SH

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

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