Bacterial pneumonia laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Arooj Naz, M.B.B.S

Patients infected with bacterial pneumonia present with a high leukocyte count as well as elevated inflammatory biomarkers, including ESR and C-RP. Red blood cell and platelet count can also be affected presenting as anemia and thrombocytopenia. Arterial blood gasses will often show changes in pH leading to a respiratory acidosis. Other tests routinely done include electrolyte assessment, renal function tests, pulse oximetry, gram staining and sputum samples. Blood cultures and PCR tests are sensitive tests that can provide a definitive diagnosis and aid in the selection of antibiotics.

CBC^[1]

1. RBC: Anemia
2. WBC: Significant leukocytosis (with left shift), leukopenia may present in cases of atypical pneumonia
3. Platelets: Thrombocytopenia

Electrolytes^[1]

• Electrolytes are particularly helpful but hyponatremia may be present in cases of Legionella

Inflammatory biomarkers^[1]

• Erythrocyte sedimentation rate: Elevated
• C-reactive protein: Elevated (> 100 mg/L)

RFTs^[1]

• BUN: elevated

Arterial Blood Gas^[1]

• Hypoxia
• Respiratory acidosis (pH <7.2, bicarbonate <22 mEq/L)

Pulse oximetry^[1]

• < 92% indicates severe hypoxia

Blood Culture^[1]

• Blood culture samples are necessary in diagnosing the bacterial agent responsible. Samples should be taken before administering antibiotics
• A common practice in hospitalized patients

Gram staining^[1]

• Gram staining can identify if an organism is gram positive, gram negative, or does not have a cell wall as in the case of Mycoplasma

Sputum samples^[1]

• Sputum samples should be obtained when patient presents with a productive cough
• A common practice in hospitalized patients

Polymerase Chain Reaction

• PCR results are very rapid and sensitive for detection of bacteria^[2]

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