Laboratory Studies

The degree of neutropenia is important, and a complete blood count with differential is essential. Renal or hepatic dysfunction may reflect acute sepsis or may be preexisting. Acidosis is worrisome for impending sepsis.

Cultures of blood and urine should be obtained, and antibiotics initiated promptly. If an i.v. catheter is present, cultures through each lumen of the catheter should be obtained in addition to a peripheral blood culture. Sputum cultures are low-yield, and bron-choscopy is more useful in the patient with pneumoni-tis. Lumbar punctures are rarely necessary and may be contraindicated in the thrombocytopenic patient. Stool samples for C. difficile and for enteric pathogens and parasites should be obtained in a patient with diar-rheal illness. Any drainage from a catheter site or wound should be sent for Gram stain and cultures.

If bronchoscopy or open lung biopsy is performed, a complete panel of stains and cultures should be sent, including Gram stain and bacterial cultures; fungal; Nocardia; AFB stains and cultures; Pneumocystis stain; Legionella direct fluorescent assay and culture; and cultures for cytomegalovirus (CMV), herpes simplex virus (HSV), and respiratory viruses (influenza, parainfluenza, respiratory syncytial virus (RSV), and adenovirus).

Serologic testing is of limited value in the diagnosis of acute infection in this population. Useful antigen detection tests include cryptococcal antigen in serum or cere-brospinal fluid (CSF), and Histoplasma urinary antigen.

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