In the neonatal sepsis workup, which trio of tests is commonly ordered?

• A. CBC with differential, C-reactive protein, and blood culture
• B. Chest radiograph, CRP, and lactate
• C. Serum glucose, calcium, and magnesium
• D. Thyroid function tests, CBC, and urinalysis

Answer: (A)

When evaluating a newborn for possible sepsis, you want a quick mix of tests that show the body’s response to infection and identify the pathogen. The most commonly ordered trio is a CBC with differential, C-reactive protein (CRP), and blood culture. The CBC with differential reveals how the white blood cell count is behaving—leukocytosis or leukopenia and a left shift can signal infection. CRP is an acute-phase protein that rises with inflammation and infection, helping to support the clinical impression. Blood culture is the gold standard for confirming bacteremia and guiding targeted antibiotic therapy. In contrast, the other group includes tests that aren’t routinely used together to screen for sepsis or are more about imaging or metabolic status rather than directly diagnosing infection. Chest radiography may be added if respiratory symptoms are present, but it doesn’t constitute part of the standard initial sepsis workup. Lactate can reflect perfusion, but it’s not part of the typical sepsis triad. Metabolic panels or thyroid/tests with urinalysis don’t specifically address infection in the acute neonatal setting.