Further investigations, suggestive signs and expected abnormal findings according to the underlying aetiology
| Aetiology | Suggestive signs | Additional investigations | Expected abnormalities |
| Cystic fibrosis | Age under 40, malabsorption, poor growth, infertility in males, faecal masses on abdominal x-ray, diabetes | Sweat test | Positive sweat test: chloride concentration >60 mEq/l |
| Genetic testing | 2 CFTR mutations | ||
| NPD | Abnormal NPD | ||
| Congenital disorders | Primary ciliary dyskinesia: sinusitis, otitis media, hearing loss, poor sense of smell, middle lobe predominance | Nasal epithelial brushing or biopsy | Abnormal ciliary beat pattern and frequency of ciliogenesis in culture |
| Nasal NO measurement (>5 years of age) | Nasal NO <150 ppb | ||
| Saccharin test (no clinical value anymore) | Increased time (>60 min) before tasting saccharin | ||
| Marfan's syndrome: myopia, arachnodactylia, tall stature, thoracic deformations, glaucoma, abnormal joint flexibility, heart murmur | Search for major and minor indicators of the disorder | Diagnosis based on family history and a combination of major and minor indicators of the disorder, rare in the general population but occurring in one individual Genetic testing | |
| α1-Antitrypsin deficiency | α1-Antitrypsin deficiency | Levels below 150 mg/dl | |
| Anatomical deformations: visible on clinical examination | Thoracic imaging | Scoliosis or pectus excavatum | |
| IBD | Diarrhoea, abdominal pain, haematochezia, weight loss, arthritis, pyoderma gangrenosum, primary sclerosing cholangitis | Colonoscopy with biopsy of pathological lesions | Biopsy inflammation suggestive of IBD |
| Gastrointestinal advice | |||
| Coeliac disease | Malabsorption, chronic diarrhoea, failure to thrive in children, fatigue, mouth ulcers, anaemia, weight loss, dermatitis herpetiformis | tTG antibodies and IgA | Positive tTG antibodies test without IgA deficiency |
| Endoscopic duodenal or jenunal biopsies | Lymphocytic infiltration, villous atrophy | ||
| Post infectious | History of multiple pulmonary infections, tuberculosis or cough suppression | History or radiological evidence of previous infection | Radiological evidence of previous infection, history of cough suppression |
| Sputum with smear and culture for acid-fast bacilli | Positive for Mycobacterium avium complex or other mycobacteria | ||
| Immunological disorders | Primary: recurrent infections, developmental delay in children, particular organ problems | IgG and subclasses, IgA, IgM | Decreased values, depending on age of patient. Adult: IgG<7.51 g/l; IgA<0.82 g/l; IgM<0.46 g/l |
| Full blood count | Lymphocyte or granulocyte deficit | ||
| Neutrophil antibody and function test, challenge with common humoral bacterial antigens | Result suggestive of antibody presence or impaired function | ||
| Secondary: lung transplant patients, patients under immunosuppressive therapy, HIV | IgG and subclasses, IgA, IgM | Decreased values, depending on age of patient | |
| HIV testing | Positive HIV serology | ||
| ABPA | Asthma, wheezing, coughing up brownish mucoid plugs or blood, upper lobe predominance | Total IgE, sputum sample | Raised total IgE>1000 ng/ml, presence in sputum |
| Specific serum IgE and IgG to Aspergillus fumigatus | Raised Aspergillus IgE and/or IgG | ||
| Aspergillus fumigatus skin prick test | Positive skin prick test | ||
| Rheumatic disorders (RA, SLE, Sjögren, ankylosing spondylitis, relapsing polychondritis) | RA: rheumatoid nodule, arthritis, synovitis, specific skeletal deformities, rheumatoid nodule, other skin symptoms, etc | Autoimmune screening: rheumatoid factor, ANCAs, ANAs and anti-citrullinated peptide antibodies | Diagnosis depending on clinical examination combined with autoimmune screening results (positivity of rheumatoid factor, anti-citrullinated peptide antibodies, ANCAs, ANAs and/or ANA subtypes) |
| SLE: malar rash, ulcers, neuropsychiatric symptoms, etc | Rheumatological advice | ||
| COPD | Dyspnoea, Smoking history, Recurrent infections | Spirometry, bronchodilatation test | Obstructive lung function |
| Traction, obstruction, inhalation | Sarcoïdosis: fatigue, erythema nodosum, lupus pernio, arthralgia, uveitis, Bell's palsy, etc | Chest CT scan | Hilar lymphadenopathy, reticulonodular infiltrates, pulmonary infiltrates, fibrocystic or bullous changes, non-caseating granulomas, upper lobe predominance |
| History of radiation therapy | Biopsy | ||
| History of inhalation/aspiration trauma | Bronchoscopy if imaging showing foreign body | ||
| YNS, Young's syndrome, amyloidosis, endometriosis | YNS: yellow dystrophic nails, lymphoedema, sinusitis, pleural effusion | Exclusion diagnosis based on imaging and clinical findings | |
| Young's syndrome: history of mercury contact, rhinosinusitis, infertility | Urological advice | ||
| Endometriosis: pelvic pain, infertility, cyclic haemoptysis/pain | Gynaecological evaluation | ||
| Idiopathic | Lower lobe predominance, combined chronic rhinitis/sinusitis | All of the above excluded | Exclusion diagnosis |
ABPA, allergic brochopulmonary aspergillosis; ANA, anti-nuclear antibodies; ANCA, anti-neutrophil cytoplasmic antibodies; CFTR, cystic fibrosis transmembrane conductance regulator; COPD, chronic obstructive pulmonary disease; IBD, inflammatory bowel disease; NPD, nasal potential difference; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus; tTG antibodies, tissue transglutaminase antibodies; YNS, yellow nail syndrome.