Laboratory Analysis

Overview of Basic Blood Hematology and Coagulation Tests

• Composition of Blood:   - Total volume: 5 L of blood, which is approximately 1/13 of body weight.   - Contains:     - 3 L plasma     - 2 L cells

• Plasma:   - Derives from intestines and lymphatic system.   - Functions as a vehicle for cell movement.

• Cells:   - Produced by bone marrow.   - Classified into:     - White cells (leukocytes)     - Red cells (erythrocytes)     - Platelets (thrombocytes)

Blood Tests

• Basic tests address disorders of hemoglobin (Hb), cell production (hematopoiesis), synthesis, and function.

• Specimen Collection Techniques:   - Capillary Skin Puncture:     - Preferred for a peripheral blood smear.     - Adults: Skin puncture through fingertips.     - Children: Skin puncture through fingertips.     - Infants: Skin puncture on the great toe or side of the heel.   - Venipuncture:     - Allows procurement of large quantities of blood for testing.     - Preferred site: Ante cubital veins.     - Blood values remain constant across different venipuncture sites.   - Bone Marrow Aspiration:     - Used to collect bone marrow specimens for various hematologic disorders and infectious diseases.

Procedural Alerts for Blood Collection

• Capillary Puncture:   - Do not squeeze the site to obtain blood – this may alter blood composition and invalidate test values.   - Warming the extremity or having it in a dependent position may facilitate specimen collection.

• Venipuncture:   - Never draw blood from the same extremity used for IV medications, fluids, or transfusions. If unavoidable, ensure the venipuncture site is below the IV site.   - If there are two failed attempts, a physician or highly trained phlebotomist should be called for assistance.

• Arterial Puncture:   - Necessary for arterial blood gas (ABG) determinations or when venous samples cannot be obtained.   - Blood can be collected from:     - Radial artery     - Brachial artery     - Femoral artery.   - The sample must be placed in an ice slurry and transported to the laboratory to prevent metabolic alterations post-draw.

Arterial Blood Gas (ABG) Testing

• Used to assess oxygenation, ventilation, and evaluate acid-base status by measuring:   - PCO2, PO2, pH, O2CT, SaO2, HCO3.

Bone Marrow Aspirations

• Important for evaluating hematologic disorders and infectious diseases such as leukemia, multiple myeloma, lymphoma, anemia, and pancytopenia.

• Can be collected via aspiration or biopsy.

Complete Blood Count (CBC)

• A basic screening test and one of the most frequently ordered laboratory procedures.

• Provides Valuable Information About:   - Hematologic and other body systems.   - Prognosis and response to treatment.   - Recovery status.

• Components of CBC:
    - WBC (White Blood Cell Count):     - Functions to fight infection.   - Differential WBC Count:     - Indicates specific patterns and types of WBCs present.   - RBC (Red Blood Cell Count):     - Function to carry oxygen from lungs to tissues and carbon dioxide from tissues to lungs.   - Hematocrit (Hct):     - Measures RBC mass.   - Hemoglobin (Hb):     - Main component of RBCs; transports O2 and CO2.   - Mean Corpuscular Volume (MCV):     - Indicator of average size of RBCs.   - Mean Corpuscular Hemoglobin (MCH):     - Measures the average amount of hemoglobin per RBC.   - Mean Corpuscular Hemoglobin Concentration (MCHC):     - Concentration of hemoglobin in RBCs.   - Platelet Count:     - Necessary for clotting and control of bleeding.   - Mean Platelet Volume (MPV):     - Indicates platelet production index.   - Red Blood Cell Distribution Width (RDW):     - Indicates degree of variability and abnormal cell size.

Normal Values for Complete Blood Count (>18 years)

Clinical Implications of Blood Work

• WBC:   - Leukocytosis:     - Definition: WBC > 11,000/mm³ or > 11.0 x 10³/mm³.     - Common occurrence in acute infections.   - Leukopenia:     - Definition: WBC < 4000/mm³ or < 4.0 x 10³/mm³.     - Common in viral infections and some bacterial infections.     - Critical Value: WBC < 500/mm³ (dangerous, often fatal).

• RBC, Hct, Hb:   - Decreased Values:     - Indicative of anemia, Hodgkin’s disease, multiple myeloma, leukemia, or acute/chronic hemorrhage.   - Increased Values:     - Linked to polycythemia vera, renal disease, pulmonary disease, or cardiovascular disease.   - Critical Values:
      - Hct < 20% (risk of cardiac failure and death).     - Hct > 60% (risk of spontaneous clotting).     - Hb < 5.0 g/dL (risk of heart failure and death).     - Hb > 20.0 g/dL (risk of hemoconcentration and clogging of capillaries).

Coagulation Mechanism

• Protects the integrity of blood vessels while maintaining the fluid state of blood.

• Typically performed for patients with bleeding disorders, vascular injury or trauma, or coagulopathies.

Common Coagulation Tests

• Prothrombin Time (PT):

• Partial Thromboplastin Time (PTT):

• Activated Partial Thromboplastin Time (APTT):

• Bleeding Time:

• Thrombin Time (TT):

Clinical Implications for Platelets

• Normal Values:   - Adult: 140 – 400 x 10³/mm³ or 140 – 400 x 10⁹/L   - Children: 150 – 450 x 10³/mm³ or 150 – 450 x 10⁹/L

• Critical Value:
    - Platelets < 20 x 10³/mm³ indicates spontaneous bleeding and prolonged bleeding time.

• Thrombocytosis:   - Definition: Abnormally increased platelets.   - Causes: Leukemia, myeloproliferative diseases, iron-deficiency anemia, rheumatoid arthritis, acute infections, chronic pancreatitis.

• Thrombocytopenia:   - Definition: Abnormally decreased platelets.   - Causes: Idiopathic thrombocytopenic purpura, viral/bacterial infections, HIV, alcohol toxicity.

Clinical Implications of PTT/APTT

• PTT and APTT:   - Both test similar functions, with APTT being a more sensitive version used to monitor heparin therapy.

• Normal Value:   - APTT: 21.0 – 35.0 seconds

• Critical Value:   - APTT > 70 seconds indicates potential for spontaneous bleeding.

Clinical Implications for PT

• Prothrombin production relies on adequate vitamin K intake and absorption.

• Normal Value:   - PT: 11.0 – 13.0 seconds (may vary by laboratory)

• International Normalized Ratio (INR):   - A comparative rating of PT ratios adjusted by the International Reference Thromboplastin.

• Critical Values:   - If PT > 30 seconds, vitamin K may be administered.   - PT > 20 seconds (for non-anticoagulated persons) warrants concern.   - Critical value of INR > 3.6 necessitates clinician notification.

Chemistry Studies

• Purpose: Identifies various chemical blood constituents across several test categories:   - Enzymes   - Electrolytes   - Blood sugars   - Lipids   - Hormones   - Proteins   - Vitamins   - Minerals   - Drug investigations.

Common Screening Profiles

Renal Panel

• BUN (Blood Urea Nitrogen):   - Used as an index of glomerular function in the production and excretion of urea.   - Normal Range:
      - Adults: 6 – 20 mg/dL or 2.1 – 7.1 mmol/L   - Critical Value:
      - >100 mg/dL (>35 mmol/L).   - Increased BUN Levels:     - Impaired renal function, chronic renal disease, urinary tract obstruction.   - Decreased BUN Levels:     - Liver failure, malnutrition, low-protein diet, impaired absorption.

• Albumin:   - Evaluates nutritional status, albumin loss in acute illness, liver disease, and renal disease.   - Normal Range (Adults):     - 3.5 – 5.2 g/dL or 35 – 52 g/L.   - Critical Value:     - <1.5 g/dL or 15 g/L.   - Increased Albumin:     - Associated with dehydration.   - Decreased Albumin:     - Due to acute and chronic inflammation, infections, liver disease, alcoholism, or renal disease.

• Creatinine:   - Used to diagnose impaired renal function.   - Critical Values:     - Men: 0.9 – 1.3 mg/dL or 80 – 115 µmol/L;     - Women: 0.6 – 1.1 mg/dL or 53 – 97 µmol/L.   - Increased Creatinine Levels:     - Indicative of impaired renal function, chronic nephritis, urinary tract obstruction.   - Decreased Creatinine Levels:     - Associated with small stature, decreased muscle mass, or liver disease.

Clinical Implications of Enzyme Studies

• Creatine Kinase (CK):   - An enzyme indicating higher concentrations in heart and skeletal muscles.   - Normal Range:     - Men: 38 – 174 U/L (0.63 – 2.90 µkat/L);     - Women: 26 – 140 U/L (0.46 – 2.38 µkat/L).   - Increased CK:     - Indicative of acute myocardial infarction (MI).   - Decreased CK:     - Lacking diagnostic meaning; may indicate low muscle mass or bed rest.

Clinical Implications of Liver Function Tests

• Bilirubin:   - Byproduct of hemoglobin breakdown in RBCs; results from hemolysis.   - Two forms:     - Indirect (unconjugated) bilirubin     - Direct (conjugated) bilirubin.   - Normal Ranges (Adult):     - Total: 0.3 – 1.0 mg/dL or 5 – 17 µmol/L;     - Conjugated (direct): 0.0 – 0.2 mg/dL or 0.0 – 3.4 µmol/L.   - Elevated Total Bilirubin Levels:     - Accompanied by jaundice due to hepatic, obstructive, or hemolytic causes.   - Elevated Indirect Bilirubin Levels occur in:     - Hemolytic anemia due to a large hematoma or trauma associated with a large hematoma.   - Elevated Direct Bilirubin Levels occur in:     - Cancer of the head of the pancreas and choledocholithiasis.

• Alkaline Phosphate (ALP):   - Used as an index of liver and bone disease.   - Normal Ranges (Adult):     - 25 – 100 U/L or 0.43 – 1.70 mkat/L.   - Elevated ALP occurs in:     - Obstructive jaundice and liver cirrhosis.   - Decreased ALP:     - Associated with malnutrition and hypothyroidism.

Clinical Implications of Electrolyte Tests

• Electrolytes:   - Critical for cellular reactions, supporting a variety of cellular functions including nerve impulse transmission, muscular contraction, and water balance.

• Calcium (Ca²⁺):   - Stored in the skeleton and teeth; 50% ionized, the remainder is protein-bound.   - Normal Ranges (Adults):     - Total calcium: 8.8 – 10.4 mg/dL or 2.20 – 2.60 mmol/L     - Ionized calcium: 4.65 – 5.28 mg/dL or 1.16 – 1.32 mmol/L.   - Hypercalcemia (increased levels):     - Associated with hyperparathyroidism and cancer.   - Hypocalcemia (decreased levels):     - Linked to decreased albumin, hypoparathyroidism, and malabsorption.

• Chloride (Cl⁻):   - Maintains cellular integrity.   - Normal Ranges (Adults):     - 96 – 106 mEq/L (96 – 106 mmol/L).   - Decreased Cl⁻ Levels:     - Caused by severe vomiting, gastric suction, chronic respiratory acidosis, metabolic alkalosis.   - Increased Cl⁻ Levels:     - Seen in dehydration, Cushing’s syndrome, hyperventilation (respiratory alkalosis), and metabolic acidosis.

• Potassium (K⁺):   - Principal electrolyte of intracellular fluid, important for nerve conduction and muscle function.   - Normal Range (Adult):     - 3.5 – 5.2 mEq/L or 3.5 – 5.2 mmol/L.   - Decreased K⁺ Levels (hypokalemia):     - Can occur from diarrhea, vomiting, sweating, starvation, malabsorption.   - Increased K⁺ Levels (hyperkalemia):     - Result of renal failure, dehydration, obstruction, trauma, and metabolic acidosis.

• Sodium (Na⁺):   - Most abundant cation (90% of electrolyte fluid) acting as the chief base of blood.   - Primary function is maintaining osmotic pressure and acid-base balance, transmitting nerve impulses.   - Normal Range (Adult):     - 136 – 145 mEq/L (136 – 145 mmol/L).   - Hyponatremia (decreased levels):     - Reflects relative excess of body water rather than low total-body sodium.     - Caused by excessive fluid loss, nephritis, and diuretics.   - Hypernatremia (increased levels):     - Uncommon but can occur in dehydration and insufficient water intake, sometimes in coma.

Tumor Markers

• Definition:   - Proteins produced by the body in response to cancer growth or by the cancer tissue itself, detectable in blood, urine, or tissue samples.

Common Tumor Markers

• AFP (Alpha-feto protein):   - Associated with liver and germ cell cancer of ovaries/testes.   - Normal levels: usually < 10 ng/mL.

• CA 15-3 (Cancer antigen 15-3):   - Linked to breast cancer; also signifies other cancers.   - Normal level: usually < 30 U/mL.

• CA 19-9 (Cancer antigen 19-9):   - Associated with pancreatic, colorectal, and bile duct cancers.   - Normal blood levels: < 37 U/mL.

• CEA (Carcino-embryonic antigen):   - Associated with colorectal, lung, breast, thyroid, pancreatic, liver, cervix, and bladder cancers.   - Levels > 3 ng/mL are abnormal.

• PSA (Prostate-specific antigen):   - Used for prostate cancer screening and diagnosis.   - PSA < 4 ng/mL: unlikely cancer; > 10 ng/mL: likely cancer.

Conclusion

• The knowledge of blood specimen collection techniques and laboratory analysis is vital for effective patient care and the assessment of health status in various clinical scenarios.