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PREANALYSIS

Navid Omidifar MD. AP/CP

Assistant professor of pathology

SUMS

1397

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PHASES IN CLINICAL LAB

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PREANALYTIC

  • Requesting physician
  • Patient ID
  • Patient preparation
  • Specimen collection
  • Specimen handling and transport
  • Specimen preparation
  • Specimen storage

ANALYTIC

POSTANALYTIC

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Preanalytical Errors

  • It is estimated that 70-85% of clinical decisions are based upon information derived from laboratory test results
  • 32-75% of all lab errors
  • $200,000/year in re-collection costs in a 400-bed hospital
  • Estimated average costs of a preanalytical error in North American institutions were estimated at $208, with costs representing between 0.23% and 1.2% of total hospital operating costs
  • Treatment for an injury related to a traumatic needlestick: $500–$3000
  • Poor technique: nerve and arterial damage, subcutaneous hemorrhage, infection, death
  • 385,000 needlestick /year

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Requesting physician

  • Wrong laboratory test 🡺 inappropriate interpretation of results.
  • Electronically*
    • HIS or LIS
  • Manuscript
  • Lab. Brochure or guide book

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Precollection Variables

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Patient Related variables

Constant*

  • Age
  • Gender
  • Race
  • Pregnancy
  • Obesity

Physiologic factors

  • Diurnal variation
  • Exercise
  • Fasting
  • Diet
  • Stress
  • Posture
  • Smoking
  • Alcohol consumption

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Constant variables

  • Age:
      • Age related reference values
    • Composition of analytes: Hb fractions
    • Hb, WBC, Diff,
    • Infants have a lower glucose level than adults because of their low glycogen reserve
    • ALP
  • 🡹 2 mg/dL/year in total cholesterol & 2 mg/dL/year in triglycerides until midlife
  • The elderly:🡻 T3, PTH, aldosterone, and cortisol.
  • After age 50:
  • Men: 🡻 secretion rate and concentration of testosterone
  • Women:🡹 pituitary gonadotropins, especially FSH

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Constant variables

  • Gender:
    • Sex related reference values
    • High ALP, AST, ALT, CK, Aldolase, Uric acid, Hb, Hct, RBC, serum iron, and ferritin in men
    • Sex hormones
  • Race:

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Male–female differences related to the mean value of females as given in

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Constant variables

  • Obesity
    • 🡹 TG, Cholesterol, Apo B, LDH activity, cortisol, glucose, insulin
    • 🡻 Testosterone in men

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Constant variables

  • Pregnancy
    • Increase in plasma volume:🡻Hb, Hct, Bun
    • 🡹 GFR, Urine volume
    • Pregnancy associated analytes: HCG, AFP, Alkaline phosphatase, Prolactin

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Controllable variables

  • Stress:
    • 🡹ACTH, cortisol, and catecholamines.
    • 🡹Cholesterol, 🡻 HDL (15%)
    • Hyperventilation: affect acid-base balance and 🡹 WBC, serum lactate, or free fatty acids.

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Controllable variables

  • Exercise
    • Transient:
      • 🡹FFA(30%), Alanine(180%), Lactate (300%)
      • CK, AST, LDH
      • Activate coagulation, fibrinolysis, Platelets
    • Long term
      • 🡹🡹CK, AST, Aldolase, LDH
      • Chronic aerobic: 🡹 CK, AST, ALT, LDH
    • Long-distance athletes:
      • 🡻Serum gonadotropin and sex steroid
      • 🡹Prolactin

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Controllable variables�Diet

  • Fasting:
    • 🡹Bili
    • 🡻Glucose
    • Cholestrol: no effect
  • Eating;
    • Depending on fat content:🡹 Plasma potassium, TG, ALP, 5-HIAA
    • 🡹Glucose
    • Chylomicrons 🡺 Increased serum turbidity

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Change of the serum concentration of different analytes two hours after a standard meal�

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Controllable variables�DIET type

  • Stool OB:
    • Meat, fish, iron, and horseradish
    • Peroxidase
    • False-positive occult blood reaction
  • Vegetarians: 🡻LDL, VLDL, TG, Cholesterol, vit B12
  • Protein rich: 🡹Urea, ammonia, urate
  • High unsaturated/saturated fat: 🡻cholesterol
  • Banana, pineapple, tomato, avocado: high serotonin, 🡹 5-HIAA
  • Caffeine: 🡹free fatty acids, cause catecholamine release

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Controllable variables

  • Posture
    • Standing:🡹 proteins, Ca
    • Albumin, total protein, enzymes, calcium, bilirubin, cholesterol, triglycerides, and drugs bound to proteins
    • After bed rest in the hospital: 🡻Hb; IV fluid
    • Aldostrone, plasma renin activity

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Increase (%) of plasma concentration of various analytes when changing from supine to an upright position �

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Controllable variables

  • Smoking:
    • 🡹Cerboxy Hb, catecholeamines, cortisol
      • 🡻 Eosinophils
      • 🡹Neutrophils, monocytes, and plasma fatty free acids increase
    • Chronic:🡹Hb, RBC, MCV, WBC
    • 🡹 lactate, insulin, epinephrine, and growth hormone and urinary secretion of 5-HIAA
    • 🡻B12
    • Immunoglobulins (🡻IgA, IgG, IgM 🡹IgE)
    • 🡻Sperm count and motility

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Controllable variables

  • Alcohol consumption
  • 🡹lactate, urate, and TG
  • Chronic alcohol abuse: 🡹 HDL, GGT, urate, MCV

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Diurnal variation

    • Iron
    • Prolactin
    • Cortisol, ACTH
    • WBC
    • Insulin
    • Aldosterone, plasma renin activity
    • GH
    • Urinary electrolyte

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Patients should be advised to:

Avoid changes in their diet, consumption of alcohol, strenuous exercise & smoking 24 hours before sampling

Fasting for 10-12 hrs (less than 14 hrs) for most gradients

Collect blood & urine in

early morning, 7-9 am

(with exceptions or physicians request)

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Sampling

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Patient ID

  • Identification
    • At least three patient ID data
    • patient’s name, sex, age, date of birth (DOB), date of admission, date on which measurement or examination was ordered, hospital number, room number, physician, and physician’s pharmacy code number
    • Hospital No
  • Labeling
    • Barcode
  • Photo: Drug of abuse, alcohol, medicolegal cases

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SPECIMEN COLLECTION�INDUCED INTERFERENCES

  • Hemolysis
  • Hemoconcentration
  • Failure to anticoagulate
  • Icteric serum
  • Lipemic serum (late scence)

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Interferences

  • Hemolysis
  • Problem finding a vein for phlebotomy
  • Needle that is too small
  • Pulling a syringe plunger back too fast
  • Expelling the blood vigorously into a tube
  • Shaking or mixing the tubes vigorously
  • Performing blood collection before the alcohol has dried at the collection site.
  • K , Mg, Fe, LD,AST,ALT, phosphorus, ammonium, and total protein (table)

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Interferences�

  • Hyperbilirubinemia(>25 mg/dL):
    • Albumin (HABA procedure)
    • Cholesterol ferric chloride reagents)
    • Total protein (Biuret procedure)
    • Creatinine (Jaffe reaction)

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Interferences

  • Lipemia: triglyceride>400 mg/dL
  • Inhibition of assays for amylase, urate, urea, CK, bilirubin, and total protein

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SPECIMEN COLLECTION

  • Tubes
    • May contains anticoagulants, preservatives or activator
    • Standard stopper color

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Remember :

    • Proper tube
    • Mixing
    • Correct specimen volume

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Tourniquet Effect

  • Maximum 1 min
  • The composition of blood drawn first-that is ,the blood closes to the tourniquet-is most representative of the composition of circulating blood 🡪calcium that are pertinent to critical medical decisions.
  • Blood drawn later shows a greater effect from venous stasis

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Tourniquet Effect

  • Lactate: no tourniquet
  • Prolonged tourniquet:
    • hemoconcentration 🡪 🡹serum enzymes, proteins, and protein-bound substances (cholesterol, calcium, and triglycerides)
    • Increase risk of hemolysis

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Tourniquet Effect

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Pumping of the fist

  • Fist exercise: mild hemolysis

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  • Pumping of the fist before venipuncture should be avoided 🡪 causes an increase in the plasma K, Phosphate and Lactate

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Order of Draw: Evacuated Tube and Syringe

  1. Blood-culture tubes (yellow)
  2. Coagulation sodium citrate tube (blue stopper)
  3. Serum tubes with or without clot activator or gel separator
  4. Heparin tubes with or without gel (green stopper)
  5. EDTA tubes (lavender stopper)
  6. Glycolytic inhibitor tubes (gray stopper)

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Blood storage and preservation

  • Adsorption to glass or plastic
  • Protein denaturation
  • Evaporation of volatile constituents
  • Water movement into the cells and hemoconcentration
  • Metabolic activity of cells (WBC, RBC)

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Blood storage and preservation

  • Plasma or serum should be separated from cells as soon as possible and certainly within 2 hours

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Storage

  • Prolonged contact with RBCs
    • Glucose
    • Lactate
    • Chloride and CO2
    • Potassium after 24 hrs
  • Unseparated serum and plasma:
    • Total bilirubin, sodium, urea, nitrogen, albumin, calcium, magnesium, and total protein
    • Movement of water into cells after 24 hours 🡺 hemoconcentration

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