Lab Medicine Flashcards
4 Disciplines of Lab Medicine
- hematology
- chemical pathology
- microbiology
- immunology
What types of clinical reasoning go into doing labs?
- why test is being ordered
- what are consequences of not ordering a lab test
- how good is the test at differentiating health from disease
- how are the test results interpreted
- how will the test results influence patient management
Reference Range
- comparison of a patient’s laboratory test result vs. a reference or “normal” range
- for some analytes, the range is defined as less than or greater than a certain value
What must be considered when using reference range to interpret a patient’s lab results?
- age
- gender (eg pregnancy if applicable)
- lab and technique used
- situational: geographic, fasting vs nonfasting, medications
Gaussian Distribution
- a bell-shaped curve where the central 95% is typically used as a test’s normal range
- normal range encompasses mean plus or minus 2 SD
- roughly 5% of normal patients may be outside the cutoff value
Screening Test
-identifies asymptomatic people who may have a disease
Diagnostic Test
-determines presence or absence of disease when patient shows signs or symptoms
What are some common disease screenings?
- pap smear for cervical cancer
- fecal occult blood test for colorectal cancer
- PSA tests for prostate CA
- PPD test screens for TB
- mammography for breast CA
Validity
-how well a test distinguishes between who has disease and who does not
Reliability
- consistency of test at different times or under different conditions
- degree to which results are free from random error
Sensitivity
- measures validity of test
- disease oriented
- ability to identify those WITH disease correctly
- minimizes false negatives
- SNOUT: sensitivity test with negative results rules out disease
- # of true positives/(true positives + false negatives)
Specificity
- healthy oriented
- ability to identify those without disease correctly
- minimizes false positive
- SPIN: specific test with positive result rules in disease
- # of true negatives/(true negatives + false positives)
Principle Function of Circulating Blood
transportation
Principle Function of RBCs
transport hgb, which carries O2
Principle Function of WBCs
involved in defending your body from foreign invaders
Principle Functions of Platelets
respond to blood vessel injury to form a clot
Indications for Ordering a CBC
- investigate disease of blood or bone marrow
- investigate response to inflammation or infection
- assess sxs of fatigue, pallor, weakness, unexplained bleeding or bruising, dizziness, fever, weight loss
What components are included in CBC?
- WBC count
- RBC count
- Hgb
- Hematocrit
- MCH, MCHC, MCV
- RDW
- platelets
Normal RBC Range
- male 4.73 - 5.49 10^6/ uL
- female 4.15 - 4.87
Mean Cellular Volume
- Normal Value
- Define
- 78-98 um^3
2. average volume of RBCs; useful in classifying type of anemia
- Increase in Mean Cellular Volume
2. Decrease in Mean Cellular Volume
- increase MCV = vitamin B12 or folic acid deficiency
2. decrease MCV = iron deficiency anemia
Hemoglobin
- male: 14.40 - 16.60 gm/deciliter
- female: 12.2 - 14.7 gm/deciliter
Hematocrit
- proportion of blood that is made up of RBCs
- percentage of RBC/total blood volume
- men 40-54%
- women 37-47%
Causes of Elevated Hgb
- loss of plasma volume (dehydration)
- high altitude
- smokers with COPD
- congenital heart disease
Causes of Low Hgb
- increased destruction of RBCs
- decreased production of RBCs
- blood loss
- pregnancy
- vitamin deficiency
WBCs
-normal: 4500-11000 cells/mm^3
- Granulocytes
2. Agranulocytes
- neutrophils, eosinophils, basophils
2. lymphocytes, monocytes
Neutrophils/PMN
- 40-76%
- elevated in bacterial infections, inflammatory conditions
Basophils
- 0-1%
- elevated CML, after splenectomy, polycythemia
- decreased rheumatic fever, pregnancy, steroid therapy, radiation therapy
Eosinophils
- elevated with allergic or parasitic infection, skin disease
- NAACP: neoplasma, allergy/asthma, Addisons disease, collagen vascular disease, parasites
Lymphocytes
- 24-44%
- elevated with viral infection
Monocytes
- 3-7%
- elevated with phagocytosis bacterial infections
Causes of Elevated WBCs
- acute bacterial or viral infections
- leukemia
- post splenectomy
- steroids (prednisone)
- may occur w/o disease: high stress, excitement, pain, trauma, heat)
Causes of Low WBCs
- viral infections
- overwhelming bacterial infections
- hypersplenism
- medications that suppress bone marrow
- bone marrow suppression
Platelets
- 150,000-400,000/mm^3
- avg life span 7-10 days
Causes of Low Platelets
- enlarged spleen
- platelet destruction
- decreased platelet production
- alcoholism
Causes of Elevated Platelets
- hemorrhage
- splenectomy
- inflammation
Urinalysis
- assist in identifying urologic conditions: stone, UTI, malignancy
- assist in identifying systemic disease
- midstream, clean catch
Urinalysis: Clarity
-cloudy: bacteria, blood, crystals
Urinalysis: Odor
- foul smell with infection (e. coli)
- sweet smell with diabetes (ketones)
Urinalysis: Color of Urine
- red: hematuria, kidney stones, UTI, bladder cancer
- yellow: dehydration, foods
- orange: medication side effects
- brown: glomerulonephritis, myoglobin
Specific Gravity
- 1.001-1.035
- elevated with volume depletion
- decreased with excessive fluid intake, diabetes insipidus, diuretic therapy
pH
- 4.6-8.0
- increased with vomiting, some urinary disease, or kidney disease
- decreased with aspirin overdose, starvation, alcohol ingestion, high protein diet
Urinalysis - Protein
- proteins too large to pass through glomerulus
- associated with glomerulonephritis, pre-eclampsia, screen for complications from DM
Urinalysis - Glucose
- serum levels above 150-300 will produce glucose in urine
- associated w/ DM, burns, pancreatitis, corticosteroid use, Cushing’s disease
Urinalysis - Ketones
- ketones formed from breakdown of stored fat
- associated with starvation, alcoholism, or diabetic ketoacidosis
Urinalysis - Bilirubin
- by-product of hemolysis
- associated w/ biliary obstruction and liver injury
Urinalysis - Blood
-associated w/ kidney stones, urinary trauma, UTI, strenuous exercise or bladder cancer
Urinalysis - Leukocyte Esterase
- detects enzymes released by WBCs
- associated with UTI
Urinalysis - Urobilinogen
- bilirubin may react with bacteria in gut to produce urobilinogen
- associated w/ hemolysis and hepatocellular disease
Urinalysis - Nitrites
- some bacteria convert nitrates to nitrites
- positive result = UTI usually
Microscopic Urinalysis Exam
- urine microscopic requires centrifuged sample
- requires lab tech to look for WBC, RBC, proteins, casts
- WBC: 0-5 per high power field
- RBC: 0-3 per high power field
Microscopic Urinalysis - Proteins
-associated w/ multiple myeloma
Microscopic Urinalysis - Crystals
- formed from solutes in the urine
- associated w/ kidney stones
Microscopic Urinalysis - Casts
- formed in distal convoluted tubule
- abnormal protein formed during infection of inflammation
- red cast: glomerulonephritis
- white cast: pyelonephritis
Liver Functions
- conjugate bilirubin
- synthesis of proteins and clotting factors
- involved in storage and disposal of nutrients, drugs, toxins
Liver Profile - Aspartate Aminotransferase
- 7-42 IU/liter
- elevated with liver, muscle, or cardiac injury
Liver Profile - Alanine Aminotransferase
- 1-45 IU/liter
- more sensitive with liver injury
Liver Profile - Alkaline Phosphatase
- normal 25-160 IU/L
- elevated with bile duct obstruction (cholecystitis, viral hepatitis, cirrhosis)
Liver Profile - Gamma glutamyl transpeptidase
- elevated with liver injury or biliary obstruction
- used as a marker of alcohol use
Unconjugated Bilirubin
- bilirubin bound by albumin
- not water soluble
- elevated with hemolysis
Conjugated Bilirubin
- bilirubin cleaved of albumin
- water soluble
- elevated with bile duct obstruction
Albumin
- protein made in liver
- marker of liver function
Indications for Ordering Coagulation Studies
- unexplained bleeding disorder or excessive bruising
- consecutive pregnancy loss
- patients receiving heparin or coumadin therapy
Prothrombin Time (PT)
- normal 11.5-13.5 seconds
- measure extrinsic pathway of coagulation
- time required for coagulation to occur
- marker of liver function
Partial Thromboplastin Time (aPTT)
- normal 27-38 seconds
- measures intrinsic coagulation pathway
- most commonly used to monitor heparin therapy
Pancreas Enzymes
amylase and lipase
Increased Levels of Amylase and Lipase Associated With?
- pancreatitis
- biliary obstruction
- pancreatic carcinoma
Amylase
- 10-130 U/L
- peaks earlier and declines more rapidly with pancreas inflammation
Lipase
- normal < 52 U/L
- lipase remains elevated longer
- lipase more specific for pancreatic inflammation
Electrolyte Function
- determine overall fluid status
- acid/base status
Indications for Ordering Electrolytes
- patients receiving IV fluid
- metabolic or endocrine abnormalities
- medications that interfere with electrolytes
- severe vomiting/diarrhea
Sodium
- 136-145 mmol/L
- major extracellular cation
- involved with maintenance of blood and body fluids and conduction of impulses
Elevated Sodium
- not enough water in body (dehydration)
- vomiting and diarrhea
- endocrine
Decreased Sodium
- overhydration
- endocrine (Cushing’s)
Potassium
- 3.5-5.0 mEq/L
- major intracellular cation
- involved in conduction of impulses
Elevated Potassium
- cell injury
- kidney failure
- endocrine (Addisons)
- can lead to arrhythmias
Decreased Potassium
- malnutrition
- vomiting, diarrhea
- diuretic medications
Elevated Chloride
- > 107 mEq/L
- dehydration
- overactive parathyroid glands
Decrease Chloride
- <97 mEq/L
- vomiting
Elevated Magnesium
- normal 1.3-2.1 mg/dL
- kidney disease
- use of antacids
Decreased Magnesium
- inadequate absorption (poor diet, alcoholism, diarrhea)
- medications like diuretics
Calcium
- normal 8.2-10.2 mg/dL
- most stored in bone 99%
- half in circulation is protein bound, other half ionized
- only ionized Ca is metabolically active
- important in muscle contraction, cardiac function, nerve impulse, blood clotting
Elevated Calcium
- hyperparathyroid hormones
- cancer
- excessive vitamin D
Decreased Calcium
- hypoparathyroid hormones
- deficient protein
- vitamin D deficiency
Glucose
- formed from carb digestion and conversion of glycogen to glucose by the liver
- insulin decreases blood glucose
- glucagon increases blood glucose
- fasting blood glucose (<110, impaired 110-125)
- elevated glucose may be sign of DM, endocrine disorders, prednisone therapy, pancreatitis
Hgb A1C
- normal <5%
- measures glycosylated hemoglobin
- reflects the average blood glucose [ ] over past 2-3 months
- useful in monitoring DM management
Blood Urea Nitrogen (BUN)
- normal 5-20 mg/dL
- urea is produced in liver as waste from protein breakdown
- urea has to be filtered by the kidneys and is excreted in urine
Elevated BUN
- impaired kidney function
- increased protein catabolism
- dehydration
Decreased BUN
- liver failure (less urea produced)
- malnutrition
- endocrine disorders
Creatinine
- normal 0.9-1.2 men and 0.6-1.1 women
- production is constant and correlates directly with muscle mass
- assesses renal function
Elevated Creatinine
- impaired renal function
- large muscle mass
Decreased Creatinine
- decreased muscle mass
- liver disease
Uric Acid
- normal 3.4-8.0 mg/dL men, 2.4-6 women
- end product of purine metabolism
- most uric acid is excreted by the kidneys
Increased Uric Acid
- excessive cell breakdown of nucleonic acids (gout)
- excessive destruction of cells (leukemia)
- inability to excrete uric acid (renal failure)
Thyroid Gland
- regulates metabolic activity
- involves interaction between hypothalamus, anterior pituitary, thyroid gland
TSH
- 0.4-4.8 mIU/L
- most sensitive test for screening thyroid disorders
- elevated = hyperthyroid
- decreased = hypothyroid
- T4
2. T3
- 0.8-1.7 ng/dL
- 80-200 ng/dL
elevated T4/T3 = hyperthyroid
decreased T4/T3 = hypothyroid
Cultures
- involve growing microorgs or living tissue cells on a special medium to support growth of the material
- allow specific microbial identification
- collected and performed prior to beginning abx therapy
Blood Culture
-when suspected bacteremia present
Urine Culture
-when suspected UTI or pyelonephritis
Throat Culture
-gold standard for strep pharyngitis
Sputum Culture
-dx and tx of pneumonia and TB
Sed Rate
-marker of inflammation
D-dimer
- marker of clotting process
- useful to screen for venous thrombosis (DVT)
Brain Natriuretic Peptide (BNP)
- hormone produced by ventricles of the heart
- increased with ventricular volume expansion and pressure overload
- increased with CHF
