CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Objectives
1. Interpret routinely used laboratory tests e.g., CBC, basic metabolic panels and liver function tests
2. Establish differential diagnoses based on laboratory tests
3. Use laboratory tests to screen for diseases as well as monitor course and prognosis
4. Use laboratory tests in the clinical management of patients.
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Introductory Information
1. Guidelines to the Interpretation of Laboratory Data
· Limits of “normal” are determined by calculating the mean and standard deviation of values taken from a presumably “healthy” population.
· Specificity, Sensitivity, and Predictive Values
- Screening Tests
1. A screening test is useful if detection of a disease can prevent its complications.
2. Screening tests are useful for diseases that are frequently encountered in the study population.
3. The test should be:
· Highly sensitive
· Inexpensive
· Easy to perform
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Physiological Factors Affecting Laboratory Values
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. Posture
· Change in blood volume
· Change in concentration of serum constituents
↑ K+
↑ Albumin
2. Exercise
· Hypoglycemia
· ↑ lactate
· ↑ renin à ↑ BP
3. Circadian Variation
· Hormones
· Renin (highest early morning during sleep)
· Travel leads to change
4. Blindness
· Stimulation of hypothalmic pituitary axis is reduced
· Reduction in 17-hydrox ycorticosteroids and 17-ketosteroids
5. Specific Foods and Beverages
· Caffeine
↑ Catecholamine
↓ Cholesterol
↑ Triglycerides
↑ Serum gastrin
· Bran – inhibits absorption of certain constituents
Calcium
Cholesterol
Triglycerides
· Bananas
↑ Serotonin
· Avocados
Affect insulin secretion
· Onions
Reduces insulin response to glucose
6. Fasting
· Cholesterol
· Glucose
7. Smoking
· Stimulation of adrenal medulla
↑ Epinephrine
· Delayed response to insulin
· ↑ Hemoglobin
Secondary polycythemia
· Hyperlipidemia
· ↓ Immunoglobins
8. Alcohol
· gGT ↑
· ↑ Triglyceride formation in the liver
· ↓ Removal of chylomicron
9. Drugs
· Diuretics
Hypokalemia (thiazides)
· Phenytoin
↓ Serum calcium
↓ Bilirubin (due to ↑ synthesis of bilirubin conjugating enzymes)
Induction of SLE (+ ANA) thiazides
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Underlying Medical Conditions
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. Fever
· ↑ Insulin
· ↑ Cortisol
· Accelerates lipid metabolism
2. Shock and Trauma
· Hemoconcentration
3. Influence of Age, Gender & Race
4. Age
· Newborn
High Hb
High lymphocytes
High bilirubin
Low glucose (low glycogen reserves)
· Elderly
↓ Creatinine clearance
↓ Hormones
5. Gender - Men
Higher Hb
Lower g globulins
Higher cholesterol
6. Race
· CPK > In Blacks
· Albumin > in Whites
· CPK > in Blacks
· Lipids < Asians
7. Environmental Factors
· Altitude
↑ Hb
· Hard water areas
↑ Cholesterol
↑ Triglycerides
8. Diet
· High protein diet
↑ BUN
· Low-fat diet
↓ Cholesterol
· Vegetarians
↓ Lipids
· Malnutrition
Vitamin deficiencies
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Vignette
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. A previously healthy 13-year-old boy presents with jaundice for 3 months.
2. Tests:
· Bilirubin 11, Indirect 7
· AST 500, ALT 450
3. Differential diagnosis
·
4. Additional tests
·
5. Final diagnosis
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
· Alk phos 400
- Bilirubin Metabolism
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. Production
· Bilirubin: end product of heme metabolism
· Heme degraded to biliverdin by heme oxygenase
· Biliverdin converted to bilirubin by biliverdin reductase
2. Unconjugated bilirubin
· binds to albumin
· water soluble
· delivered to the liver
3. Uptake
· Binding to anion binding protein
Rifampin can impair this step
4. Conjugation
Bilirubin is glucuronidated or conjugated
o A must for the release of bilirubin in the bile
· The enzyme is UDP glucuronosyltransferase
(uridine diphosphoglucuronate-glucuronosyltransferase)
Or UGT à endoplasmic reticulum.
UGT1A1
5. Secretion
· Conjugated bilirubin secreted in bile
· Impairment of secretion
Dubin-Johnson Syndrome
Rotor Syndrome
ð Conjugated hyperbilirubinemia
6. Excretion
· Conjugated bilirubin is excreted into the small intestine via the biliary tract to the Ampulla of Vater
· Intestine
Stercobilirubin à stools
Urobilinogen à kidney à urine
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Types of Jaundice
1. Unconjugated hyperbilirubinemia: > 80% unconjugated bilirubin
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
· Prehepatic Hemolysis
Low Hb
Low Haptoglobin
↑ LDH1
AST and ALT normal
High retic counts
Abnormal RBCs morphology
Urine urobilinogen ↑
· Hepatic
Neonatal
o Immature conjugating enzymes
o Reversible
· Gilbert syndrome
Autosomal dominant
Mutations in the UGT promoter
↓ Bilirubin UDP glucoronyl transferase
Impaired conjugation
Clinical Presentation
o Asymptomatic
o Mild ↑ in indirect bilirubin < 5 mg/dl
o Normal liver function
· Crigler-Naijar Syndrome
Rare autosomal recessive
Mutations in coding region of UGT
Gene fails to make a working enzyme (bilirubin glucoronyltransferase)
Type I
o Rare
o Fatal in infants (kernicteus)
o Absent UGT
o Normal histology
Type II (Arias syndrome)
o Benign
o Diagnosed by age 1
o ↓ in UGT
o Normal histology
o Can be managed by barbiturates
§ Stimulates the production of UGT
· Assessment of Unconjugated Hyperbilirubinemia
Assess for hemolysis
o Reticulocyte count
o Peripheral smear
o Haptoglobin
o LDH1
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Conjugated Hyperbilirubinemia
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
· Intrahepatic cholestasis
Direct bilirubin < 5
Alkaline phosphatase < 500
1. Drugs
o Steroids
o Phenothiazine
2. Primary biliary cirrhosis
o Puritus
o Middle aged female
o Positive anti-mitochondrial antibody
o Granulomas
o Low CD4
3. Sclerosing cholangitis
o Males
o Severe pain
o Onion skinning of small bile ducts
· Extrahepatic Obstruction
Direct bilirubin > 5
Alkaline phosphatase > 500
Stones
Tumors
Strictures
· Lab Findings in Conjugated Hyperbilirubinemia
↑ Urine bilirubin
Elevated alkaline phosphatase
Moderate elevation of ALT and AST
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
o Elevated GGT
- Hereditary Jaudince
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. Rotor Syndrome
· Defective hepatic uptake and storage of organic anions
· Normal LFT
· Normal histology
· Benign course
· Autosomal recessive
2. Dubin-Johnson Syndrome
· Autosomal recessive
· Impaired transport of organic anions
· Intermittent jaundice
· Benign course
· Yellow black pigment in hepatocytes
· Normal LFTs
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
3. Clinical Presentation
· Intermittent jaundice
· Benign course
4. Histology
· Yellow-black pigment in hepatocytes
5. Tests
· ↑ Urine coproporphyrins
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Mixed Hyperbilirubinemia :Hepatocellular Diseases
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. Alcoholic liver disease
2. Cirrhosis, any type
3. Hepatitis
4. Drugs isoniazid
5. Labs
· Elevated AST and ALT
· Normal or slight ↑ in alkaline phosphatase
· Normal or slight ↑ in GGT
· Urine bilirubin ↑
· Urobilinogen ↓
6. Both unconjugated and bilirubin conjugated ↑↑
7. In alcoholic liver disease
· AST/ALT 2:1
8. In viral hepatitis
· AST/ALT 0.5-0.8
- Transaminases
1. ALT (alanine aminotransferase) specific
2. AST (aspartate aminotransferase(non- specific)
· Liver
· Heart
· Kidney
· Brain
- Alkaline Phosphatase
1. Sources
· Liver
· Placenta
· Bones
· Intestines
2. Clinical value
· Used in diagnosing liver and bone diseases
Liver heat stable
Bone heat labile
· Cell surface enzyme of bile ducts
· Obstruction of synthesis à release from cells
3. Causes of ↑ in alkaline phosphatase
1. Cholestasis
↑ Bilirubin
↑ GGT
↑ 5¢ NT
2. Bone disease
Pagets
o ↑ Alkaline phosphatase
o Normal bilirubin
o Normal GGT
o Normal 5¢ NT
3. Others
Pregnancy
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Other Liver Enzymes
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
1. GGT - 5¢ NT – LAP
· Gamma glutamictranspeptidase (GGT)
· 5¢ Nucleotidase (5¢ NT)
· Leucine aminopeptidase (LAP)
· Cell surface enzyme specific to biliary ducts
· GGT ↑ in alcoholic liver diseases
Present in SER
Alcohol causes microsomal proliferation and ↑ GGT
2. Ammonia
· Colon à Portal Circulation à Liver à detoxicied à Urea
· If no detoxification, serum ammonia ↑
· Liver diseases
Cirrhosis
Reyes syndrome
Nash
Drug toxicity
Amiodorone
· Impaired liver function and:
high protein in diet
Uremia
↑ Protein catabolism (fever – malnutrition)
· Measurement
NADPH conversion to NAD
Sample should be on ice
Ammonia ↑ at room temp
· Interferences
Hemolysis ↑ ammonia levels
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- BLOOD: Hb 8
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
o Anemia Classification
· MCV < 80 microcytic
· MCV 80-100 normocytic
· MCV > 100 macrocytic
1. Microcytic Hypochromic
· Iron Deficiency Anemia
Fe → Fe ↓ TIBC ↑
Reticulocytes ↓
Serum Ferritin ↓
Bone marrow: absent iron
· Thalassemia Minor: Normal Serum Ferritin
Thalassemia → Hb Electrophoresis
HbF Major
HbA2 Minor
HbA2++ F Minor
Peripheral Smear
o Microcytic hypochromic cells
· Thalassemia Major
Peripheral Smear
o Polychromasia
o Nucleated RBC’s
o Target Cells
2. Microcytic Hyperchromic
· Congential Spherocytosis
· ↑↑ Osmotic Fragility
3. Macrocytic High MCV >100
· Pernicious Anemia, ↓B12
↓Intrinsic Factor
Antiparietal antibodies +
Macrocytes, hypersegmented PMN’s
Anti intrinsic antibodies ++
↑ LDH1 (intramedullary hemolysis)
Achlorhydria (atrophic gastritis)
Schilling test (historic value)
o Oral radioactive B12 + B12 IM
o Check urine radioactivity
§ If radioactive B12 in urine = normal
§ If no radioactive B12 in urine (?PA)
§ Repeat test with oral intrinsic factor
§ If radioactive B12 in urine = PA
§ If no radioactive B12 in urine after adding intrinsic factor, proceed to step 3. Treat with tetracycline for weeks, then repeat test again.
· Folate deficiency, Folate ↓↓
· Hypothyroidsim
· Liver Diseases
Low Folate
Target Cells
↑↑ Liver Enzymes
↑ Bilirubin
· Drugs
Cytotoxic drugs
Antifolate
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
4. Normocytic
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
· Hemolytic
High reticulocytes
High total LDH and LDH1
Decreased haptoglobin
Increased total and indirect bilirubin
Enzymes Deficiency
o G6PD ↓ ↓ → Heinzbodies
o Bite cells on peripheral blood smears
Hemoglobinopathies
o S → sickle cells HB electrophoresis
o C → target cells and splenomegaly HB electrophoresis
Others
o Antibodies (autoimmune)
o Coomb’s test positive
o Peripheral smear microspherocytes
o Warm igG à Autoimmune disease
o Cold IgM à Infections mono or Mycoplasma
Membrane Defects
o PNH (paroxysmal nocturnal hemoglobinuria
o HAM Test (old test)
o Complement Sensitivity
o Slightly acidotic at night
o Flow cytometry CD55 negative
o CD59 negative
· Mechanical (Microangiopathic)
DiC → Fibrin split products prolonged APTT
Scleroderma → SCL 70+
HUS → E. coli 0157
TTP
o low grade fever
o thrombocytopenia
o transient neurologic deficits
o renal failure
o anemia
o schistocytes
· Aplastic à Bone marrow failure
Diagnose bone marrow
o Dry tap
o Bx accellular
If pure red cell aplasia, check for thymoma
· Bone Marrow Replacement (Myelophthisic)
Leukemia
Fibrosis
Granulomas
Metastatic disease
· Acute blood loss
· Chronic disease
Renal failure à Low erythropoietin
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Blood lab values
1. Reticulocyte count
· Low: Bone marrow failure
· High: Hemolysis, Acute blood loss
2. Platelets
· Low: 50,000
ITP: Idiopathic thrombocytopenic purpura
o Splenomegaly
o Platelet antibodies
TTP: Thrombotic thrombocytopenic purpura
o Fever
o Neurologic symptoms (transient)
o Hematuria
§ Also BUN & Creatinine ↑
o Microangiopathic hemolytic anemia
o Low platelets
Others
o Myelofibrosis
o DIC
o Other microangiopathic hemolytic anemias
· High: 850,000
Essential thrombocytosis Jack II mutation: Polycythemia vera
Inflammation
CML
3. Calcium
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
· Normal: 8.5-10.5 mg/dl
1. PTH ↑
Primary hyperparathyroidism
Secondary hyperparathyroidism
2. PTH ↓
Malignancy
o Myeloma
o Breast
o Lung squamous cell
Hyperviaminosis D
Granulomatous disease
Drugs
o Tamoxifen
o Thiazides
3. Bone destruction
Hyperparathyroidism
Tumors
Multiple Myeloma
4. Osteoblastic lesions
Paget’s Disease of bones
Metastatic bone diseases
5. VITAMINS TRAP
Vitamin D
Immobilization
Thyrotoxicosis
Addison’s disease
Milk alkali syndrome
Inflammatory disorders
Neoplasms
Sarcoidosis
Thorizides
AIDS
Paget’s disease/Parathyroid disease
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CLINICAL LAB MEDICINE Formatted by Mark Tuttle 2010
- Albumin
o Normal range (adult): 3.1 – 4.3 g/dl
o Albumin ↓
· Not making it: Liver failure
· Not intaking it: Starvation/malabsorption
· Losing it
Urine: Nephrotic syndrome
Stool: Protein losing enteropathy
Burns
Third space: Ascites
- Myocardial infarction
o 2 hours: Myoglobin ↑↑ peak @ 12 hrs
o 4-6 hours
· Troponins – remain elevated for days