Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (754 page)

   Infectious diseases and fever of unknown etiology (cultures, organism identification)

   Limitations

   Bone marrow aspirate may be diluted with peripheral blood and contain too few cellular elements.

   Bone marrow biopsy may have insufficient tissue for accurate diagnosis; the underlying condition may result in patchy infiltrations of the marrow (e.g., myelomas), and the pathology may be missed.

BRAIN NATRIURETIC PEPTIDE (BNP)

   Definition

   Other names include B-type natriuretic peptide,
N
-terminal pro b-type natriuretic peptide, and NT-proBNP. BNP is a hormone secreted by myocytes in the ventricles (left ventricle) in response to pressure overload/myocyte stretch, with potent diuretic, natriuretic, and vascular smooth muscle relaxing effects. The heart normally produces low levels of a precursor protein, pro-BNP, which is cleaved to release the active hormone, BNP, and an inactive fragment, NT-proBNP.

   
Normal range:

   BNP: <100 pg/mL

   NT-proBNP: 0–74 years of age: ≤124 pg/mL; 75 years of age and older: ≤449 pg/mL

   Use

   Screening and diagnosis of CHF: BNP and NT-proBNP levels in the blood may be useful to establish prognosis in heart failure because both markers are typically higher in patients with worse outcome.

   Reading >480 pg/mL = 51% chance of cardiac/noncardiac events in next 6 months.

   Reading <230 pg/mL = 2.5% chance of cardiac/noncardiac events in next 6 months.