What tests should be included in the evaluation of a 4-year-old patient presenting with fever, irritability, runny nose, cough, bilateral conjunctivitis, dry cracked lips, maculopapular rash on the trunk, arms, and legs, and a nontender cervical lymphadenopathy?

Diagnostic Evaluation for Suspected Kawasaki Disease

This 4-year-old with fever, bilateral conjunctivitis, dry cracked lips, maculopapular rash, and cervical lymphadenopathy meets clinical criteria for Kawasaki disease and requires immediate laboratory testing including inflammatory markers (ESR, CRP), complete blood count, comprehensive metabolic panel, urinalysis, and echocardiography to assess for coronary artery involvement. 1

Clinical Diagnosis Confirmation

This patient presents with 5 of 5 principal clinical features of Kawasaki disease:

• Bilateral conjunctivitis (nonexudative) 1, 2
• Oral mucosal changes (dry, cracked lips) 1, 2
• Polymorphous rash (maculopapular on trunk, arms, legs) 1, 2
• Extremity changes (involvement of palms and soles) 1, 2
• Cervical lymphadenopathy (nontender, likely ≥1.5 cm) 1, 2

The presence of fever for one week plus all 5 principal features establishes the diagnosis of classic Kawasaki disease, even though the American Heart Association typically requires only 4 of 5 features. 1

Essential Laboratory Testing

Inflammatory Markers and Baseline Studies

• ESR and CRP - Expected to be elevated; these are the most important initial inflammatory markers 1, 2
• Complete blood count - Look for leukocytosis with left shift, anemia, and later thrombocytosis (typically appears in second week) 1, 2
• Comprehensive metabolic panel - Assess for hypoalbuminemia (<3.0 g/dL), elevated transaminases, and electrolyte abnormalities 1
• Urinalysis - Check for sterile pyuria (>10 WBCs/high-power field), which supports the diagnosis 1

Cardiac Evaluation (Critical Priority)

• Echocardiography - Must be performed immediately at diagnosis to evaluate for coronary artery abnormalities, pericardial effusion, decreased ventricular function, and valvular regurgitation 1
• Electrocardiogram - Assess for arrhythmias, prolonged PR or QT intervals, ST-T wave changes, or low voltage 1
• Cardiac biomarkers (troponin, BNP) - Evaluate for myocardial involvement 1, 3

Additional Supportive Laboratory Tests

The following tests provide supplemental diagnostic support when the diagnosis is uncertain, though this patient has clear classic features:

• Platelet count monitoring - Thrombocytosis (>450,000/mm³) typically develops after day 7 and supports the diagnosis 1
• Albumin level - Hypoalbuminemia (<3.0 g/dL) is a supplemental criterion for incomplete Kawasaki disease 1
• Liver function tests - Mild transaminase elevation may be present 1

Critical Timing Considerations

Treatment with IVIG (2 g/kg) and aspirin must be initiated within 10 days of fever onset to significantly reduce the risk of coronary artery abnormalities from 20-25% to less than 5%. 1, 2 Given this patient has had fever for one week, immediate diagnostic confirmation and treatment initiation are urgent priorities.

The respiratory symptoms (runny nose, cough) are consistent with Kawasaki disease, as cough and rhinorrhea are recognized associated findings, not exclusion criteria. 1 The irritability is also a characteristic neurologic manifestation. 1

Differential Diagnosis Exclusions

While the clinical presentation is classic for Kawasaki disease, testing should exclude:

• Bacterial infections - Blood culture if sepsis is considered, though the nonexudative conjunctivitis argues against bacterial infection 1
• Viral infections - The absence of exudative conjunctivitis, discrete oral lesions, or vesicular rash makes viral etiologies like measles or adenovirus less likely 1, 4
• SARS-CoV-2 testing - Consider PCR and serology to exclude MIS-C, particularly given overlapping features, though this patient's age and presentation are more typical of classic Kawasaki disease 1

High-Risk Features Requiring Intensified Monitoring

This patient's age (4 years old) places them in the typical demographic for Kawasaki disease (80% occur under age 5). 1 However, close monitoring is essential as 15-25% of untreated patients develop coronary artery abnormalities. 1

Repeat echocardiography should be performed at 2 weeks and 6-8 weeks after treatment initiation, with more frequent monitoring if any abnormalities are detected. 1