Urinalysis and CBC for a 4-Month-Old with Fever, Rhinorrhea, and Cough
Yes, obtain a urinalysis with urine culture, but a CBC is not routinely indicated unless specific clinical features suggest serious bacterial infection or you are considering a chest radiograph based on respiratory findings.
Urinalysis: Strongly Recommended
Physicians should consider urinalysis and urine culture testing to identify urinary tract infection in well-appearing infants aged 2 months to 2 years with fever ≥38°C (100.4°F), especially among those at higher risk 1. Your patient's fever of 39.9°C meets this threshold.
Why UTI Screening is Critical at This Age
Urinary tract infections account for over 90% of serious bacterial infections in infants under 3 months and remain the most common serious bacterial infection in the 2-24 month age group 2, 3.
Risk factors present in many 4-month-olds include: females, fever duration >24 hours, higher fever (≥39°C), and importantly, the presence of a viral infection (suggested by rhinorrhea and cough) does NOT exclude UTI 1, 2.
Up to 30% of children with positive urine cultures have negative urinalysis results, so if clinical suspicion remains high despite negative dipstick, obtain a urine culture anyway 1.
Collection Method Matters
- Use catheterization or suprapubic aspiration for sterile collection 1. Clean-catch has 26% contamination rates versus 12% for catheterization and 1% for suprapubic aspiration 1.
CBC: Not Routinely Indicated in This Clinical Scenario
A CBC is not recommended as a routine test for this presentation. The guidelines do not support routine CBC testing in well-appearing febrile infants aged 2-24 months unless specific criteria are met 1.
When CBC Would Be Indicated
The older 2003 guideline suggested CBC for highly febrile children (>39°C) when considering occult pneumonia, specifically if the WBC count is >20,000/mm³, which then prompts chest radiography 1. However, this approach has been questioned and is not emphasized in the more recent 2016 guidelines 1.
The more contemporary approach focuses on clinical predictors rather than routine laboratory screening 1.
Chest Radiograph Consideration
Given the presence of cough and high fever (39.9°C), consider obtaining a chest radiograph 1.
Clinical Decision Points for Chest X-Ray
The 2016 ACEP guidelines provide Level B recommendations: obtain a chest radiograph in well-appearing infants aged 2 months to 2 years with fever ≥38°C and no obvious source when they have cough, hypoxia, rales, high fever (≥39°C), fever duration >48 hours, or tachycardia/tachypnea out of proportion to fever 1.
Your patient meets two criteria:
Important Caveat
If the clinical picture strongly suggests bronchiolitis with wheezing, do NOT order a chest radiograph 1. The presence of rhinorrhea and cough in a 4-month-old during viral season may represent bronchiolitis, but the absence of documented wheezing and the high fever make pneumonia a consideration.
Critical Pitfalls to Avoid
Do not assume that obvious viral symptoms (rhinorrhea, cough) exclude serious bacterial infection 1, 2. Viral and bacterial infections coexist in this age group.
Do not rely on clinical appearance alone—58% of infants with serious bacterial infections may appear well 2.
Do not skip urine testing in febrile infants, even with an apparent viral source 1. This is the most commonly missed serious bacterial infection.
Practical Algorithm for This Patient
Obtain urinalysis and urine culture via catheterization (Level C recommendation) 1
Assess respiratory status carefully:
Consider chest radiograph given cough + fever ≥39°C (Level B recommendation) 1
CBC is optional and should be reserved for cases where you're evaluating for occult pneumonia or the child appears more ill than expected 1
If wheezing is prominent, skip the chest radiograph (Level C recommendation against) 1