COVID-19: Lab Test

1st order laboratory parameters – obligatory laboratory tests.

  • CBC [lymphopenia/deficiency of lymphocytes (belonging to white blood cells)] (83.2%).
  • Small blood count [leukopenia (deficiency of leukocytes (white blood cells)] (33.7%) [thrombocytopenia/diseased reduction of platelets/platelets] (36.2%)
  • Inflammatory parameters – CRP (C-reactive protein) or PCT (procalcitonin) [CRP: frequently elevated; very high values correlate with poorer prognosis; PCT: usually normal; if values are significantly elevated, bacterial superinfection must be considered]
  • Electrolytes – calcium, chloride, potassium, magnesium, sodium, phosphate.
  • Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT, GGT), alkaline phosphatase, bilirubin [liver dysfunction: about 40%].
  • LDH [↑] (40% of cases) – LDH > 400 IU/ml indicates a more severe course.
  • Renal parameters – urea, creatinine [↑], cystatin C or creatinine clearance, as appropriate.
  • Albumin (serum and urine) + antithrombin 3 – if COVID-19-associated nephritis (kidney inflammation) is suspected, for diagnosis of capillary leak syndrome (synonym: Clarkson syndrome; Engl. “Systemic capillary leak syndrome” (SCLS; condition in which fluid and proteins leak from tiny blood vessels into surrounding tissues; can lead to dangerously low blood pressure (hypotension), hypoalbuminemia, and a decrease in plasma volume (hemoconcentration)); severe deficiency of:
    • Albumin in the blood leads to interstitial pulmonary edema (water lung).
    • Antithrombin III none lead to thrombosis (vascular disease in which a blood clot (thrombus) forms in a vein) and thromboembolism (occlusion of a blood vessel by a detached blood clot)
  • Coagulation parameters – partial thromboplastin time (PTT) [13.2 sec,], Quick, possibly also fibrinogen.
  • Serum ferritin [↑]
  • D-dimer levels [↑; increases only as disease progresses; this is then a sign of impending fatal outcome]
  • Troponin T (biomarker of cardiac injury/damage): high-sensitivity troponin I (hs-TnI) [↑] In a study looking at cardiovascular disease and infection with SARS-CoV-2, it was shown that of 82 patients with elevated hs-TnI, 42 (above the 99th percentile) (51.2%) died in the hospital; the concentration averaged 0.19 µg/l versus 0.006 µg/l in the remaining 334 patients.
  • Creatinine kinase (CK) ↑
  • Blood gas analysis (BGA) – including determination of the main components of blood oxygenation (enrichment of blood with oxygen): oxygen saturation (sO2) and partial pressure of oxygen (pO2).
  • Pathogen detection* by RT-PCR (reverse transcriptase polymerase chain reaction; see “Further notes” below), virus cultivation.
    • Upper respiratory tract: Nasopharyngeal swab (nasopharynx), -rinsing (pharyngeal lavage) or aspirate, oropharyngeal swab [swab in the early phase of infection].
    • Deep airway: bronchoalveolar lavage, sputum (produced or induced as directed), tracheal secretions (two samples should be taken) [swab in the late phase of infection, i.e., a patient who has been symptomatic for 6 to 9 days]
    • Optimal time for detection of infection is day 8 after infection (which is usually day 3 after onset of symptoms): even here, the false-negative rate is still 20% (12 to 30%).
  • Online risk assessment for severe course in COVID-19.

* The laboratory that detects SARS-CoV-2 in a human must report it to the health department. The report must be made immediately and must be received by the health department within 24 hours at the latest. Laboratory parameters 2nd order

  • SARS-CoV-2 antibody detection (IgA/IgM/IgG detection).
    • IgG-specific antibodies can usually be detected at the end of the second week of illness; IgA and IgM a few days earlier.
    • The sensitivity of the test varies depending on the timing of their use after symptom onset in the third week after symptom onset (days 15-39), the sensitivity for IgM is reported to be > 94% and for IgG just under 80%.
    • Cochrane Review: Infections with SARS-CoV-2 are best detected with antibody tests 2 to 3 weeks after the onset of symptoms: by the second week, sensitivity increases to 72.2% (63.5-79.5); by the third week, 91.4% (87.0-94.4) and by the fourth week, 96.0% (90.6-98.3) of all ill patients test positive.
  • IP-10* (interferon-gamma induced protein 10 kD, CXCL10): protein produced by monocytes and macrophages and to a lesser extent by endothelial cells after contact with IFN-γ.
  • MCP-3* (Monocyte Chemotactic Protein 3).
  • IL-6 (Interleukin-6) ↑
  • TNF-α ↑
  • Cortisol ↑ – associated with less favorable course of COVID-19 infection.

* Plasma IP-10 and MCP-3 levels are strongly associated with disease severity and predict progression of COVID-19.

Additional notes

  • The Institute of Virology of the Charité – Universitätsmedizin Berlin offers, designated by the Robert Koch Institute (RKI) as a consiliary laboratory for coronaviruses special tests and expert advice.
  • A negative PCR result does not completely exclude the possibility of infection with SARS-CoV-2. False-negative results cannot be excluded, for example, due to poor sample quality, improper transport, inopportune timing of sample collection, or other reasons (e.g., viral mutation).
  • Testing specimen material from the oropharynx and nasopharynx (nasopharynx) alone is not suitable for ruling out infection. Nonetheless, a Chinese study concludes that reverse transcriptase polymerase chain reaction (RT-PCR) testing detected genes of SARS-CoV-2 in a pharyngeal swab in 162 patients before CT; the test was initially negative in only 5 patients but reached negative in all 5 patients 2 to 8 days later. One possible explanation is that the viruses initially infect the lower respiratory tract and therefore may not necessarily be present in the oral cavity.
  • Note: COVID-19 infection is often detectable by computed tomography (CT) at a time when the polymerase chain reaction is still negative.
  • Triage: important discriminatory parameters for COVID-19 is a temperature above 37.3° Celsius and a lymphocyte count of < 1,100/μl.If both conditions are met, a low-dose CT of the chest should be performed.
  • A first antibody test based on an “enzyme-linked immunosorbent assay” (ELISA) successfully detects antibodies directed against the receptor-binding site on the S protein of SARS-CoV-2.
  • In a pilot study of 89 patients with COVID-19, subsequent lung failure was predicted with higher probability by two laboratory parameters:
    • IL-6 (interleukin-6) level > 80 pg/ml and a CRP level > 9.7 mg/dl.
  • Case series of patients in South Korea who retested positive for SARS-CoV-2 after recovery from COVID-19 disease: The “re-positive” individuals were not shown to have infected others. In 108 “re-positive” cases, attempts were made to isolate the virus from the swabs and propagate it in cultures, but were unsuccessful.