Biochemistry

Question 1

Biomedical tests for DM

Answer 1

1. Urinary glucose level
   - only for glycosuria
   - only reflect level during formation of urine (NOT testing time)
2. Glucose tolerance test
   - in the morning (diurnal rhythm: higher in morning, lower in afternoon)
   - fasting glucose (blood/urine) as baseline
   - drink glucose dose 1.75g/kg
   - blood/urine collected every 2 hours
   - withhold non-essential drugs
   - must fast for at least 8 hours
   - fever can produce diabetic response in OGTT
   - no alcohol

Definition of DM:

1. Symptoms of DM + plasma glucose > 11.1 mmol/L
2. Fasting plasma glucose > 7 mmol/L
3. OGTT 2 hour plasma glucose > 11.1 mmol/L

Question 2

Normal pH of blood

Answer 2

7.35-7.45

Critical value: 6.9, 7.8

Question 3

Acid base balance

Answer 3

Metabolic component: HCO3
Acidic component: pCO2

[H] proportional to pCO2/[HCO3]

Respiratory acidosis: pCO2 ↑, HCO3 may also ↑ (trying to compensate)
Metabolic acidosis: [HCO3] ↓, pCO2 may also ↓ (trying to compensate)
Mixed acidosis: [HCO3] ↓, pCO2 ↑

Respiratory alkalosis: pCO2 ↓, HCO3 may also ↓ (trying to compensate)
Metabolic alkalosis: [HCO3] ↑, pCO2 may also ↑ (trying to compensate)
Mixed alkalosis: [HCO3] ↑, pCO2 ↓

Question 4

Base excess

Answer 4

Express non-respiratory pH disturbance (metabolic pH disturbance)

Excess base in ECF remains constant during acute changes in pCO2 —> reflects only non-respiratory component of pH disturbance

***[titratable base] - [titratable acid] when titrating average ECF to an arterial plasma pH of 7.4 at pCO2 = 40 mmHg at 37oC

Normal: -2 to +2 mEq/L
>+2: excess HCO3 —> metabolic alkalosis
metabolic acidosis

Question 5

Anion gap

Answer 5

[Na] - [Cl] - [HCO3]

Value out normal range indicate presence of other ions e.g. lactate, sulphate, acetoacetate (there are contributions of other anions to the gape)

Base deficit + elevated anion gap = addition of acid
Base deficit + normal anion gap = HCO3 loss (HCO3 is exchanged for Cl —> anion gap no change)

Question 6

Separation of lipoprotein

Answer 6

Density: Chylomicron (最面) < VLDL < IDL < LDL < HDL (最底)

Electrophoresis: more lipoprotein —> more negative charge —> move towards positive electrode more
Chylomicron < LDL < VLDL < HDL (最遠)

Question 7

Full lipid profile, fasting lipoprotein profile, non-fasting lipoprotein profile

Answer 7

Full:

1. Total cholesterol
2. TAG
3. HDL-C

Fasting:

1. Total cholesterol
2. TAG
3. LDL-C
4. HDL-C

Non-fasting:

1. Total cholesterol
2. HDL-C

Question 8

Myoglobin, CKMB, Troponin

Answer 8

Myoglobin:

• non-cardiac specific
• rapidly return to normal

CKMB:

• high concentration in heart, some in skeletal muscle
• rapid release, sustain for a few days, useful when patients come some time later
• convenient and fast

Troponin: (Thin filament = Actin + Troponin + Tropomyosin)
- Troponin T (biphasic, 3-4 hours, 10 hours to a few days)
—> bind to tropomyosin
- Troponin I (single peak, 4 hours, peak 14-18 hours, 5-7 days)
—> bind to actin
—> inhibit actin-myosin binding until Ca bind Troponin C
—> no cross interference from skeletal muscle activity
- Troponin C
—> bind Ca to expose binding site

***Any Troponin level > upper reference limit at 99th percentile = Myocardial damage
To confirm MI: Troponin T + Troponin I + CKMB
2 markers is suggested for routine AMI detection: one early and one definite

AST: liver function test
LDH: non-specific
BNP: produced by cardiac muscle (related to tension on cardiac muscle, useful to detect strain)