Laboratory findings associated with parotitis will vary depending on the cause. Presence of the mumps virus, Staphylococcus aureus, HIV, and extrapulmonary tuberculosis, determined by laboratory testing, are indicative of parotitis causation. Additionally, findings for all causes of parotitis include markers for inflammation as well as elevated white blood cell counts.

A parotitis patient should undergo the following laboratory tests to determine the cause:

• The primary mumps tests include the following:^[1]
  • Real-time polymerase chain reaction: used to detect the mumps RNA in oral samples.^[2]
  • Mumps cell culture: obtaining and isolating mumps viral culture via an oral or buccal specimen swab.^{_Lab_Testing_Questions_and_Answers_|_CDC-3|[3]}
  • Serological tests to determine presence of IgM antibodies indicative of mumps.

• The following tests are performed to determine the presence of Staphylococcus aureus as the cause of parotitis:
  • Oral or buccal swab to obtain the potential specimen.
  • Gram staining: Determining if the bacteria obtained is gram-positive^[4]
  • Culturing in mannitol salt agar to determine if yellow-colored colonies emerge, indicative of Staphyloccocus aureus
  • Real-time polymerase chain-reaction.^[2]

• The following tests are performed to determine HIV-caused parotitis:
  • ELISA: Used to detect presence of antibodies and antigens for HIV.^{_HIV_Basics_|_HIV/AIDS_|_CDC-5|[5]}
  • Nucleic acid test: Used to detect the presence of HIV in the blood.

• Parotitis from extrapulmonary tuberculosis can be determined by the following:
  • Interferon-Gamma Release Assays (IGRAs): IGRAS measure immune system reactivity to M. tuberculosis.
    • White blood cells from most people that have been infected with mycobacterium tuberculosis will release interferon-gamma (IFN-g) when mixed with antigens derived from M. tuberculosis.
    • High (IFN-g) values in a parotitis patient is indicative of extrapulmonary tuberculosis.^{_TB_|_Fact_Sheets_|_Interferon-Gamma_Release_Assays_(IGRAs)-6|[6]}

• White Blood Cell Count
  • A complete blood count test performed on parotitis patients may reveal abnormal lymphocyte and other white blood cell counts, lesser or greater than normal.
• Markers for Inflammation
  • Parotitis patients may display markers for inflammation, determined by the following tests:
    • Erythrocyte sedimentation rate
    • C-reactive protein