14 - Interpretation of Lab Results Flashcards
Sensitivity
- A sensitive test is able to pick up affected persons
- Used to rule out diagnoses (used at an early stage of a diagnosis work-up)
- A sensitive test is most useful when negative (Interpretation according to the prevalence, Use of the negative predictive value)
Sensitive test example
Example: D-dimer
- Want it to be negative
- If it is negative, good, moving on
- If it is positive, need more testing
Specificity
- A specific test is able to pick up non-affected persons
- Used to rule in diagnoses
- Used to confirm a diagnosis suspected because of other data
- A sensitive test is most useful when positive
- Interpretation according to the prevalence
- Use of the positive predictive value
Specific test example
- Want it to be positive
- If it is negative, need a lot more testing
- If it is positive, you have a diagnosis
In order to RULE IN a diagnosis…
Use a specific test
Be careful before concluding if
- The disease is unlikely
- The test is not specific
In order to RULE OUT a diagnosis…
Use a sensitive test
Be careful before concluding if:
- The disease is common
- The test is not sensitive
Complete blood count
- Red blood cells (RBCs)
- Hemoglobin (Hgb)
- Hematocrit (Hct)
- Platelets
- White blood cells (WBCs)
CBC includes…
RBC Hgb Hct Platelets WBC
RBC indices…
MCV
MCH
MCHC
RDW
WBC differential
Bands Neutrophils Eosinophils Basophils Lymphocytes Monocytes
Hemoglobin
- The amount of hemoglobin present in the blood
- Men: 13-18
- Women 12-18
- Higher in smokers
- Lower in anemic, blood loss, overhydration
Hematocrit
- Percent of RBCs in the plasma
- Men: 37-49%
- Women: 36-46%
- High in dehydration, olycythemia
- Low in overhydration, anemia, blood loss
Look at recording
WBC
- Number of white blood cells per cubic millimeter of blood
- 4500-11000
- High in infection, leukemia, steroid use
- Low in viral infection, immunodeficiency
RBC
- Number of RBCs per cubic mm of blood
- Men: 4.5-5.3
- Women: 4.1-5.1
- High in polycytheia, high altitude
- Low in bone marrow suppression, loss of erythrocytes
MCV
- Mean corpuscular volume (size of RBC)
- Men: 78-100
- Women 78-102
- High in folic acid deficiency, B12 deficiency, alcoholism
- Low in iron deficiency anemia, lead poisoning
MCH
- Mean corpuscular hemoglobin (amount of hemoglobin present in one cell)
- 24-35
- High in folic acid deficiency, B12 deficiency
- Low in iron deficiency anemia, thalassemia
MCHC
- Mean corpuscular hemoglobin concentration (the proportion of each cell occupied by hemoglobin)
- 31-37%
- High in folic acid deficiency, B12 deficiency
- Low in iron deficiency anemia, thalessemias
RDW
- Red blood cell distribution width (calculated fromteh MCV and RBC)
- 11.5-14%
- High in iron deficiency, thalassemia minor
Bands
“Left shift”
- Percent of young/immature neutrophils
- Normal is 0-5%
- High in bacterial infection, severe stress
- Low in typhoid, tularemia, brucellosis, cancer, bone marrow depression
PMNs
- Percent of segmented or immature neutrophils
- 45-70% normal
- High in bacterial infection, severe stress
- Low in typhoid, tularemia, brucellosis, cancer, bone marrow depression
Eosinophils
- Percent of eosinophils present
- 0-8% normal
- High in allergies, parasites
- Low in corticosteroid therapy
Basophils
- Percent of basophils present
- 0-3% normal
- High in leukemia, not well understood
- Low in corticosteroid therapy
Lymphocytes
- Percent of lymphocytes present
- 16-46% normal
- High in viral infection, leukemia
- Low in AIDS, autoimmune disease
Monocytes
- Percent of monocytes present
- 4-11% normal
- High in tuberculosis, protozoa infection, leukemia
Peripheral blood smear
- A drop of blood is spread (smeared) on a slide and stained with a special dye and looked at under a microscope
- The number, size, and shape of red blood cells, white blood cells, and platelets are recorded
- Used to diagnose leukemia, malaria, SCD and others
Urinalysis
- Color
- Clarity
- Specific gravity (concentration of urine)
- pH
- Protein (first sign of kidney disease in diabetics)
- Glucose
- Nitrites
- Leukocyte esterase
- Ketones (type 1 diabetes, starvation)
Urine microscopy
- Red or white blood cells
- Casts
- Crystals
- Bacteria, yeast cells, or parasites
- Squamous cells (not a clean catch, need to repeat)
Serum electrolytes
- Na+
- K+
- Cl-
- HCO3-
- Mg2+
Sodium (Na+)
Normal = 135-145
Hypernatremia
- Dehydration
- Excess saline administration
- Exchange transfusion with stored blood
- Impaired renal function
Hyponatremia
- Overhydration
- Sodium loss (vomit, diarrhea)
- Increased renal sodium loss
Potassium (K+)
Normal = 3.5-5.0
Hyperkalemia
- Renal failure
- Excess K+ replacement
- Massive tissue damage
- Metabolic cidosis
Hypokalemia
- Diuretics
- Inadequate intake
- Large steroid doses
- Metabolic alkalosis
Chloride (Cl-)
Normal = 100-108
Just follows sodium
Bicarbonate (HCO3-)
Normal = 24-30
Base excess (metabolic alkalosis)
- Loss of gastric contents
- Diuretic use
Base deficit (metabolic acidosis)
- High bicarb consumption
- Loss of bicarbonate
- Increased chloride in serum
Magnesium (Mg2+)
Normal = 1.4-1.9
- Hypermagnesmia
- Hypomagnesemia
Blood glucose tests
- Fasting blood glucose (FBG)
- Random blood glucose (RBG)
- Oral glucose tolerance test (OGTT)
- Glycosylated hemoglobin (A1C)
Renal function tests
- BUN
- Creatinine
BUN
- Blood urea nitrogen
- Renal function test
- Normal = 8-25
- High levels indicate renal disease, renal damage, dehydration, shock, CHF, GI bleed, high protein diet
- Low levels indicate overhydration, increased ADH secretion
Creatinine
- Creatinine is a renal function tests
- Men: 0.6-1.4
- Women: 0.6-1.1
- High in kidney disease, renal toxic medications
- Low in low muscle mass, muscle atrophy
Liver function tests
- Aspartate aminotransferase (AST)
- Alanine aminotransferase (ALT)
- Alkaline phosphatase (ALP)
- Bilirubin
- Ammonia
Liver enzymes only tell you if there is a DIFFUSE problem with the entire liver
If there is a tumor taking up 90% of the liver, but 10% is still functioning normally, the liver enzymes will be normal
Fasting lipid panel
- Cholesterol
- Triglycerides
- HDL
- LDL
- VLDL
Cholesterol
Want less than 200
Triglycerides
Want less than 150
HDL
Positive cardiac risk factor
LDL
Negative cardiac risk factor
VLDL
Want 10-31
Amylase and lipase
- Diagnose pancreatitis
- Diagnose salivary gland obstruction
- Lipase is SPECIFIC for pancreatitis
This is included in an abdominal pain panel
Inflammatory markers
- C- Reactive Protein (CRP)
- Erythrocyte Sedimentation Rate (ESR)
C- Reactive Protein (CRP) is positive in…
- Chronic inflammation
- Chronic infection
- Auto-immune diseases
- Cardiovascular risk
Erythrocyte Sedimentation Rate (ESR)
- Chronic inflammation
- Chronic infection
- Auto-immune diseases
Cardiac markers
- Troponin T
- Troponin I
- Total CK
- CK-MB
- Myoglobin
- BNP
Troponin is the MOST specific
Time course for serum markers
- Troponin and CK-MB start to increase 3-12 hours after symptoms begin
- Troponin stays high for up to 10 days
- CK-MB stays high for only 36-48 hours
- LDH increasese 6-12 hours after symptoms begin and stays high for 6-8 days
- Myoglobin begins to increase 1-4 hours after symptoms begin and stays high for 24 hours
Helicobacter pylori tests
- Used to detect H. pylori infection in the stomach and duodenum
- H. pylori can cause peptic ulcers but most people with H. pylori do not develop ulcers
Blood antibody test for H. pylori
Positive Ab means either currently infected or have been in the past
Urea breath test for H. pylori
Positive means current infection
Stool antigen test for H. pylori
Helps support diagnosis
What is the ONLY iron study that is HIGH during iron deficiency anemia
** THIS IS IMPORTANT **
Total iron binding capacity - Transferrin level
What levels will be low in iron studies during anemia?
** THIS IS IMPORTANT **
All other tests
- Serum iron
- Ferritin (iron stores)
- Others
What test do you do to check the effects of warfarin?
** THIS IS IMPORTANT **
Prothrombin Time (PT/INR)
PT checks five clotting factors (I, II, V, VII and X)
INR standardizes the results of PTs regardless of testing method
What test do you do to check the effects of heparin?
**** THIS IS IMPORTANT *****
Partial thromboplastin time (PTT)
Prostate specific antigen
** THIS IS IMPORTANT **
Screening test for prostate cancer in men
- Increases normally as a man’s prostate enlarges with age
- May increase in prostatitis or prostate cancer
- An injury, a digital rectal exam, or sexual activity (ejaculation) may also briefly raise PSA levels
- Exercise will NOT increase PSA **
Arterial blood gasses
** THIS IS WHAT YOU NEED TO KNOW **
Respiratory acidosis
- pH is less than 7.35
- Caused by high PCO2
- Compensated by increasing bicarb
Respiratory alkalosis
- pH is higher than 7.45
- Caused by low PCO2
- Compensated by decreasing bicarb
Metabolic acidosis
- pH is less than 7.35
- Caused by low bicarb
- Compensated by decreasing PCO2
Metabolic alkalosis
- pH is higher than 7.45
- Caused by high bicarb
- Compensated by increasing PCO2
Thyroid tests
The hypothalamus releases thyrotropin-releasing hormone (TRH) which acts on pituitary to release thyroid stimulating hormone (TSH) which stimulates the thyroid gland to use iodine from food to make thyroxine (T4) and triiodothyronine (T3) needed for metabolism and energy production
TSH Free thyroxine (fT4) Triiodothyronine (T3).
Who’s at risk for vitamin B12 deficiency (cyanocobalamin)?
Strict vegetarians
Who’s at risk for folic acid/RBC folate (vitamin B9) deficiency?
Meat-only eaters (not enough green leafy vegetables)
