PRE-ANALYTICAL PHASE

• Diurnal variation


  Fluctuations in the levels of certain substances in the body over the course of a day
• Substances affected by diurnal variation

  • Cortisol
  • Adrenocorticotropic hormone
  • Plasma renin activity
  • Aldosterone
  • Insulin
  • Growth Hormone
  • Acid Phosphatase
  • Thyroxine
  • Prolactin
  • Iron
  • Calcium
• Cortisol


  Peaks 4–6 AM; lowest 8 PM–12 AM; 50% lower at 8 PM than at 8 AM; increased with stress
• Adrenocorticotropic hormone


  Lower at night; increased with stress
• Plasma renin activity


  Lower at night; higher when standing than supine
• Plasma renin activity


  Higher when standing than when supine
• Aldosterone


  Lower at night
• Insulin


  Lower at night
• Growth Hormone & Acid Phosphatase


  Higher in afternoon and evening
• Thyroxine


  Increases with exercise
• Prolactin


  Higher with stress; higher levels at 4 and 8 AM and at 8 and 10 PM
• Iron


  Peaks early to late morning; decreases up to 30% during the day
• Calcium


  4% decrease supine (lying down)
• Exercise


  Increases creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LD)
• Exercise


  Increases potassium by 0.3 - 1.2 mmol/L for mild to moderate exercise, and 2-3 mmol/L for exhaustive exercise
• Exercise


  Decreases serum gonadotropins and sex steroids in long-distance athletes
• Exercise


  Increases prolactin in long-distance athletes, producing milk
• Diet


  Elevated ammonia, urea, and uric acid levels in patients on high-protein diets (meat, eggs, beans)
• Caffeine consumption


  Increases cortisol and ACTH levels
• Carbohydrate or sugar ingestion


  Increases blood glucose levels dramatically
• Excessive fluid intake


  Decreases hemoglobin levels due to dilution effect
• Excessive fluid intake


  Causes electrolyte imbalance
• Ingestion of foods high in fat or cholesterol


  Increases lipid levels
• Ingestion of meat, fish, iron, or horseradish


  May cause false positive results on stool occult blood tests
• Chronic alcohol consumption


  Increases TAG/TGY, liver enzymes, and liver function tests
• Stress


  Causes transient elevations in white blood cell count
• Stress


  Induces production of ACTH, cortisol, and catecholamines
• Upright posture


  Increases hydrostatic pressure, reducing plasma volume and increasing concentration of proteins (hemoconcentration)
• Upright posture


  Increases albumin and calcium levels
• Upright posture


  Causes up to 15% variation in total and HDL cholesterol
• Tourniquet application


  Increases serum enzymes, proteins, and protein-bound substances like cholesterol, calcium, and triglycerides
• Prolonged tourniquet application


  Results in venous stasis and hemoconcentration
• Newborns


  Have higher levels of fetal hemoglobin (HbF)
• Newborns


  Have bilirubin concentration that rises after birth and peaks around 5 days
• Newborns


  Have lower glucose levels than adults
• Skeletal growth and muscle development

  Increases serum alkaline phosphatase and creatinine levels
• Aging


  Decreases secretion of triiodothyronine (T3), parathyroid hormone, aldosterone, and cortisol
• Aging


  Decreases testosterone secretion in men after age 50, and increases pituitary gonadotropins in women
• Children


  Have 3-5% of adult blood volume
• Gender


  After puberty, men have higher alkaline phosphatase, aminotransferase, creatine kinase, and aldolase levels