to their cancer therapy (e.g. not neutropenic, leukopenic). If IgG <400, would you consider IVIG treatment for acute infections, even in the inpatient setting?