Note: specimen must not be older
than 4 hours from time of phlebotomy. This EDTA-anticoagulated plasma-only test
for brain (beta-type) natriuretic peptide
(BNP) can be run on such as the desk-top Triage system
or a fluorescent system. [the
vendor]
BNP is elevated when increased wedge pressure or "stretch"...stress...is
placed on one or both cardiac ventricles...whether yet causing
symptoms or not. The test module was created for easy & early
detection of new cases or relapses of congestive heart failure
(CHF) in patients with shortness of breath (SOB), onset of cough,
or abnormal chest X-ray. It is estimated that more than 5,000,000
US citizens suffer CHF. Elevations will also occur in systemic
hypertension (if it is causing chronic "stretch" leading
to ventricular enlargement). Uncomplicated COPD and bronchiolitis/pneumonia
do not elevate BNP. However, pulmonary emboli sufficiently obstructive
to produce increased ventricular stretch will elevate BNP.
BNP identifies patients with cardiac "pump dysfunction", stretch, or stress.
BNP is elevated in both diastolic (diabetic effect, toxic effect,
or drugs that affect myocardium...such as chemotherapy drugs) and
systolic dysfunction (echocardiogram abnormal only in systolic
dysfunction) AND even when ejection fraction is preserved5!
ER use: When accurately deployed, the
test helps in every ER case of shortness of breath of seriously-uncertain
etiology. It helps settle the classical patient-case disputes between
pulmonologists and cardiologists as to whether CHF is any of the
cause of the symptoms/abnormal chest X-ray, or not. The half-life
of BNP is short; so, to prove proper CHF treatment response, BNP
levels can be followed for expected declines in about 2 days. We've
sent this test out to reference labs as of12/2002; we were in the
implementation phase for on-site testing at the LMC main lab as of 19 May 2003
(in use as of mid-June 2003).
Although ER doctors must take many factors into account
in the diagnosis of CHF, a BNP of less than 100 pg/mL makes CHF
dyspnea highly unlikely (although some cases with mild dyastolic dysfunction but preserved ejection fraction even have a BNP no higher than about 405), 100-400 is indeterminate, and greater
than 400 gives a 95% likelihood of CHF2 (a cardiac
pump dysfunction). When greater than 500, CHF (a cardiac pump dysfunction)
is highly likely. From another perspective, a rule of thumb is that a level >100
is abnormal.
For CHF inpatients: It may prove to
be a critical safety factor to repeat BNP prior to discharge and
be sure that it has improved concordantly with sign & symptom
improvement. |
