Page 125 - Critical Care Nursing Demystified

110 CRITICAL CARE NURSING DeMYSTIFIED

are generally higher than LDH1 levels. In the case of an MI, the opposite situ-
ation occurs.
LDH3 – Is found in the lungs, spleen, pancreas, thyroid, adrenal glands, and
lymph nodes
LDH4 and LDH5 – Are the hepatic fractions found mostly in the liver and
skeletal muscle.
Normal range of LDH percentages – LDH1, 17% to 33%; LDH2, 27% to
37%; LDH3, 18% to 25%; LDH4, 3% to 8%; and LDH5, 0% to 5%.

Troponin
Gold standard cardiac markers that have evolved to evaluate myocardial dam-
age are the troponins. Troponins are proteins that are highly specific to cardiac
muscle and will increase early and rapidly in the bloodstream as does the
CK–MB after an MI. Troponins are NOT detected in healthy individuals and
any muscle injury other than the heart. Troponins occur in various forms:
Troponin I – Rises in 4 to 6 hours, peaks in 14 to 18 hours, and remains
elevated for 5 to 7 days. The normal range is 0 to 2 ng/mL.
Troponin T – Available for rapid cardiac damage assessment, as well as Downloaded by [ Faculty of Nursing, Chiangmai University 5.62.158.117] at [07/18/16]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.
predicting the prognosis for patients with acute coronary destruction. These
troponins will increase in 3 to 4 hours and remain elevated for 10 to 14 days.
The normal range is 0 to 0.2 ng/mL.

NURSING ALERT
Cardiac troponin remains detectable in the peripheral circulation for 8 to 12 hours
after the onset of an MI and is the gold standard for early diagnosis of an MI. Many
sources indicate differences in troponin testing and the interpretation of results. The
above examples are only approximations and may vary according to health care
facility standards and laboratory protocols.

Myoglobin
Myoglobin is another important cardiac enzyme (marker) that can be used in
the earliest detection of an MI. It is released within 30 to 60 minutes after an
MI with a normal value that is gender specific. Normal values for males are less
than 72 ng/mL and are less than 50 ng/mL in women. A myoglobin in combina-
tion with other markers helps in the detection of an MI but is not used solely
to make a diagnosis.