AN INTRODUCTION TO LABORATORY TESTS

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AN INTRODUCTION TO LABORATORY TESTS
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AN INTRODUCTION TO LABORATORY TESTS

• Aim - introduction to laboratory tests of
  clinical and diagnostic importance - biochemistry
  and haematology
• Use?
• Assist doctor in making a diagnosis and
  monitoring treatment
• Assist pharmacist in assessing and monitoring
  drug treatment
• Individual tests may provide insufficient
  information - consider pattern of tests within a
  group
• Single tests are of less value than a series -
  show trends
• Expressed as a reference range - based on the
  assumption that 95 of the population are normal

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REFERENCE VALUES
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1. RENAL FUNCTION TESTS

• Serum Creatinine, Creatinine Clearance, Urea
• Used to give an estimate of glomerular filtration
  rate (GFR)
• GFR gives an indication of the efficiency of the
  kidney and is decreased in renal impairment
• In practice, this is crucial information to
  determine drug handling. Renally cleared drugs
  and metabolites will accumulate in renal
  impairment
• Some drugs may reduce GFR e.g. NSAIDs and
  aminoglycosides

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1. RENAL FUNCTION TESTS

• Serum Creatinine (Cr)
• Reference range 80 -150 micromoles/L
• Creatinine is a major metabolite of creatine
  phosphate, a major constituent of muscle.
• Excreted almost exclusively by glomerular
  filtration freely filtered.
• GFR results in creatinine
• Creatinine Clearance (CrCl)
• Renal impairment iflt 50ml/min
• Serum creatinine can be used in the
• Cockroft-Gault equation to estimate creatinine
  clearance. GFR approximates to CrCl

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COCKROFT and GAULT EQUATION

• Cr Cl (140 - age) x Wt (kg) x F
• Cr
• Units are mls/minute
• Cr serum creatinine in micromoles/litre
• F 1.23 for males, 1.04 for females

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1. RENAL FUNCTION TESTS

• Urea (4.2-6.4mmol/L)
• Also known as blood urea nitrogen, BUN.
• Used to estimate renal function, but poor measure
  of minor degrees of renal impairment as it is
  influenced by other factors.
• End product of protein metabolism. (High protein
  diet increases urea)
• Usually measured as urea and electrolytes (UEs)

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1. RENAL FUNCTION TESTS

• HIGH SERUM CREATININE
• signifies
• GFR
• Renal impairment

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RENAL IMPAIRMENT
Grade GFR (Creatinine Clearance) ml/min Serum Creatinine micromoles/L
Mild 20-50 150-300
Moderate 10-20 300-700
Severe lt10 gt700

• Renal impairment is arbitrarily divided into 3
  grades ( see BNF)
• Glomerular Filtration rate, measured by
  creatinine clearance
• Note - definitions vary. Consult product
  literature for specific drugs

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2. ELECTROLYTES

• Sodium, potassium, calcium, phosphate,
• glucose
• Sodium
• Main extracellular cation. Osmolality of ECF is
  largely determined by sodium and associated
  anions
• Intimately linked with distribution of water
  between intra and extracellular compartments (ICF
  and ECF). Reflects fluid status of patient
• Changes in body sodium content result in changes
  in ECF volume
• Reference value 133-144mmol/L

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2. ELECTROLYTESTOTAL BODY WATER
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2. ELECTROLYTESINTRA and EXTRA CELLULAR FLUID
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2. ELECTROLYTES

• Hyponatraemia
• Indicates an increase in free water in
• ECF
• Caused by
• Sodium (and water) loss e.g.diuretics
• Water retention in excess of sodium e.g.
  carbamazepine, tricylclics
• Symptoms if Nalt120mmol/L headache, nausea,
  cramps, confusion

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2. ELECTROLYTES

• Hypernatraemia
• Indicates a loss of free water and an increase in
  sodium
• Caused by
• Excessive water loss, or combined loss of water
  and sodium with predominant water loss e.g.
  diarrhoea in infants
• Unlikely to be caused by sodium excess - thirst
  compensates
• Symptoms at Nagt160mmol/L - thirst, mental
  confusion coma

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2. ELECTROLYTES

• Potassium
• Principal intracellular cation (lt2-3 in ECF)
• Involved in muscle excitation and cardiac
  function. Body sensitive to changes in serum
  potassium.
• Reference values 3.5 - 5 mmol/L
• Hypo - reduced muscle activity, arrhythmias,
  mental slowing.
• Hyper - ventricular fibrillation and cardiac
  arrest.

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2. ELECTROLYTES

• Hypokalaemia
• Decreased potassium
• Serious at lt2.5mmol/L
• (reference range 3.5-5)
• Caused by
• Diuretics (loop and thiazide)
• Loss from GI tract (diarrhoea, vomiting)
• Shift into cells (insulin, salbutamol)

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2. ELECTROLYTES

• Hyperkalaemia
• Increased potassium
• Serious at gt6.5 mmol/L
• (reference range 3.5-5)
• Caused by
• Potassium sparing diuretics
• Acute renal failure
• Catabolic states e.g. diabetic ketoacidosis
• Vast intracellular damage cell lysis, release
  of K

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3. LIVER FUNCTION TESTS

• No specific test to determine degree of liver
  impairment
• Important to look for a pattern using the
  following tests
• ALP
• AST and ALT
• GGT
• Bilirubin

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3. LIVER FUNCTION TESTS

• Alkaline Phosphatase (ALP)
• Found in cells lining the bile duct rise
  usually signifies cholestasis c (obstruction to
  flow in bile duct)
• Aspartate aminotransferase (AST) and
• Alanine aminotransferase (ALT)
• Found in hepatocytes rise usually signifies
  hepatocellular damage h
• Gamma-glutamyl transferase (GGT)
• Synthesis of the enzyme induced by alcohol and
  drugs. Rise usually signifies hepatobiliary
  disease hb

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3. LIVER FUNCTION TESTS

• Bilirubin
• Breakdown product of haemoglobin
• Rise in UNCONJUGATED form usually signifies
• haemolysis (increased RBC destruction), or
• direct hepatocellualr damage.
• Rise in CONGUGATED form usually signifies
• cholestasis - obstruction to bile flow
• A rise in both CONJUGATED UNCONJUGATED
  bilirubin suggests
• mixed hepatocellular damage and cholestasis.
• Changes in LFTs may be due to disease process
  (e.g. gallstones, hepatitis) or due to drugs
• (e.g. chlorpromazine h,c, flucloxacillin c).

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3. LIVER FUNCTION TESTSBILIRUBIN and UROBILINOGEN