Common Blood Chemistry Test 

What are blood chemistry tests?

• Tests performed on blood sample to measure the amount of certain analytes in our body
• involve electrolytes, proteins, enzymes, hormones, vitamins, minerals, lipids and glucose
• provide important information on the function of kidneys, liver, heart, and other organs
• used for screening and diagnosis of various human diseases, as well as treatment monitoring

Lipids (fats)

• organic, nonpolar compounds
• mainly composed of carbon-hydrogen (C-H) bonds (hydrocarbon chains)
• rich source of energy & storage for excess calories
• integral part of cell membrane
• protection & insulation
• <<precursors for steroid hormones, prostaglandins, leukotrienes & lipoxins<<

Fatty acids

• occur in esterified form (^^as building blocks for lipids^^), and free fatty acid form

• linear hydrocarbon chains with terminal carboxyl group (-COOH)

  

• amphipathic/amphiphilic molecule

• categorisation based on the length of hydrocarbon chain:

  • short-chain FA: ≤6 carbons
  • medium-chain FA: 8-12 carbons
  • long-chain FA: 14-18 carbons
  • very-long chain FA: ≥20 carbons

• most commonly found: palmitic acid (16C) & stearic acid (18C)

• categorisation based on the degree of saturation in the hydrocarbon chain:

  • saturated FA
  • unsaturated FA

Triglycerides (triacylglycerols)

• consists of ^^1 molecule of glycerol^^ esterified with ==3 fatty acids molecules==
• present in dietary fat; synthesised in the liver & adipose tissue

Cholesterol

• ==unsaturated== ==steroid alcohol==; amphipathic lipid (both hydrophilic and hydrophobic)
• almost exclusively synthesised by animals
• present in dietary fat; synthesised in liver
• precursor of steroid hormones & bile acids; does not serve as a source of energy fuel

Lipoproteins

• consists of a non-polar core triglycerides & cholesteryl esters

• surrounded by a polar surface layer of phospholipids, cholesterol, & apolipoproteins

• classification based on different density fractions after ultracentrifugation

  

• LDL - associated with increased risk of cardiovascular disease

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Lipids/Lipoproteins Analyses

Dyslipidemias

• diseases associated with abnormal lipid concentrations

• cause:

  • genetic abnormalities
  • environmental/lifestyle imbalances
  • secondary to other diseases

• defined by clinical characteristics & laboratory test results

• laboratory analyses:

  • total cholesterol
  • HDL
  • LDL
  • triglycerides

• clinical reference ranges for lipids

  

1. Cholesterol measurement

   • serum/plasma specimens are collected after fasting for at least 12 hours

   • serum/plasma specimens can be refrigerated at 4C for several days

     

2. HDL measurement

   • two-step procedure with manual pretreatment
   • precipitation reagent aggregates non-HDLs which are sedimented via centrifugation
   • HDL is then quantified by enzymatic assays

3. LDL measurement

   • via Friedewald calculation
   • total cholesterol, triglycerides and HDL are quantified
   • VLDL is estimated as [triglyceride level/5] in mg/dL unit
   • LDL = total cholesterol - HDL - VLDL

4. Triglyceride measurement

   • perform in conjunction with total cholesterol

   

Lipid Disorders

1. [[Arteriosclerosis[[

   • deposition of lipids (esterified cholesterol) in artery walls

   • results in fatty streaks → plaques (smooth muscle cells, extracellular lipid, calcification & fibrous tissue) → partial or complete occulsion of blood flow

   • LDL → initiate & promote plaque formation

     → every 1% decrease in LDL concentration leads to 2% decrease in arteriosclerosis risk

2. Hypercholesterolemia

   • associated with genetic abnormalities [i.e., familial hypercholesterolemia (FH)]
   • homozygotes
     • total cholesterol ~800-1000mg/dL (20-26 mmol/L)
     • first heart attack in teenage years
   • heterozygotes
     • ~300-600 mg/dL (8-15 mmol/L)
     • symptomatic for heart disease in 20s-50s

3. Hypertriglyceridemia

   • due to genetic abnormalities (e.g., FH)
   • consequence of secondary causes (e.g., hormonal abnormalities, diabetes mellitus or nephrosis)
   • imbalance between synthesis & clearance of VLDL
   • many coronary heart disease patients have moderately elevated triglycerides & decreased HLDL level

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Summary (Part 1)

• [ ] Different types of lipids
• [ ] Laboratory analyses for lipids/lipoproteins
• [ ] Development of arteriosclerosis

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Carbohydrates

• Large macromolecules containing C, H & O atoms

• Generic formula:

• Contain C=O and -OH functional groups

• Grouping based on the number of carbon:

  • trioses (3C)
  • tetroses (4C)
  • pentoses (5C)
  • hexoses (6C)

• Grouping based on the location of the C=O functional group

  • aldehyde group (O=CH-)

    

  • ketone group (O=C)

    

• Saccharide - basic unit structure

• Classification:

  • monosaccharide (e.g., glucose, fructose, galactose)
  • disaccharide (e.g., lactose, maltose, sucrose)
  • oligosaccharide (e.g., oligofructose, maltotriose)
  • polysaccharide (e.g., amylose, glycogen)

Glucose

• Major energy supply
• primarily stored as glycogen in liver & muscle
• disease states:
  • hyperglycaemia
  • hypoglycaemia

Hyperglycaemia

• hyper (high) + glykys (sweet/sugar) + haima (blood)
• an increase in blood glucose level
• defined as blood glucose level (>125mg/dL during fasting)
• Causes:
  • reduced insulin secretion
  • decreased glucose utilisation
  • increased glucose production
• Laboratory findings (blood specimen)
  • increased glucose level in plasma
  • increased serum osmolality
  • ketones in serum (ketonemia)
  • decreased blood pH (acidosis)
  • electrolyte imbalance

Diabetes Mellitus

• metabolic disorder characterised by chronic hyperglycemia

• arise from defects in the secretion, or action of insulin, or both

• clinically defined as high plasma glucose concentrations at which there is an increased risk of retinopathy, nephropathy & neuropathy

• type 1 diabetes mellitus

  • pancreatic islet B-cell destruction
  • tendency to ketoacidosis

• type 2 diabetes mellitus

  • insulin resistance
  • insulin secretory defect

• gestational diabetes mellitus

  • glucose intolerance
  • metabolic & hormonal changes during pregnancy

• Laboratory diagnosis

  

  • measurement of glycated haemoglobin

  • ‘time-weighted’ average plasma glucose concentration over the past 2-3 months

  • in vivo glycation of haemoglobin is proportional to plasma glucose concetration

  • average plasma glucose concentration during the last 30 days accounts for 50% of the HBAlc concentration (glycated haemoglobin)

  • expressed as a proportion of total haemoglobin (in percentage)

    

• Prediabetes

  • higher than normal blood glucose level, but insufficiently high to be considered as diabetes
  • increased risk of type 2 diabetes mellitus, heart disease & stroke
  • <<reversible<<
  • criteria:
  • 126mg/dL > fasting glucose level ≥ 100 mg/dL
  • 200mg/dL > 2hr OGTT level ≥ 140 mg/dL
  • HBAlc concentration of 5.7-6.4%

Glucose Assay

• serum/plasma sample
• enzymatic approach - glucose oxidase, hexokinase, glucose dehydrogenase
• generate measurable coloured product proportional to glucose concentration

Glucometer

• medical device for point-of-care measurement of blood glucose concentration
• rapid & easy home-based blood glucose monitoring, particularly among individuals with Type 1, 2 & gestational diabetes mellitus
• requires only a small amount of blood sample (from fingertip)

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Hypoglycaemia

• Blood glucose level is lower than the standard range
• fasting blood sugar ≤ 70 mg/dL or 3.9 mmol/L
• common among
  • particularly in type 1 diabetic patients
  • type 2 diabetic patients who are on insulin/medication
• rare in individuals with normal glucose metabolism
  • diagnosis should be made only if the individual demonstrates:
  • hypoglycaemic symptoms
  • low plasma glucose concentration <50 mg/dL
  • symptoms are relieved by administering glucose/glucagon

Gestational Diabetes Mellitus

• Recommendation: all nondiabetic pregnant women should be screened at 24-28 weeks of gestation

• one-step approach: 2-hr oral glucose tolerance test (OGTT) by using 75g glucose load

• requires overnight fasting of at least 8hr

  

==Complete Blood Count==

• to evaluate overall health
• to screen, diagnose & monitor certain health disorders, e.g., anaemia, infection & leukemia
• Measurement and/or counting of:
  • red blood cells
  • white blood cells
  • haemoglobin
  • haematocrit
  • platelets
  • mean corpuscular volume (MCV)

Red Blood Cells

• measure the number of red blood cells, which carry oxygen from the lungs to the rest of our body
• normal count (male):
  • 4.35-5.65 million cells/ul
• normal count (female):
  • 3.92-5.13 million cells/ul
• increased level may indicate:
  • polycythemia
  • respiratory distress
  • high altitude
• decreased level may be a sign of:
  • iron anemia
  • vitamin B12, vitamin B6 and/or folic acid anaemia
  • haemorrhage
  • liver & renal dysfunction

White Blood Cells

• measure the total number of WBCs (without differential)

• measure the number of each of the 5 basic white blood cell types (differential)

  • neutrophils, eosinophils, basophils, lymphocytes & monocytes
  • expressed as percentage or absolute value

• elevated white blood cells count may indicate inflammation or infection

  

• low cells count may indicate autoimmune diseases, bone marrow disorders or cancers

• normal: 3.49-9.6 billion cell/litre

Haemoglobin

• protein that carries oxygen in the red blood cells
• normal (male): 132-166 g/L
• normal (female): 116-150 g/L
• increased level may indicate dehydration, emphysema, asthma, polycythemia
• decreased level may indicate iron deficiency anaemia, microscopic internal bleeding, digestive inflammation

Hematocrit

• known as packed cell volume
• percentage of the total occupied by packed red blood cells when a given volume of whole blood is centrifuged
• normal (male): 38.3% - 48.6%
• normal (female): 35.5% - 44.9%
• abnormal value indicates the similar clinical conditions as haemoglobin

Platelets

• responsible for blood coagulation and vascular integrity
• reference (male): 135-317 billion/L
• reference (female): 157-361 billion/L
• increased level: atherosclerosis, rheumatoid/inflammatory arthiritis, certain cancers
• decreased level: idiopathic thrombocytopenia, blood loss

Means Corpuscular Volume (MCV)

• the volume in cubic microns occupied by an average single red blood cell
• ↑ level (macrocytic RBCs): vitamin B12/folic acid anaemia, dehydration
• ↓ level (microcytic RBCs): iron anaemia, microscopic internal bleeding
• other RBCs-related markers:
  • MCH (mean corpuscular haemoglobin)
  • MCHC (mean corpuscular haemoglobin concentration)

Summary (Part 2)

• [ ] Hyperglycaemia and hypoglycaemia
• [ ] complete blood count & its clinical indications

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