Unit 6 ppt

• Diurnal variation


  Fluctuations in the levels of certain substances in the body over the course of a day
• Tests 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
• 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
• Effects of exercise


  • Increase in creatine kinase (CK), aspartate aminotransferase (AST), and lactate dehydrogenase (LD)
  • Increase in potassium (mild to moderate exercise - 0.3 - 1.2 mmol/L, exhaustive exercise - 2-3 mmol/L)
  • Increase in prolactin (in long-distance athletes)
  • Decrease in serum gonadotropins and sex steroid (in long-distance athletes)
• Effects of diet


  • Elevated ammonia, urea, and uric acid levels in patients on high-protein diets
  • Increase in cortisol and ACTH levels with consumption of beverages containing caffeine
  • Increase in glucose (blood sugar) levels with ingestion of carbohydrates or sugar-laden substances
  • Decrease in Hgb levels by drinking excessive amounts of water and other fluids
  • Electrolyte imbalance due to drinking excessive amounts of water and other fluids
  • Increase in lipid levels with ingestion of foods such as butter or margarine, cheese, cream, and some enteral (tube feeding) preparations
  • False positive stool occult blood test due to ingestion of meat, fish, iron, and horseradish
  • Increase in TAG/TGY, liver enzymes, liver function tests due to chronic consumption of alcohol
• Stress


  • Emotional stress can cause transient (short-lived) elevations in WBCs
  • Mental and physical stresses induce the production of adrenocorticotropic hormone (ACTH), cortisol, and catecholamines
• Posture


  • Upright position increases hydrostatic pressure, causing a reduction of plasma volume and increased concentration of proteins
  • Albumin and calcium levels may become elevated as one changes position from supine to upright
  • Change in position from lying to standing can cause up to a 15% variation in total and high-density lipoprotein (HDL) cholesterol results
• Tourniquet application


  • May increase serum enzymes, proteins, and protein-bound substances, including cholesterol, calcium, and triglycerides
  • 1 min application
  • Prolonged application results in venous stasis (hemoconcentration)
• Age-related changes

  • Newborn - much of the Hb is Hb F
  • Bilirubin concentration rises after birth and peaks at about 5 days
  • Infants have lower glucose level than adults
  • With skeletal growth and muscle development, serum alkaline phosphatase and creatinine levels also increase
  • The elderly secrete less triiodothyronine, parathyroid hormone, aldosterone, and cortisol
  • After age 50, men experience a decrease in secretion rate and concentration of testosterone and women have an increase in pituitary gonadotropins
• Gender-related differences


  • After puberty, men have higher alkaline phosphatase, aminotransferase (alanine and aspartate), creatine kinase, and aldolase levels
  • Women have lower levels of magnesium, calcium, albumin, Hb, serum iron, and ferritin
• Common in vivo interferences


  • Tobacco smoking - high blood carboxyhemoglobin levels, increased Hb, RBC Count, MCV, and WBC Count, increased levels of insulin, epinephrine, and growth hormones, decreased sperm counts and motility and increased abnormal morphology
• Common in vitro interferences

  • Hemolysis - falsely increased potassium, magnesium, iron, lactate dehydrogenase, phosphorus, ammonium, and total protein
  • Alcohol ingestion - increases plasma concentration of uric acid, triglycerides, and gamma glutamyltransferase (GGT), causes hypoglycemia
  • Dehydration - affects RBCs, enzymes, iron, calcium, sodium, and coagulation factors
  • Drug therapy - chemotherapy drugs decrease blood cells, many drugs are toxic to the liver - increased levels of liver enzymes such as ALT, AST, LD; decreased production of clotting factors
• Problem areas to avoid and troubleshoot in site selection

  • Burns, Scars, and Tattoos
  • Damaged veins (sclerosed/hardened or thrombosed/clotted veins)
  • Edema
  • Hematoma
  • Mastectomy
  • Obesity