There are both routine investigations and special case investigations. Routine investigations include sputum analysis, full blood count, and quantitative immunoglobulin levels. Cystic fibrosis and autoimmune testing are done if the patient is suspected of having an underlying condition.

The laboratory findings of bronchiectasis are as follows:^[1]

• Dittrich plugs (foul smelling masses of bacteria), white or yellow concretions
• A gram stain and culture should be performed
  • Evidence of Pseudomonas aeruginosa, Escherichia coli, or Staphylococcus aureus may suggest cystic fibrosis (CF) or allergic bronchopulmonary aspergillosis (ABPA)

• A smear and culture should be performed for Mycobacterium and fungi
• Sputum acid fast bacilli for tuberculosis

• Anemia
• Polycythemia (secondary to hypoxia) in severe cases
• Leukocytosis
• Neutrophilia
• Eosinophilia suggests bronchopulmonary aspergillosis (ABPA)

• Measure IgG, IgA, IgM, and serum electrophoresis to exclude hypogammaglobulinemia.
• Serum IgE, skin prick testing, or IgE radioallergosorbent test (RAST) for ABPA.
  • Diagnostic criteria include a total serum IgE concentration greater than 1000 IU/mL or a greater than 2-fold rise from baseline

• Antibodies to Haemophilius influenzae type B or Streptococcus pneumoniae

• This is used to rule out AAT deficiency

• Screening for PCD-nasal nitric oxide measurements, nasal biopsy and ciliary beat frequency.
• Screening should be performed if there is childhood chronic otitis media, infertility, dextrocardia, or middle lobe bronchiectasis.

• Two measurements of sweat chloride and cystic fibrosis transmembrane regulator (CFTR) genetic mutation analysis should be performed for all children and adults up to 40 years
• The patient should perform cystic fibrosis testing if he is more than 40 years plus
  • Persistent isolation of Staphylococcus aureus in the sputum
  • Features of malabsorption
  • Male primary infertility
  • Upper lobe bronchiectasis
  • History of childhood steatorrhoea.

• If suspected of bronchiectasis secondary to gastrointestinal reflux or aspiration.

• If suspected of an autoimmune disorder such as rheumatoid arthritis.

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