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50 Cards in this Set
- Front
- Back
What are enzymes?
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-substances produced by various organs that facilitate chemical reactions
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Enzyme measurements are based on ..
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activity not quantity
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Why do we measure enzymes?
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to gain info concerning specific organ function
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Comparison in intracellular and plasma enzyme levels?
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Intracellular enzyme levels are much higher then plasma levels
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Reasons for elevated plasma enzymes levels?
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-stress
-injury -necrosis |
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background for Cardiac enzymes
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-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 |
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When are cardiac enzyme measurement taken?
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admission
2-4 hours 6-8 hours 12 hours |
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Types of cardiac enzymes?
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-aspartate aminotransferase (AST) - formerly SGOT
-Lactate dehydrogenase (LDH) -Creatine Kinase (CK) -Troponin |
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AST
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-aspartate aminotransferase
-fomerly SGOT -enzyme used by heart cells -released after cells are damaged |
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AST and MI
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-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 |
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Causes of AST elevation:
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-MI
-damage to liver, kidney, skeletal muscle, pancreas (good sensitivity, poor specificity) -certain drugs (demorol, coumadin) -chornic hypokalemia |
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LDH
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-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 |
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LDH supports dx of unjury or dz involving:
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-heart
-liver -RBCs -Kidney -Skeletal muscle -brain -lungs |
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LDH isoenzymes:
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LDH1 17-27% mainly heart
LDH2 27-37% RE system (RBC) LDH3 18-25% Lungs LDH4 Kidneys/placenta LDH5 Liver/muscle |
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LDH and MI
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-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) |
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Creatine Kinase
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-involved in conversion of creatine phosphate to creatine in muscle contraction
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Where is creatine Kinase is located?
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-found mainly in the heart, skeletal muscle, and brain tissue
-damage to any these tissue will elevate the total CK |
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Creatine Kinase indications?
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-used to support diagnosis of myocardial injury
-may indicate neurological or skeletal muscle damage |
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CK Isoenzymes:
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MB: heart fraction 0%
MM: Skeletal muscle 100% BB: brain and lung 0% |
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CKMB and MI
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-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 |
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CKMB usually rises in..
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-unstable angina
-shock -malignant hyperthermia -myocarditis |
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CKMB does not usually rise in..
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-angina
-pulmonary embolism -CHF |
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What is used to avoid misdiagnosis of MI?
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-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 |
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CKMB is useful in...
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-quantifying degree of MI and timing the onset and appropriateness of thrombolytic therapy
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What causes a rise in AST and LD but not in CK?
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acute liver disease
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Total CK rises in...
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-moderate strenuous exercise
-distance running -weight lifting -DTs -seizures -surgery -delivery -hypothyroidism -hypokalemia |
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Total CK and hypothyroidism and hyopkalemia
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-elevated in 80% of pts with hypothyroidism or hypokalemia due to muslce damage
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Benefits of CK?
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-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) |
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Normal CK value is based on...
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patient size and muslce mass
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Is single value of CK useful?
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single value is of little value; need to look at trend over time
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CKMM is elevated in...
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-skeletal muslce injury
-hypoxia -exercise -seizure -inflammation -IM injection -hypothyroidism -hypocalcemia |
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When should CK measurements be taken?
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-admission
-4-6 hours -12 hours -18 hours -24 hours |
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What are Troponins?
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-proteins that exist in skeletal and cardiac muscle
-2 types: T and I |
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What do Troponins do?
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-help regulate muscle contraction
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How are cardiac specific troponins separated?
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-using monoclonal antibodies or ELISA techniques
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Troponin values:
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TN T <0.2 ng/ml
TN I < 0.3 ng/ml |
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Troponin elevation, peak, normalization times:
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Elevates: 2-6 hours
Peaks: 12-16 hours TN I normalizes: 7-10 days TN T normalizes: 10-14 days |
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TN vs CKMB
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-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) |
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So if TN I is so good, why bother with CKMB at all?
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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
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Disadvantages to Troponin?
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Not helpful for reinfarct
cannot tell if elevation is old or new |
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Indication for Troponin?
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-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 |
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What is Myoglobin?
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-oxygen binding protein found in cardiac and skeletal muslce
-NOT AN ENZYME!! |
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When is myoglobin test indicated?
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-early eval of pt with suspected MI (provides early index of damage to myocardium)
-dx disease or injury to skeletal muscle |
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when does Myoglobin elevate?
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rises: 0-3 hours
peaks: 6-8 hours normalizes: 20-36 hours |
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Myoglobin vs CK
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-myoglobin is more sensitive than CK isoenzymes but less specific (any trauma or injury may elevate myoglobin)
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Cardiac enzymes elevation comparison
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Myoglobin (0-3 hr)
Troponin (2-6 hr) CKMB/ CKtotal (3-6 hr) AST (8-12 hr) LDH (24-48 hr) |
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Cardiac enzymes normalization comparison
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CKMB (12-48 hr)
myoglobin (20-36 hrs) AST (3-8 days) LDH (5-10 days) Troponin I (7-10 days) |
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Cardiac enzymes specificity comparison
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troponin (cardiac injury ONLY)
CKMB AST/LDH |
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Cardiac enzymes sensitivity comparison
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myoglobin (most sensitive, BUT not enzyme)
Troponin CKMB LDH AST |
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Cardiac enzymes peak comparions
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?
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