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Biochemistry II > Chapter 66: Organ Function Tests > Flashcards

Chapter 66: Organ Function Tests Flashcards

1
Q

Organ function tests (definition)

A
  • Collective term for a variety of tests/procedures that evaluate organ function
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2
Q

Primary uses of OFTs

A
  • Detecting disease (less useful in detecting cause)
  • Monitor response to treatment/assess prognosis
  • Part of the diagnostics
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3
Q

Shotgun approach

A
  • Using numerous OFTs

- Confuses the investigation

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4
Q

Organ disease be suspected when

A
  • Results of at least two biochemically or physiologically independent tests generate abnormal results
  • Compare results with reference range
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5
Q

Idea OFT (though rarely available in routine practice)

A
  • Correct result (accuracy) that is the same if repeated (precision)
  • Measures low concentrations of the analyte (sensitivity)
  • Not subject to interference by other substances (specificity)
  • Should be cheap, simple and quick to perform readily automated
  • Painless to patient, free of risk
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6
Q

Specificity

A
  • Probability that an OFT returns negative results and person is actually negative
  • High specificity = less false positives
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7
Q

Sensitivity

A
  • Proportion of true positives detected by the organ function test
  • High sensitivity = less false negatives
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8
Q

Kidney functions

A
  • Remove metabolic waste
  • Water balance
  • Maintain body fluid pH
  • Excrete toxins/metabolites
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9
Q

Rate of glomerular filtration

A
  • 130 mL/min

- (125 mL/min for physio)

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10
Q

Main types of kidney function tests

A
  • Blood (plasma creatinine, BUN)
  • Urinalysis
  • Glomerular filtration rate (inulin, creatinine)
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11
Q

Plasma creatinine evaluates

A
  • Muscle turnover
  • Abnormal men > 2.0 mg/dL
  • Abnormal women > 1.5 mg/dL
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12
Q

Healthy kidney filtration

A
  • 30mg/L of protein (minimal in urine)

- 24 hour collection should contain no more than 150 mg of protein

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13
Q

Proteinuria

A
  • Presence of significant amounts of protein in the urine

- Indicates renal disease/glomerular damage

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14
Q

Urinalysis (often first requested)

A
  • Small sample or 24 hour collection
  • Can reveal systemic issues too
  • Complement w/ micro examination of sediment
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15
Q

Urine collected for urinalysis should NOT contain

A
  • Glucose
  • Proteins
  • Hemoglobin
  • Metabolites
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16
Q

Urinalysis ideal pH

A
  • Acidic (5.0-6.0)
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17
Q

Plasma creatinine

A
  • Endogenous, derived from muscle tissue
  • Preferred test of kidney function
  • More specific than BUN
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18
Q

Plasma creatinine production is dependent on

A
  • Muscle mass
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19
Q

Plasma creatinine removal from circulation

A
  • Filtered by glomerulus

- Some secreted into filtrate by the proximal tubule (elevated if GFR falls)

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20
Q

Plasma creatinine normal range

A
  • Men: 0.8 – 1.2mg/dL

- Women: 0.6 – 0.9mg/dL (lower during pregnancy and in children)

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21
Q

Elevated creatinine indicates impaired kidney function when

A
  • It’s not filtered

- Decline in GFR

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22
Q

Factors affecting accuracy of plasma creatinine

A
  • Obesity
  • Oedema
  • Pregnancy
  • Ascites
23
Q

Blood urea nitrogen (BUN) measures

A
  • Amount of nitrogen in the urea
  • Often performed alongside plasma creatinine
  • May be used to predict pancreatitis
24
Q

Urea (mwt 60D)

A
  • Relatively nontoxic waste product
  • Produced in liver (breakdown of excess dietary protein/urea cycle)
  • Filtered and excreted
25
Q

BUN reference range

A
  • 7-20 mg/dL
26
Q

BUN/kidney function relationship

A
  • As function decreases, BUN increases

- BUN elevated when renal function drops to 24-50% of normal

27
Q

A low BUN may be due to

A
  • Lack of protein
  • Severe liver disease
  • Overhydration
28
Q

Creatinine clearance values (normal 24 hour collection)

A
  • 90 - 139 ml/min men under 40
  • 80 - 125 ml/min women under 40
  • For people over 40, values decrease by 6.5 ml/min for each decade of life
29
Q

When GFR drops below 30 ml/min,

A
  • Tubular secretion can exceed the amount filtered at the glomerulus
30
Q

Liver function tests

A
  • Evaluate excretory or synthetic functions
  • Plasma assay of bilirubin
  • Prothrombin time/albumin
31
Q

Enzyme assays for liver function

A
  • ALT
  • AST
  • AP
  • CGT
32
Q

AST leaks from injured

A
  • Liver
  • Heart
  • Skeletal muscle
  • Erythrocytes (less often kidney)
33
Q

ALT is more specific for

A
  • Liver (but less stable in blood samples)
34
Q

AST and ALT generally follow the same upward/downward courses in liver disease

A
  • ALT rises less in alcoholism

- If ALT is greater than 300, suggests underlying problem is not alcoholism

35
Q

AST/ALT > 2

A
  • Indicates alcoholism
36
Q

Bilirubin

A
  • Breakdown product of hemoglobin
  • Normal levels usually below 1 mg/dL (majority unconjugated)
  • A variety of drugs may increase bilirubin
37
Q

Assay of bilirubin based on

A
  • Van den Bergh reaction
38
Q

Jaundice is caused by

A
  • Excess circulating bilirubin (> 2.5mg/dL)
39
Q

Elevated levels of unconjugated BR

A
  • Liver cell problems

- Kernicterus

40
Q

Elevated levels of conjugated BR

A
  • Obstruction either within the liver (intrahepatic) or outside the liver
41
Q

Ven den Bergh DIRECT reaction

A
  • Direct bilirubin measurement

- Conjugated bilirubin can be expressed as direct bilirubin (readily assayed with azo dyes)

42
Q

Direct bilirubin reaction

A
  • Water-soluble reagent (diazotized sulfanilic acid) reacts with conjugated bilirubin
  • Forms azobilirubin
  • Colorimetric assay at 600nm
43
Q

Normal direct bilirubin assay

A
  • Trace amounts of conjugated (direct) bilirubin

- Elevations of water soluble, conjugated bilirubin leads to increased levels in the urine

44
Q

Van den Bergh INDIRECT reaction

A
  • Additional accelerator agent added to free unconjugated bilirubin from serum albumin
  • Measures indirect or unconjugated bilirubin
45
Q

Normal indirect bilirubin assay

A
  • Normal values vary with age

- Elevated unconjugated bilirubin (high affinity for membrane lipids) leads to impairment of cell membrane function

46
Q

Analysis of blood ammonia may be useful in diagnosis/management of

A
  • Severe liver diseases
  • Hepatic encephalopathy
  • Liver failure
  • Heart failure
  • Hemolytic disease
47
Q

Measurement of blood ammonia levels are used to confirm a diagnosis of

A
  • Reye’s syndrome

- Together with the AST and ALT results

48
Q

Normal values for ammonia

A
  • Vary widely

- Depends on laboratory, patient age, and type of specimen

49
Q

Tests of cardiac function

A
  • Creatine kinase
  • Troponin T and I
  • C-reactive protein (CRP)
  • Myoglobin
  • B-type natriuretic peptide (BNP)
50
Q

C-reactive protein (CRP)

A
  • A crude hepatic marker of chronic inflammation

- Elevated in atherosclerosis

51
Q

Possible causes of elevated CRP

A
  • Genes connected with metabolic syndrome
  • Can also be used to predict MI or stroke
  • Often used in combination with CK-MB and cTnT
52
Q

Elevated myoglobin

A
  • Detected in plasma and urine

- Indicative of cardiac function

53
Q

B-type natriuretic peptide (BNP) assay

A
  • Used if congestive heart failure is suspected
54
Q

Routine urinalysis allows for determination of

A
  • Physical, chemical and microscopic properties of urine

Biochemistry II (5 decks)

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