For an older adult or patient with a history of respiratory issues presenting with new onset of cough and crackles at the lung bases, should I order a Complete Blood Count (CBC) and Basic Metabolic Panel (BMP) as part of the initial diagnostic workup?

Diagnostic Workup for New Onset Cough with Basilar Crackles

No, do not routinely order CBC and BMP for a patient with new onset cough and basilar crackles—instead, immediately order a chest X-ray, measure vital signs (temperature, respiratory rate, heart rate, oxygen saturation), and obtain C-reactive protein (CRP) if available, as this clinical presentation is highly suggestive of pneumonia. 1, 2

Essential Initial Tests

The priority diagnostic approach focuses on confirming or excluding pneumonia through imaging and inflammatory markers, not routine blood counts or metabolic panels:

• Chest radiography (PA and lateral views) is the essential first test when crackles are present with new cough, as the combination of breathlessness, crackles, and diminished breath sounds significantly increases pneumonia likelihood 1, 2
• Vital signs assessment including temperature (fever ≥38°C), respiratory rate (tachypnea >25/min), heart rate, and oxygen saturation is crucial in the initial diagnostic approach 1, 2
• C-reactive protein (CRP) should be measured because CRP >30 mg/L combined with crackles and fever substantially strengthens the diagnosis of pneumonia, while CRP <10 mg/L makes pneumonia less likely 1, 2

Why CBC and BMP Are Not Recommended

The American College of Chest Physicians guidelines for acute cough and suspected pneumonia make no mention of CBC or BMP as part of the routine diagnostic workup 1. These tests do not change management decisions in outpatient pneumonia and are not included in evidence-based diagnostic algorithms 1, 2.

The guideline explicitly states there is no need for routine microbiological testing unless results would change therapy 1, and this principle extends to routine blood work that doesn't inform the pneumonia diagnosis or treatment decision.

When Additional Testing May Be Warranted

CBC and BMP become relevant only in specific clinical scenarios:

• Abnormal vital signs suggesting need for hospitalization (respiratory rate >30/min, oxygen saturation <90%, systolic blood pressure <90 mmHg) where severity assessment requires laboratory evaluation 2
• Elderly patients (≥70 years) with altered mental status or concern for sepsis 1, 2
• Suspected complications such as dehydration, electrolyte abnormalities, or severe infection requiring admission 2

Clinical Decision Algorithm

Follow this structured approach:

1. Assess vital signs immediately - fever, respiratory rate, heart rate, oxygen saturation 1, 2
2. Order chest X-ray - this is the definitive test for pneumonia diagnosis 1, 2
3. Obtain CRP if available - adds diagnostic value when combined with clinical findings 1
4. Do NOT routinely order procalcitonin (adds no value), CBC, or BMP unless severity indicators present 1

Management Based on Findings

If pneumonia is confirmed or highly suspected:

• Initiate empiric antibiotics according to local community-acquired pneumonia guidelines immediately 1, 2
• No routine microbiological testing needed in outpatient settings unless results would change therapy 1

If vital signs are normal and chest X-ray is negative:

• Do not prescribe antibiotics routinely 1
• Consider alternative diagnoses: early pneumonia, influenza, postinfectious cough, bronchiectasis, or interstitial lung disease 1, 2, 3

Critical Red Flags Requiring Expanded Workup

Order CBC, BMP, and consider hospitalization if any of these are present:

• Hemoptysis, weight loss, or night sweats 2
• Persistent fever despite initial treatment 2
• Progressive dyspnea or oxygen saturation <90% 2
• Immunocompromised state 2
• Altered mental status in elderly patients 1, 2

Common Pitfalls to Avoid

Do not delay chest X-ray to wait for laboratory results - imaging is the priority test and directly informs treatment decisions 1, 2. The presence of crackles with cough has high clinical significance for pneumonia and requires radiographic confirmation, not blood work 1, 4.

Do not attribute crackles to benign causes without imaging, especially in patients with fever, dyspnea, or risk factors for serious disease 1, 2. Elderly patients may have atypical presentations with minimal symptoms despite significant radiographic findings 1, 4.