What additional labs should be ordered for a patient with a temperature of 38 degrees?

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Last updated: June 16, 2025View editorial policy

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From the Guidelines

For a patient with a temperature of 38 degrees Celsius, I strongly recommend ordering a complete blood count (CBC) with differential, blood cultures (two sets from different sites), urinalysis with culture, and a comprehensive metabolic panel (CMP) to promptly identify the underlying cause of fever and guide appropriate management. The patient's symptoms and clinical presentation should guide the selection of additional targeted tests, which may include:

  • Chest X-ray for respiratory symptoms
  • Throat culture for pharyngeal symptoms
  • Lumbar puncture if meningitis is suspected Inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can help assess the severity of inflammation, as suggested by 1. Procalcitonin may be useful to distinguish between bacterial and viral infections, as indicated by 1. These tests are essential because fever indicates an inflammatory response that could be due to infection, malignancy, autoimmune disorders, or medication reactions. The CBC can reveal leukocytosis suggesting bacterial infection or lymphocytosis suggesting viral infection, while blood cultures can identify bloodstream infections, as noted in 1. The urinalysis and CMP provide information about potential sources of infection and organ function that might be affected by the underlying cause of fever. It is crucial to consider the patient's overall clinical presentation and medical history when interpreting the results of these tests and guiding further management. In cases where pericardial disease is suspected, additional tests such as transthoracic echocardiography, chest X-ray, and routine blood tests, including markers of inflammation, may be necessary, as recommended by 1. However, the initial focus should be on identifying the underlying cause of the fever and managing any potential infections or inflammatory responses promptly.

From the Research

Additional Labs for a Patient with a Temperature of 38 Degrees

To determine the additional labs that should be ordered for a patient with a temperature of 38 degrees, we need to consider the potential underlying causes of the fever and the diagnostic tools that can help identify these causes.

  • A complete blood cell count (CBC) can be a powerful diagnostic tool, as stated in the study 2, and should be considered as part of the initial workup.
  • A chemistry panel and urinalysis, as mentioned in the study 2, can also provide valuable information and should be included in the minimum database.
  • Liver function tests, such as those discussed in the study 3, may be useful in detecting sepsis in its early stages, especially if bacteremia is suspected.
  • Electrolyte panels, including potassium and chloride, as well as blood urea nitrogen and creatinine, can help assess renal function and acid-base homeostasis, as discussed in the study 4.
  • Troponin I levels, as mentioned in the study 5, may be elevated in patients with sepsis and can indicate subclinical myocardial injury.

Considerations for Lab Orders

When ordering labs, it is essential to consider the clinical context and the potential underlying causes of the patient's symptoms.

  • The choice of labs should be guided by the patient's history, physical examination, and initial diagnostic findings.
  • The study 6 highlights the importance of establishing reference intervals for laboratory tests, which can help guide the interpretation of results and inform clinical decision-making.
  • By considering the potential causes of the patient's fever and ordering a targeted set of labs, healthcare providers can gather more information and develop an effective plan of care.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

The complete blood cell count: a powerful diagnostic tool.

The Veterinary clinics of North America. Small animal practice, 2003

Research

Liver function tests in patients with bacteremia.

Journal of clinical laboratory analysis, 2008

Research

Abnormal Basic Metabolic Panel Findings: Implications for Nursing.

The American journal of nursing, 2020

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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