From the Guidelines
To check for infection, laboratory tests should include a complete blood cell (CBC) count with differential leukocyte count and platelet count, as well as measurement of serum levels of creatinine, blood urea nitrogen, electrolytes, hepatic transaminase enzymes, and total bilirubin 1. When evaluating a patient for infection, it is crucial to consider a range of laboratory tests to guide diagnosis and management.
- Key tests include:
- CBC with differential to assess for leukocytosis or leukopenia
- Serum creatinine and blood urea nitrogen to evaluate renal function
- Electrolytes, hepatic transaminase enzymes, and total bilirubin to assess for any organ dysfunction
- In addition to these tests, at least 2 sets of blood cultures are recommended, with one set collected from each lumen of an existing central venous catheter (if present) and from a peripheral vein site 1.
- Culture specimens from other sites of suspected infection should also be obtained as clinically indicated, such as urine, wound, or respiratory cultures 1.
- A chest radiograph is indicated for patients with respiratory signs or symptoms to evaluate for pneumonia or other pulmonary infections 1. The choice of laboratory tests should be guided by the patient's clinical presentation, suspected site of infection, and underlying medical conditions. Results should be interpreted in the context of the patient's overall clinical picture, as some infections may not immediately show laboratory abnormalities, particularly in early stages or in immunocompromised patients.
From the Research
Labs to Check for Infection
To diagnose infections, several laboratory tests can be used, including:
- Complete Blood Count (CBC) and differential leukocyte count (DC) [ 2 ]
- C-reactive protein (CRP) test [ 2, 3, 4 ]
- Procalcitonin (PCT) test [ 2 ]
- Erythrocyte sedimentation rate (ESR) test [ 3, 4 ]
Interpretation of Lab Results
When interpreting lab results, it is essential to consider the following:
- CRP is more useful in diagnosing acute infections, while ESR is helpful in monitoring chronic inflammatory conditions [ 3 ]
- Many factors can result in falsely high or low ESR and CRP levels, and it is crucial to take note of these [ 3, 4 ]
- ESR and CRP lack sensitivity or specificity, so these tests should be used only in combination with clinical history and physical exam for diagnosis and monitoring of pathological conditions [ 4 ]
Machine Learning Models
Machine learning models, such as random forest models, can be used to predict bacteremia using CBC/DC data, and have shown promising performances [ 2 ]
- These models can achieve an area under the ROC curve (AUC) of 0.802, which is superior to the prediction conventionally made with CRP/PCT levels [ 2 ]
- The addition of CRP or PCT to CBC/DC data does not substantially increase the AUC, suggesting the predicting power and applicability of using only CBC/DC data [ 2 ]