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

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

Summary (Part 1)

• Different types of lipids

• Laboratory analyses for lipids/lipoproteins

• Development of arteriosclerosis

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)

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