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YEAR 5: Chemical Pathology AS > ChemPath: Enzymes and Cardiac Markers > Flashcards

ChemPath: Enzymes and Cardiac Markers Flashcards

1
Q

Where are most enzymes found?

A

Intracellularly

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2
Q

Why might serum enzymes be elevated?

A
  • infection
  • immune mediated/ inflammation- T1DM/ RA
  • ischaemia- MI, stroke, ischaemic colitis/ hepatitis
  • inherited
  • trauma
  • toxins- medications, rec drugs
  • tumour
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3
Q

What are the two types of intracellular enzymes?

A
  • Cytosolic
  • Subcellular (within organelles)
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4
Q

Describe the order of release of intracellular enzymes when cells are damaged.

A

Cytosolic are released first, followed by subcellular

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5
Q

In which tissues is ALP present in high concentration?

A
  • Liver- intrahepatic/ extrahepatic BDs
  • Bone
  • Intestines
  • Placenta
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6
Q

What is an increase in bone ALP caused by?

A

Increased osteoblast activity

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7
Q

What technique is used to separate isoenzymes?

A

Electrophoresis

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8
Q

List some physiological causes of high ALP.

A
  • Pregnancy - 3rd trimester (from placenta)
  • Childhood - growth spurt
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9
Q

List some causes of very high ALP (>5 x upper limit of normal).

A
  • Bone - Paget’s disease, osteomalacia, renal osteodystrophy, rickets
  • Liver - cholestasis, cirrhosis
  • Germ cell tumours
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10
Q

List some causes of moderately raised ALP (< 5 x upper limit of normal).

A
  • Bone - tumours, fractures, osteomyelitis
  • Liver - infiltrative disease, hepatitis
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11
Q

Difference between ALT and AST

A

ALT more specific to liver as higher there but AST found in liver, heart, kidneys

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12
Q

Causes of raised ALT- alanine transaminase

A

hepatic: toxins (alcohol/ paracetamol OD), hepatitis, NAFL, cancer, ischaemia

not used for kidney, pancreatitis or MI diagnosis

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13
Q

Why might GGT be elevated?

A

hepatobiliary: hepatitis, alcoholic liver, cholestatic

enzyme induction: alcoholics, rifampicin, phenytoin, phenobarbitone

pancreas: pancreatitis but better markers

kidney can affect too

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14
Q

Why might lactate dehydrogenase be elevated?

A

found in tissues without mitochondria (anaerobic resp)

WBC: lymphoma

RBC: haemolysis

placenta: germ-cell testicular cancer - seminoma

skeletal muscle: myositis

can be in cardiac and liver injury

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15
Q

Describe the ALP levels in osteoporosis.

A

It is NORMAL unless there is a fracture.

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16
Q

Which markers are used in acute pancreatitis?

A

Amylase

Lipase

17
Q

Where else is amylase found?

A

Salivary glands

NOTE: will be raised in parotitis

18
Q

why might serum amylase be elevated?

A
  • acute pancreatitis, perforated duodenal ulcer, bowel obstruction
  • stones/ infection in salivary gland
  • macro-amylase (amylase bound to Ig- benign, can do electrophoresis)
19
Q

What are the three forms of creatine kinase?

A
  • CK-MM = skeletal muscle
  • CK-BB = brain
  • CK-MB = cardiac muscle
20
Q

Describe the manifestations of statin-related myopathy.

A

Can range from myalgia to rhabdomyolysis

21
Q

List some risk factors for statin-related myopathy.

A
  • Polypharmacy (in particular, fibrates and cyclosporin and other drugs metabolised by CYP3A4)
  • High dose
  • Genetic predisposition
  • Previous history of myopathy with another statin
  • Vitamin D deficiency (increased risk of statin intolerance)
22
Q

List some other causes of high CK.

A
  • Muscle damage
  • Myopathy (e.g. Duchenne muscular dystrophy)
  • Polymyositis, dermatomyositis
  • MI
  • Severe exercise
  • Physiological (Afro-Caribbeans)
23
Q

What are two other uses of enzymes in clinical medicine?

A
  • Markers of therapeutic response and drug toxicity (e.g. TPMT activity should be measured before starting thiopurines (e.g. azathioprine))
  • Reagents to measure other substances (e.g. glucose oxidase is used to measure plasma glucose)
24
Q

List three cardiac enzymes that used to be used as markers of cardiac damage.

A

CK

AST

LDH

25
Q

Where are myoglobins found within cells?

A

Cytosol

26
Q

Where is CK-MB found within cells?

A

Within the mitochondira and nucleus

27
Q

Where are troponins found within cells?

A

Within the contractile apparatus

NOTE: there is also a free cytosolic pool of troponins

28
Q

What factors affect troponin result?

A

age

gender

acute or chronic kidney disease

number of myocytes injured

29
Q

Causes of elevated cardiac troponin I

A

primary cardiac injury:

  • ACS: STEMI/ NSTEMI, angina
  • myocarditis
  • cardiomyopathy
  • aortic dissection

secondary cardiac injury:

  • PE
  • systemic infection
  • anaemia - upper GI bleed
30
Q

Describe how troponin levels change with time following an MI.

A
  • Rise at 2-4-6 hours post-MI
  • Peaks at 12-24 hours
  • Remains elevated for 3-10 days
  • So, troponins should be measured at 6 hours and 12 hours after the onset of chest pain in a suspected MI- >50% increase= ACS
31
Q

Outline the diagnostic criteria for MI.

A

Typical rise and gradual fall in troponin or more rapid rise and fall in CK-MB with at least one of the following:

  • Ischaemic symptoms
  • Pathological Q waves
  • ECG changes suggestive of ischaemia
  • Coronary artery intervention

Pathological findings of acute MI

32
Q

How are biomarkers used when deciding whether to thrombolyse?

A

None of the current biomarkers rise quickly enough to aid decisions regarding thrombolysis (so it is based on clinical findings and ECG)

33
Q

What are the main biomarkers used in cardiac failure?

A
  • ANP - from the atria
  • BNP - from the ventricles
  • BNP is used to assess ventricular function and can be used to exclude heart failure (high negative predictive value)
34
Q

When is BNP released?

A

in response to cardiac overload or muscle stretch

35
Q

How is BNP produced?

A

from NPPB gene which produces a molecule which is cleaved into NT-proBNP and BNP, which is biologically active

blood tests usually measure NT-proBNP as half life 3 hours but BNP can be measured in hospital

36
Q

What drug can falsely increase BNP?

A

Entresto contains a neprolysin inhibitor which stops break down of BNP, leading to higher levels so NT-proBNP measured instead

37
Q

Define 1 international unit of enzyme activity.

A
  • Quantity of enzyme required to catalyse a reaction of 1 µmol of substrate per minute

NOTE: activity is affected by assay conditions such as pH and temperature (so reference ranges may differ between laboratories)

38
Q

How can BNP be used in heart failure diagnosis?

A

ruling out HF + assess long-term prognosis but echo and clinical judgement needed for diagnosis

YEAR 5: Chemical Pathology AS (27 decks)

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