TABLE 2.
Biological investigations in childhood interstitial lung disease
| Investigation | Indicates |
| Haematology | |
| Complete blood count | |
| Reticulocytes | Anaemia and/or diffuse alveolar haemorrhage |
| Haemostasis | Anaemia and/or diffuse alveolar haemorrhage |
| Biochemistry | |
| Serum electrolytes, creatinine | |
| Liver enzymes | Hepatomegaly and/or pulmonary alveolar proteinosis |
| Thyroxine, thyroid-stimulating hormone | Surfactant disorder (NKX2-1) |
| Serum protein electrophoresis, sedimentation rate | Autoinflammatory/inflammatory disorder |
| Angiotensin converting enzyme | Sarcoidosis |
| Iron, ferritin | Anaemia and/or diffuse alveolar haemorrhage and inflammatory syndrome |
| Calcium, ionised calcium, phosphorous | Sarcoidosis |
| Lactate dehydrogenase | Alveolar lung injury |
| Proteinuria | Autoinflammatory/inflammatory disorder |
| Calciuria | Sarcoidosis |
| Ammonaemia | |
| Chromatography of blood and urine amino acids | Metabolic disorder, e.g. lysinuric proteinuria |
| Chromatography of urinary organic acids | |
| Serologies | |
| Epstein–Barr virus serology and viral load | |
| Cytomegalovirus serology and viral load | If subacute, neonatal or immune deficiency |
| HIV-1/HIV-2 serology and viral load | Pneumocystis jirovecii, immune deficiency |
| Mycoplasma pneumoniae serology and nasopharyngeal PCR | Subacute |
| Chlamydia pneumoniae serology and nasopharyngeal PCR | Subacute |
| Chlamydia trachomatis serology and nasopharyngeal PCR | Subacute in newborns |
| Ureaplasma urealyticum serology and nasopharyngeal PCR | |
| IgG precipitins | Hypersensitivity pneumonitis, farmer's lung, bird fancier's lung |
| Immunology | |
| Post-vaccinal serologies | Immune deficiency |
| IgG, IgA, IgM and IgG subclasses | Immune deficiency, autoinflammatory/inflammatory disorder |
| C3, C4, CH50 | |
| Lymphocyte count/differential | |
| Circulating immune complexes | |
| Antinuclear antibodies | |
| ANCAc (PR3), ANCAp (MPO) | |
| Rheumatoid factor | |
| Anti-CCP | |
| Anti-cardiolipin | |
| Scleroderma, polymyositis and myositis antibodies (KU, PM-Scl75, TIF1γ, MDA-5, PM-Scl100, Ml2, KJ; anti-synthetase (PL7, PL12, OJ, centromere, SRP, JO1), smooth muscle, glomerular basement membrane) | Muscular, oesophageal and/or cutaneous involvement |
| GM-CSF auto-antibodies | Pulmonary alveolar proteinosis |
| IFN-α signature, IFN-α dosage | Immune deficiency, autoinflammatory/inflammatory disorder |
ANCA: anti-neutrophil cytoplasmic antibody; PR3: proteinase 3; MPO: myeloperoxidase; CCP: cyclic citrullinated peptide; GM-CSF: granulocyte–macrophage colony-stimulating factor; IFN: interferon.