Introduction to laboratory tests

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Introduction to laboratory tests
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Collection of specimens
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Red Top

• Red Top No additive
• Used to separate serum
• Used for chemistry panels

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Blue top

• Contains sodium citrate
• Prevents clotting when plasma needs to be tested
• Used for Hematology, PT/PTT

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Purple top

• Contains EDTA
• Prevents blood from clotting
• Used for CBC, platelet counts, heme

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Potential complications

• From the blood draw bleeding, hematoma,
  faintness, infection
• Preventing interfering factors Hemolysis,
  drawing blood from an arm with an IV running
  (why?), drawing from an arm with AV dialysis
  fistula. Avoid tourniquet for gt 1 minute.

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Favorite tests/panels to become well acquainted
with

• CBC
• Blood chemistry
• Coagulation tests
• Lipid profile
• Liver function tests (LFTs)
• Renal profile
• Thyroid panel

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The CBC

• Common, inexpensive, routine, and valuable test
• Used to evaluate anemias, response to infection,
  adequacy of platelet component of clotting system.

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Cell types
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The CBC (Complete Blood Count)

• RBC count
• Hemoglobin
• Hematocrit
• RBC indices
• WBC count and differential
• Platelet count
• Blood smear

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RBC count

• Males 4.7-6.1
• Females 4.2-5.4
• Newborns 4.8-7.1
• (In RBC X 106/uL)

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RBC indices

• MCV
• MCH
• MCHC
• RDW
• Indicators of amount and size of RBCs, which
  gives information about different types of anemia

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Peripheral smear
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Iron deficiency anemia
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Hemoglobin

• Males 14-18 g/dl
• Females 12-16 g/dl
• Newborns 14-24 g/dl (decreases to 10-17 g/dl by 6
  mos)
• Hgb below 8 (more or less) usually means
  TRANSFUSION needed

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Hematocrit
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Hematocrit

• Males 42-52
• Females 37-47 (pregnantgt33)
• Kids look up, but generally NOT under 30,
  higher in first months of life)

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WBC (White Blood Cell)

• Two parts The Total count and the Differential
• Total count generally given as 5,000-10,000/cc3
  (kids and newborns higherlook up!)
• Critical values lt2,500 or gt30,000 (why)

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The Differential
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Distribution among lab students
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• CBC
• Blood chemistry
• Coagulation tests
• Lipid profile
• Liver function tests (LFTs)
• Renal profile
• Thyroid panel

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Chemistry panel (screen, profile)

• Sodium (135-145 mEq/L)
• Potassium (3.5-5 mEq/L)
• Chloride (98-106 mEq/L)
• CO2 (23-30 mEq/L)
• Blood urea nitrogen (BUN) (10-20 mg/dL)
• Creatinine (0.5-1.5 mg/dl)

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• CBC
• Blood chemistry
• Coagulation tests
• Lipid profile
• Liver function tests (LFTs)
• Renal profile
• Thyroid panel

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Coagulation tests

• PT (prothrombin time)
• PTT or aPTT (partial thromboplastin time, or
  activated partial thromboplastin time)
• INR (International normalized ratio, a calculated
  way of getting rid of variations in laboratory
  testing of the PT)

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When you see PT or INR, think COUMADIN!
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Why you should pay attention to the INR
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When you see aPTT, think HEPARIN!
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INR

• For DVT prophylaxis 1.5-2.0
• For DVT 2.0-3.0
• For prevention of embolism in pt with atrial
  fibrillation 2.0-3.0
• Prosthetic valve prophylaxis 2.5-3.5

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INR

• Leafy greens (Spinach!) high in vit K which
  inhibits (decreases) INR

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Heparin

• By protocol, often nurse managed standing order
  to adjust drip rate based on aPTT.

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• CBC
• Blood chemistry
• Coagulation tests
• Lipid profile
• Liver function tests (LFTs)
• Renal profile
• Thyroid panel

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Lipid Profile

• Total cholesterol lt200mg/100ml (but complex, and
  have to account for the HDLs and LDLs to assess
  risk) usually 140-199 mg/dl
• HDL 30-70 mg/dl
• LDL less than 130
• VLDL
• Apolipoproteins
• Triglycerides less than 200

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Liver function tests

• Bilirubin
• Aspartate aminotransferase (AST)
• Alanine aminotransferase (ALT)
• Gamma-glutamylo transpeptidase (GGT)
• Alkaline phosphatase (ALP)

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Renal function tests

• BUN (8-25 mg/dL)
• Creatinine (0.5-1.5 mg/dL)
• Creatinine clearance

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Thyroid panel

• T3
• T4
• TSH (2-10 uU/ml)

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Other labs of interest

• Albumin (3.5 5.0 gm/dl) The main plasma
  protein. Pulls fluid into intravascular space.
• Pre-albumin (as marker of nutritional status
  Normal 15-36 mg/dl, severe nutritional deficiency
  lt10.7 mg/dl)

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Cardiac enzymes

• Creatinine Kinase (CK)
• LDH
• Troponins Used widely as marker for MI

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Troponin 2 flavors

• Troponin I (gt 1.5ng/ml suggests MI)
• Troponin T (gt0.1 to 0.2 ng/ml suggests MI)

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Elements

• Calcium (8.6-10 mg/dL)
• Magnesium (1.6-2.6 mg/dL)
• Phosphorous (2.7-4.5 mg/dL)

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Urinalysis
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Normals, and not so normals