Laboratory examination	Lab tests at admission: differential blood count, C-reactive protein (CRP), procalcitonin (PCT), interleukin (IL)-6, kidney and liver values, troponin T, pro-brain natriuretic peptide, immunoglobulin, lymphocyte subpopulation, lactate dehydrogenase (LDH), ferritin, coagulation, D-dimer, lactate, beta-human chorionic gonadotropin in female patients of childbearing age. Daily lab tests: depend on clinical symptoms, important for course of disease: PCT, IL-6, D-dimer, ferritin, differential blood count, liver values, troponin T.
	Typical changes (a)Leucopenia, lymphopenia: frequently, thrombocytopenia (mild) in up to 35% of patients, eosinopenia in up to 52%. (b)CRP increase (in 61–86%) (>10; mostly 10 to 20). (c)LDH increase (in 27–75%). (d)PCT increase (in 24%, especially in patients in intensive care units). (e)Aspartate aminotransaminase/alanine aminotransaminase increase (in 4–22%). (f)Troponin increase.5
	Caveat: Cardiomyopathy with troponin increase is a predictor for increased mortality, especially if troponin increases continuously from day 4. Troponin control is strongly recommended. Troponin increases seem to be connected to a COVID-19-associated cardiomyopathy rather than a myocardial infarction.
Medical imaging	(a)In conventional chest X-ray, changes are visible in 50–60% of patients. However, in computed tomography (CT) scans changes are visible in approximately 85% of cases as ground glass opacity (GGO), bilateral, less frequently unilateral infiltration (14–25%) or increase of interstitial markings (Source: Robert Koch Institute, https://www.rki.de). (b)Chest CT (non-contrast): at admission and for further assessment of course of disease in case of clinical worsening. Long-range indication advisable! (c)CT has higher sensitivity than chest X-ray: chest X-ray abnormal in >60% of patients, CT abnormal in >85%. (d)Typical changes: GGO; bilateral, less frequently unilateral infiltration (14–25%), possible increase of interstitial markings.
Virological examinations	(a)Polymerase chain reaction (PCR): most sensitive non-invasive test. (b)First sample: PCR from deep nasal/throat swab; sensitive in first week (replicative phase in throat area). In case of negative test result but continued clinical suspicion, a second test is advisable. (c)Second sample: lower respiratory passages, for example tracheobronchial secretion (extraction, no bronchoalveolar lavage) or sputum. If pulmonic-infiltrated sputum is detected, then nasal/throat swab (progressive disease). In case of typical clinical picture (and CT) and negative PCR, isolation should be maintained and test repeated. (d)Optional: Influenza A/B and respiratory syncytial virus (quick test). (e)In case of clinical suspicion: sputum bacteriology + mycoplasma + sputum for extensive PCR. (f)Legionella urinary antigen test. (g)Organ- or bone marrow-transplanted/immune-suppressed patients (tumour necrosis factor inhibition): Epstein–Barr virus/cytomegalovirus PCR, adeno-PCR. (h)Aspergillus antigen and beta-glucan in case of clinical suspicion. (i)Blood cultures in case of fever and before empirical antibiosis.