Glossary of Clinical Laboratory: Cardiac Enzymes
Other Decks By This User
- What are enzymes?
- -substances produced by various organs that facilitate chemical reactions
- Enzyme measurements are based on ..
- activity not quantity
- Why do we measure enzymes?
- to gain info concerning specific organ function
- Comparison in intracellular and plasma enzyme levels?
- Intracellular enzyme levels are much higher then plasma levels
- Reasons for elevated plasma enzymes levels?
- background for Cardiac enzymes
- -when cardiac cells die, they release enzymes thus measuring enzymes can assess cell death
-serial measurements are made to assess cardiac damage
-serum measurement is the specimen of choice
- When are cardiac enzyme measurement taken?
- Types of cardiac enzymes?
- -aspartate aminotransferase (AST) - formerly SGOT
-Lactate dehydrogenase (LDH)
-Creatine Kinase (CK)
- -aspartate aminotransferase
-enzyme used by heart cells
-released after cells are damaged
- AST and MI
- -AST in elevated 90-95% of acute MI pts
-elevation seen in 8-12 hrs
-peak 24-48 hours
-return to normal 3-8 days
- Causes of AST elevation:
-damage to liver, kidney, skeletal muscle, pancreas (good sensitivity, poor specificity)
-certain drugs (demorol, coumadin)
- -lactate dehydrogenasee
-released with damage to liver, kidney, skeletal muscle, RBCs, WBCs, lung, and tumor tissue
-good sensitivity, poor specificity
-samples are very sensitive to hemolysis
-NOT A GOOD CARDIAC INDICATOR
-NOT A RELIABLE PREDICTABLE OF MI IF OTHER DAMAGE OR SURGERY HAS OCCURED
- LDH supports dx of unjury or dz involving:
- LDH isoenzymes:
- LDH1 17-27% mainly heart
LDH2 27-37% RE system (RBC)
LDH3 18-25% Lungs
- LDH and MI
- -elevated in 92-95% of all acute MI pts
-LDH1 and LDH2 ratios are reversed
-elevated 24-48 hours
-peaks 48-72 hours
-normalized 5-10 days
- Ratio appears in 12-24 hours and is 80% specific
-slighly more sensitive than AST
**Rarely used anymore because too late of detection (too late elevation)
- Creatine Kinase
- -involved in conversion of creatine phosphate to creatine in muscle contraction
- Where is creatine Kinase is located?
- -found mainly in the heart, skeletal muscle, and brain tissue
-damage to any these tissue will elevate the total CK
- Creatine Kinase indications?
- -used to support diagnosis of myocardial injury
-may indicate neurological or skeletal muscle damage
- CK Isoenzymes:
- MB: heart fraction 0%
MM: Skeletal muscle 100%
BB: brain and lung 0%
- CKMB and MI
- -elevated in 90-93% of all acute MI pts
-CKMB rises in 3-6 hrs after MI
-CKMB peaks in 12-24 hrs
-CKMB normalizes within 12-48 hrs
- CKMB usually rises in..
- -unstable angina
- CKMB does not usually rise in..
- What is used to avoid misdiagnosis of MI?
- -ratio of MB: total CK
-a CKMB of 3.0 ng ml with a relative index of >2.5 is highly suggestive of an MI
- CKMB is useful in...
- -quantifying degree of MI and timing the onset and appropriateness of thrombolytic therapy
- What causes a rise in AST and LD but not in CK?
- acute liver disease
- Total CK rises in...
- -moderate strenuous exercise
- Total CK and hypothyroidism and hyopkalemia
- -elevated in 80% of pts with hypothyroidism or hypokalemia due to muslce damage
- Benefits of CK?
- -CKMB can help sort out MI versus strained muscle etc
-normalizes in 12-48 hours
-CKMB does not rise with angina, PE, or CHF
-CK does not rise with acute liver damage (unlike AST and LD)
- Normal CK value is based on...
- patient size and muslce mass
- Is single value of CK useful?
- single value is of little value; need to look at trend over time
- CKMM is elevated in...
- -skeletal muslce injury
- When should CK measurements be taken?
- What are Troponins?
- -proteins that exist in skeletal and cardiac muscle
-2 types: T and I
- What do Troponins do?
- -help regulate muscle contraction
- How are cardiac specific troponins separated?
- -using monoclonal antibodies or ELISA techniques
- Troponin values:
- TN T <0.2 ng/ml
TN I < 0.3 ng/ml
- Troponin elevation, peak, normalization times:
- Elevates: 2-6 hours
Peaks: 12-16 hours
TN I normalizes: 7-10 days
TN T normalizes: 10-14 days
- TN vs CKMB
- -CKMB can be elevated in severe muscle, brain, or lung injury, or renal failure whereas troponins are always normal in non-cardiac injury
-troponins elevate sooner then CKMB (2-6 hours compared to 3-6 hours)
-troponins stay elevated longer (normalize later) than CKMB (7-10 or 10-14 days compared to 24-48 hours)
- So if TN I is so good, why bother with CKMB at all?
- because TN I remains elevated for 7-10 days whereas CKMB normalizes within 12-48 hours so you can tell if the pt re-infarcts
- Disadvantages to Troponin?
- Not helpful for reinfarct
cannot tell if elevation is old or new
- Indication for Troponin?
- -Eval chest pain since they are extraordinary specific for myocardial cell injury
-determine cardiac iscehmia
-differentiate cardiac from non-cardiac chest pain
-eval of pts with unstable angina (divides those with lasting dysfcn from those without)
-may decide if thrombolytic therapy is appropriate
- What is Myoglobin?
- -oxygen binding protein found in cardiac and skeletal muslce
-NOT AN ENZYME!!
- When is myoglobin test indicated?
- -early eval of pt with suspected MI (provides early index of damage to myocardium)
-dx disease or injury to skeletal muscle
- when does Myoglobin elevate?
- rises: 0-3 hours
peaks: 6-8 hours
normalizes: 20-36 hours
- Myoglobin vs CK
- -myoglobin is more sensitive than CK isoenzymes but less specific (any trauma or injury may elevate myoglobin)
- Cardiac enzymes elevation comparison
- Myoglobin (0-3 hr)
Troponin (2-6 hr)
CKMB/ CKtotal (3-6 hr)
AST (8-12 hr)
LDH (24-48 hr)
- Cardiac enzymes normalization comparison
- CKMB (12-48 hr)
myoglobin (20-36 hrs)
AST (3-8 days)
LDH (5-10 days)
Troponin I (7-10 days)
- Cardiac enzymes specificity comparison
- troponin (cardiac injury ONLY)
- Cardiac enzymes sensitivity comparison
- myoglobin (most sensitive, BUT not enzyme)
- Cardiac enzymes peak comparions
You must Login or Register to add cards