Lab Med Flashcards
Acute MI
imbalance b/w myocardial O2 supply (ischemia) and demand, resulting in injury to and the eventual death of myocytes
myocardial necrosis is most often associated with what?
- a thrombotic occlusion superimposed on coronary atherosclerosis
- the process of plaque rupture and thrombosis is one of the ways in which coronary atherosclerosis progresses
STEMI
-total occlusion of coronary blood flow = ST elevation
NSTEMI
partial occlusion of coronary blood flow = no ST elevation (could show ischemia as ST depression)
What does the absence of blood flow lead to?
- cardias muscle tissue death
- spilling cardiac biomarkers into the circulatory system
How often is the initial EKG diagnostic for AMI?
-about 30% of patients
When is troponin testing most useful?
when patients are having nondiagnostic EKG tracings
Troponin (cTnI or cTnT)
cardiac regulatory proteins specific to the myocardium that control the Ca++-mediated interaction b/w action and myosin
Troponin is the perferred test for the diagnosis of what?
ACS
troponin establishes the diagnosis of what?
irreversible myocardial necrosis, even when EKG changes are non diagnostic
What is important to know about an elevated troponin?
several distinct pathologies may cause it to be elevated, not all of them involve myocyte necrosis
How is NSTEMI strictly defined in terms of lab values?
-a rise and fall in serum biomarkers (usually troponin) exceeding the 99th percentile of a normal reference population
Time it takes for troponin levels to rise
- 3-6 hrs after onset of ischemic symptoms
- can be delayed from 8-12 hrs
Why is it important to know that troponin levels could be delayed in rising?
need to get serial troponin levels
Why is troponin most useful in NSTEMI
CK-MB and myoglobin are not useful in the diagnosis of ACS w/ mild ischemia w/o necrosis
CK-MB is more relevant to use with what condition?
STEMI
CK-MB levels time to rise
-3-4 hrs after onset of myocardial injury
myoglobin
- early marker for myocardial necrosis
- increases 2 hrs after onset of necrosis
What is the recommendation for when a pt has negative biomarkers w/i 6 hrs of onset of sx?
remeasure 8-12 hrs after onset
What other reasons could CK-MB be elevated?
- MANY (not listing all from lecture)
- necrosis or inflammation of cardiac muscle
- necrosis, inflammation or acute atrophy of striated muscle
- endocrine disorders
- some infections
explain why CK-MB detects muscle problems
-CK (creatine kinase) is an enzyme that controls energy flow within muscle cells
in addition to everything listed that can cause CK-MB to increase, what can cause CK to increase?
she emphasized rhabdomyolysis but there are many more
additional sxs of CHF
- 2-3+ bipedal edema
- b/l diffuse course rales on ausculation
BNP (brain natriuretic peptide)
-a hormone secreted by myocytes in the left ventricle in response to pressure overload/myocyte stretch
what effects does BNP cause
- diuretic
- natriuretic
- vascular smooth muscle relaxation
In what conditions can BNP be increased?
- heart failure
- left vent. dysfunction
- renal impairment
- CAD
- valvular dz
- arrhythmias
- brain injury
- anemia
- sepsis/shock
What is BNP used for?
- screening and diagnosis of CHF
- prognosis of heart failure
what is the correlation of BNP and prognosis of heart failure?
the higher the BNP, the worse the outcome (same in AMI)
D-dimer is a test to rule out what?
- aortic dissection
- PE
- DVT
D-dimer ELISA use for PE
in pts w/ low pretest probability:
-can rule out PE if it is negative (high NPV)
when is d-dimer ELISA not helpful?
- if positive (low PPV)
- if pretest probability is intermediate or high
PT (prothrombin time)
-assesses the coagulation activity of the extrinsic and common coagulation pathways
PTT (partial thromboplastin)
-thromboplastin is potent activator of coag system
Use of PT/INR and PTT
- eval of clotting disorders
- eval of liver function
- monitor long term oral anticoag therapy (coumadin)
what is the preferred reporting to monintor pts on vit. K antagonist therapy?
- INR
- (in all other cases PT)
market prolongation of the PT in liver dz indicates?
advanced dz
market elevation of INR in pts using vit. K antagonists is a marker of what?
excessive anticoagulation
INR below 2 reflects what?
insuffiecient anticoagulation
In what 2 circumstances is combined abnormal PT and PTT found?
- medical: admin of oral anticoags, DIC, liver dz, vit. K deficiency, massive transfusions
- coag factor abnormalities
What all is included in a lipid panel?
- total cholesterol
- LDL
- HDL
- triglycerides
cholesterol
- steroid carried in the bloodstream as a lipoprotein
- necessary for cell membrane functioning
- precursor to bile acids, progesterone, vit. D, estrogens, glucocorticoids and mineralocorticoids
total cholesterol level
-desirable level that puts a person at a lower risk of coronary heart dz
LDL
- produced in the metabolism of VLDL
- carry cholesterol in the bloodstream from the liver to the peripheral tissues
- “bad cholesterol”
LDL levels are associated w/ what?
- atherosclerosis
- coronary heart dz
LDL is increased in what conditions?
- familial hypercholesterolemia
- nephrotic syndrome
- hepatic dz or obstruction
- chronic renal failure
- DM
- hyperlipidemia
LDL is decreased in what conditions?
- a-betalipoproteinemia
- hyperthyroidism
- tangier dz
- hypolipoproteinemia
- chronic anemia
- Apo C-II deficiency
- hyperlipidemia type I
when do you measure LDL values?
fasting
What extrinsic factors could reduce LDL?
- stress
- recent illness
- estrogens
What extrinsic factors could increase LDL?
- cigs
- HTN
- fam hx
HDL
- produced by liver
- carries cholesterol in the blood from tissues to the liver (reverse transport)
- “good cholesterol”
how are HDL levels related to CHD
- inversely
- it is an independent risk factor
concentrations of HDL and triglycerides associated w/ certain disorders
- 250-500: peripheral vascular dz
- > 500: panreatitis risk
- > 1000: hyperlipidemia
- > 5000: eruptive xanthoma, corneal arcus, lipemia retinalis, enlarged liver and spleen
triglycerides
- form of fat and major source of energy for the body
- stored in adipose
- move via blood from gut to adipose
- play important role in metabolism and transport
review
case study at end of lecture
