Blood SampleFever is one of the most common presenting symptom any doctor in pediatric practice will see while working at a medical clinic and has a number of different causes. Sometimes the concerned physician needs to do some basic laboratory workup apart from a detailed history and physical examination to reach the definitive diagnosis and determine the cause of fever.

Laboratory Workup

1. CBC with differential

Often over utilized in well appearing febrile children. High WBC is a risk factor for bacteremia in a highly febrile child. Low WBC count is not a reliable predictor of one specific disease as it may be seen in viral infections, overwhelming infections ( including meningitis) and in immune deficiency states.

The differential helps in identifying acute or chronic infections. In acute bacterial infections there is increased neutrophil count .

2. Lumbar Puncture

Although not done in all children with fever it is a gold standard for diagnosis of meningitis and must be performed whenever history and physical examination are pointing towards the risk of having meningitis.

3. Blood Culture

It has a little value to assess for occult bacteremia (bacteremia unexpected on clinical grounds). Most of these episodes are benign and resolve without treatment. Children who develop serious deep infections often present for medical care before positive test for blood culture.  Multiple (3 or 4) blood cultures are warranted when certain diseases e.g osteomyelitis, endocarditis are suspected, to increase their yield. Blood cultures should be obtained through central lines if present.

4. Urinalysis 

It is a useful test in female children without other evidence of infectious foci; it has significantly lesser yield in male children but should be considered in uncircumcised boys during infancy if fever is not self limited. Urine nitrities, leukocyte esterase , Gram stains and direct cell visualization add to the immediate diagnostic value of urinalysis.

5. Urine Culture

It is the gold standard for diagnosing UTI.

6. Other Cultures

Throat culture and rapid antigen tests can be useful in diagnosing streptococcal pharyngitis. Occasionally culture from the maximum area of induration of a cellulitis yields an infecting organism. Stool culture in selected patients may lead to a diagnosis of enteric infection.

7. Other Miscellaneous tests 

Consider culture of central lines if present. Hepatic transaminases may suggest viral disease and leads to more specific hepatic studies.

C- reactive protein and ESR although nonspecific, can occasionally help direct diagnosis or assess progress of treatment in some infectious diseases.

Radiographic and Other Studies

1.Chest X-Ray

It is useful in patients who have fever without localizing signs, particularly if physical exam findings raise suspicion of pulmonary involvement.

2. Abdominal Imaging

Not done in all cases but it is sometimes done when there is clinical suspicion of abdominal involvement.

3. Ultrasound

Again it is done if clinical signs and symptoms direct an evaluation of a given area. It may reveal abscesses or other fluid collections.

4. Bone scan or MRI

Particularly useful if bone infection is suspected.

5. Thoracocentesis, Arthrocentesis, Bone aspirate

As a general rule, obtaining material for culture from locations of fluid collections has a high yield and is warranted whenever possible. perform whenever possible prior to antimicrobial treatment because it can direct and help in treatment.

6. Echocardiogram

Can be useful to assess for myocardial dysfunction, as seen in viral myocarditis, acute rheumatic fever and Kawasaki disease. May also implicate valvular diseases.

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