CBC Testing for Common Cold: Not Indicated
A Complete Blood Count (CBC) is not recommended for an otherwise healthy patient with a 6-day history of cough and coryza (common cold) without complications. 1
Why CBC Testing Is Unnecessary
Viral URIs Are Clinical Diagnoses
- The common cold is diagnosed clinically based on symptoms (cough, coryza, sore throat) without requiring laboratory confirmation. 1
- Viral cultures, serologic assays, and laboratory analyses (including CBC) should not be routinely performed because the responsible organism is rarely identified in clinical practice and does not change management. 1
- The diagnosis of acute viral upper respiratory infection does not require blood work when the presentation is typical and uncomplicated. 2
CBC Does Not Distinguish Viral from Bacterial Infection
- A CBC with differential provides information about white blood cell counts and can suggest infection, but it cannot reliably distinguish between viral and bacterial etiologies in respiratory infections. 3
- In the first week of symptoms with cough and coryza, even if sinus inflammation is present on imaging, this represents viral rhinosinusitis and does not indicate bacterial infection requiring antibiotics. 1
- The diagnosis of bacterial sinusitis should not be made during the first week of symptoms, as viral and bacterial presentations are indistinguishable early on. 1
No Impact on Management
- Treatment for the common cold involves symptomatic management with first-generation antihistamine/decongestant preparations, naproxen for discomfort, and supportive care—none of which require CBC results to guide therapy. 1
- Antibiotics have no role in uncomplicated viral upper respiratory infections, regardless of CBC findings. 1, 2
When to Consider Further Evaluation
Red Flags Requiring Assessment (Not Necessarily CBC)
- Pneumonia concerns: If the patient develops abnormal vital signs—heart rate >100 bpm, respiratory rate >24 breaths/min, temperature ≥38°C—or new focal chest examination findings (consolidation, egophony, fremitus), chest radiography is indicated to rule out pneumonia, not CBC. 1
- Pertussis suspicion: If cough persists ≥2 weeks with paroxysms, post-tussive vomiting, or inspiratory whooping, obtain nasopharyngeal culture for Bordetella pertussis, not CBC. 1
- Prolonged symptoms: If cough persists beyond 8 weeks, systematic evaluation for chronic cough causes (upper airway cough syndrome, asthma, GERD) is warranted, but CBC remains unnecessary unless specific complications arise. 1, 4
Common Pitfall to Avoid
- Do not order CBC or other laboratory tests simply because a patient presents with respiratory symptoms lasting less than one week. This represents low-value care that increases costs without improving outcomes. 1, 2
- The natural history of viral URI includes cough lasting up to 3 weeks in many patients (58% cough for at least 2 weeks, 35% for 3 weeks), which does not indicate bacterial infection or warrant laboratory investigation. 5
Bottom Line
For a healthy patient with 6 days of cough and coryza, no laboratory testing including CBC is indicated. 1 Focus on symptomatic treatment and patient education about the expected 2-3 week duration of symptoms. 4, 2