physiolo

• This part of the module will address

  • Physiological variables
  • Problem venipuncture sites
  • Various types of vascular access devices
  • Patient complications and conditions
  • Procedural errors
  • Specimen quality issues
• Reference range


  Values which patient results are compared to. Mostly doctors will also look for previous results of the same patient, if applicable
• Basal state


  The resting metabolic state of the body early in the morning after fasting for approximately 12 hours. A basal state specimen is ideal for establishing reference ranges on inpatients because the effects of diet, exercise, and other controllable factors on test results are minimized or eliminated
• Basal state is influenced by a number of physiologic patient variables: age, gender, conditions of the body that cannot be eliminated
• Outpatient specimens


  • Are not basal-state specimens and may have slightly different reference ranges or normal values
• Age


  Values for blood components vary considerably depending upon the age of the patient
• Examples of age-related changes

  • RBC and WBC values – normally higher among newborns than in adults
  • Kidney functions decrease with age (example of test: creatinine clearance)
• Altitude


  Test results for some blood analytes show significant variation at higher elevations compared with results at sea level
• Analytes affected by high altitude

  • Increased levels: RBC count, Hemoglobin, Hematocrit, Uric acid
  • Decreased levels: Urinary creatinine, Plasma renin
• Analytes generally take weeks to adapt to high elevations/altitude; however, they adapt to return to sea level within days
• Dehydration


  The decrease in body fluid. Dehydration may happen with persistent vomiting or diarrhea, which causes hemoconcentration, a condition in which blood components that cannot easily leave the bloodstream become concentrated in the smaller plasma volume
• Analytes that increase during dehydration

  • RBC, Enzyme, Iron, Calcium, Sodium, Coagulation factors (clotting factors)
• Dehydrated patients may not accurately reflect the patient's normal status. It is often difficult to obtain blood specimens from dehydrated patients
• Fasting


  Strictly no ingestion of food approximately 8-12 hours overnight. Though drinking of water is allowed for some fasting patients, patients who were advised not to drink water (NPO: "nil per os", meaning nothing by mouth) for another procedure should be strictly followed
• Overfasting: fasting beyond 12 hours can cause serious health problems, such as electrolyte imbalance and heart rhythm disturbances, therefore patients who fasted beyond 12 hours will not be accepted for testing that requires fasting
• Examples of how some analytes can be significantly affected by the consumption of certain types of food or drink and the excess consumption of some fluids

  • Ammonia, urea, and uric acid levels may be elevated in patients on high-protein diets
  • Cortisol and Adrenocorticotropic hormone (ACTH) levels have been shown to increase with the consumption of beverages containing caffeine
  • Glucose (blood sugar) levels increase dramatically with the ingestion of carbohydrates or sugar-laden substances but return to normal within 2 hours if the patient has normal glucose metabolism
  • Hemoglobin levels can decrease and electrolyte balance can be altered by drinking excessive amounts of water and other fluids (dilutional effect)
  • Lipid levels increase with ingestion of foods such as butter or margarine, cheese, cream, and some enteral (tube feeding) preparations
  • Triglycerides, certain liver enzymes, and other liver function analytes are increased by chronic consumption or recent ingestion of large amounts of alcohol, which can also cause hypoglycemia (low blood sugar)
• Effects of long-term starvation

  • Increased levels: Creatinine, Ketone, Uric acid,
  • Decreased levels: Cholesterol, Triglycerides, Urea
• Diurnal/Circadian variations


  The levels of many blood components normally exhibit diurnal (happening daily) or circadian (having a 24-hr cycle) variations or fluctuations
• Factors that play a role in diurnal variations

  • Posture
  • Activity
  • Eating
  • Being awake or asleep
  • Daylight and darkness
• Examples of analytes with diurnal/circadian variations

  • Melatonin – increase at night and decrease during daylight hours
  • Cortisol – peaks around 8 am
  • Renin and Thyroid-stimulating hormone – peaks at pre-dawn hours of the morning during sleep
  • Aldosterone, Bilirubin, Cortisol, Hemoglobin, Insulin, Iron, Potassium, Testosterone, RBC – peaks in the morning
  • Eosinophils, Creatinine, Glucose, Growth hormone, Triglycerides, and Phosphates – normally lowest in the morning
• Drug therapy


  Some drugs alter physiological functions, causing changes in the concentration of certain blood analytes. Drugs can also interfere with the actual test procedure, causing false increases or decreases in test results
• Exercise


  Exercise affects a number of blood components, raising levels of some and lowering levels of others. Effects vary, depending on the patient's physical condition and the duration and intensity of the activity
• False-negative result


  A drug may compete with the test reagents for the substance being tested, causing a falsely low result
• False-positive result


  The drug may enhance reaction, causing a falsely high result
• Drugs that can alter physiologic function and the analytes they affect

  • Chemotherapy drugs - increased WBC, platelets
  • Most drugs (that are toxic to liver) - increased AST, ALP, LDH, decreased clotting factors
  • Oral contraceptives - decreased erythrocyte sedimentation rate (ESR), decreased Vitamin B12
  • Steroids and diuretics - increased amylase, lipase
  • Thiazide diuretics - increased calcium, glucose, decreased sodium & potassium
• Drugs that interfere with BLOOD TESTS should be stopped or avoided 4 to 24 hours prior to obtaining blood samples for testing
• Drugs that interfere with the URINE TESTS should be avoided for 48 to 72 hours prior to the urine sample collection
• Effects of exercise on blood components

  • Increased - glucose, creatinine, insulin, lactic acid, total protein, potassium
  • Decreased - arterial pH, carbon dioxide, platelets
• Creatine kinase (CK) & Lactate dehydrogenase (LDH) remain elevated for 24 hours or more after exercise
• Cholesterol can remain elevated for up to 1 hour after exercise has stopped
• Fever


  Affects the levels of a number of hormones, increases insulin, glucagon, cortisol
• Gender


  • RBC, hemoglobin and hematocrit values are higher among males than females
• Intramuscular injection


  Can increase levels of creatine kinase (CK) and the skeletal muscle fraction of LDH
• CK and LDH levels should be drawn before intramuscular injection or at least 1 hour after injection
• Jaundice


  • Characterized by increased bilirubin in the blood, leading to yellow appearance
  • Can interfere with blood chemistry tests based on color reactions and reagent-strip analyses on urine
• Body position


  • From supine to upright position causes blood fluids to filter into tissues, decreasing plasma volume and increasing concentration of protein-bound components
  • Standing position increases RBC count and potassium ion levels
• Lipid profiles should be collected after the patient has been either lying down or sitting quietly for a minimum of 5 minutes
• Pregnancy

  Increases body fluids, leading to lower RBC count
• Effects of smoking


  • Increased - cholesterol, growth hormone, cortisol, triglycerides, glucose, WBC count
  • Increased - RBC count, hemoglobin levels
  • Decreased - immunoglobulins IgA, IgG, IgM
  • Increased - immunoglobulin IgE
• Skin-puncture specimens may be difficult to obtain from smokers because of impaired circulation in the fingertips