Lab Interpretation Flashcards
Sensitivity
The ability to correctly identify who HAS a disease
Specificity
The ability to correctly identify who does NOT have the disease
Positive Predictive Value
Proportion of positive tests that are truly positive. Also referred to as the “precision rate.” Proportion of positive tests that are truly positive.
Negative Predictive Value
Number of true negatives out of all people who test negative.
Complete Blood Count (CBC)
White Blood Cell (WBC) Red Blood Cell (RBC) Hemoglobin (HgB) Hematocrit (HcT) Mean Corpuscular Volume (MCV) Mean Corpuscular Hemoglobin (MCH) Mean Corpuscular HgB Concentration (MCHC) Red Cell Distribution Width (RDW) Platelets (PLT)
CBC Fishbone
WBC // Hemoglobin / Hematocrit // PLT
White Blood Cell Count…
WBC is sensitive… but non-specific!
Elevated due to infection, acute stress, air pollution, medications, leukemias
Depressed: yellow fever, amebiasis
“You know something is wrong somewhere, but it doesn’t give you the full clinical picture”
White Blood Cell Differential
Takes more time, and may be more expensive…
Ordered when CBC count is elevated
Differential Count: Basophils (0.5 - 1%) Eosinophils (1-4%) Neutrophils (40-60%) Monocytes (2-8%) Lymphocytes (20-40%)
Differential % always equal 100%.
Absolute Differential
WBC count by % of cell type
Basophils
Least common of all the WBCs
Increase in response to same conditions that cause increased eosinophils
Release histamine, bradykinin & serotonin activated by injury or infection
Medications - increase: antithyroid therapy / decrease glucocorticoids, antonioplastics
Eosinophils
Defend against parasitic infection
Part of the allergic response
Often found in sputum of patients with asthma
Medications that increase eosinophils: Digoxin, Heparin, PCN, Propanolol
Medications that decrease it: corticosteroids
Neutrophils
Most numerous WBC but most short-lived
Increased production during acute stress
Types:
Banded/”Bands” –> Immature (5%)
Segmented/”Segs” –> Mature (95%)
Left Shift: Increased # of bands (immature). When someone is acutely ill, body will respond by producing more baby neutrophils
Causes of Neutrophilia
Bacterial infection
Medications: Lithium, Steroids, Heparin
Cigarette Smoking
Obesity
Causes of Neutrophilia
Bacterial infection
Medications: Lithium, Steroids, Heparin
Cigarette Smoking (increased # of ‘segs’)
Obesity (increased # of ‘segs’)
Monocytes
Produced by Marrow –> Circulates 5-8 days –> Enter tissue and becomes histiocyte
Not common in circulating blood
Lymphocytes
2nd most numerous WBC
Main function: immune response
T & B cells
Medications that decrease lymphocytes: glucocorticoids, immunosuppressants
Lymphocytes (continued)
Elevated: mononucleosis, TB, pertussis, influenza
Depressed: AIDS, Aplastic Anemia, MS, GBS. Medications that cause depression: steroids
Leukocytosis
Usually due to neutrophils of lymphocytes
of neutrophils increases the severity of infection
Total WBC count reflects quality of immune system
% of Neutrophils…
Indicates severity of infection
Total WBC…
Reflects quality of immune system
Leukocytes Scenario #1
25 yo with pneumonia
Total WBC = 18,000
Neutrophils = 60% (10,800)
Moderate infection with good immune response!
Leukocytes Scenario #1
25 yo with pneumonia
Total WBC = 18,000
Neutrophils = 60% (10,800)
Moderate infection with good immune response!
Leukocytes Scenario #2
85 yo with pneumonia
Total WBC = 11,500
Neutrophils = 80% (9,200)
Bands = 10%
Severe infection with poor immune response
Leukocytes Scenario #2
85 yo with pneumonia
Total WBC = 11,500
Neutrophils = 80% (9,200) // Normal is 40-60
Bands = 10%
Severe infection with poor immune response
Red Blood Cells (Erythrocytes)
Produced in bone marrow. Stimulated by erythropoietin.
Lifespan: 120 days
Anemia: at least a 10% decrease in RBC
Decreased RBC caused by:
(1) Increased destruction of RBC
(2) Decreased production
(3) Blood loss
Increased RBC: Polycythemia
Primary
Secondary: Lung & Heart disease, High altitude, tobacco use
Decreased RBC caused by:
(1) Increased destruction of RBC
(2) Decreased production
(3) Blood loss
Increased RBC: Polycythemia
Primary. Likely an enlarged spleen, liver. May present with DVT, or hypertension
Secondary: Lung & Heart disease, High altitude, tobacco use. Hypoxia is the thing that drives this
Hemoglobin & Hematocrit
HCT: Total volume of RBCs relative to volume of whole blood
3 variables: fluid volume, RBC size, RBC count
*Useful only if pt is euvolemic
HGB: pain portion fo RBCs
1/3 of the HCT value
Sex-dependent; age-dependent. Adults have higher value than children. Men have higher values than women.
Hemoglobin & Hematocrit
HCT: Total volume of RBCs relative to volume of whole blood
3 variables: fluid volume, RBC size, RBC count
*Useful only if pt is euvolemic
HGB: pain portion fo RBCs
1/3 of the HCT value
Sex-dependent; age-dependent. Adults have higher value than children. Men have higher values than women.
Hemoglobin increased when the RBC # increases
MCV - Mean Corpuscular Volume
Will look at when evaluating someone for anemia
Measures the volume and average size of RBCs
Q: What is the most common cause of microcytic anemia? –> Iron deficiency
Anisocytosis
RBCs are of unequal sizes
MCH
Measurement of HGB in the RBC
Divide HGB by the RBC
Helps find the source of anemia
MCHC
Measure how tightly hemoglobin is paced in RBC
Red Cell With Distribution (RDW)
Volume variation in size of RBCs. Increased variation in size - reticulocytosis (higher in patients who have had some kind of bleed).
Platelets
Smallest formed elements in blood
Important for blood clotting and homeostasis
Increased in myeloproliferative disorders
Decreased: heparin, lupus
Von Willibrans Disease
Normal # of platelets, but don’t have the ability to stick together
CASE STUDY #1
Dx: Aspiration pneumonia
(1) Parkinson’s - often have dysphagia
(2) Crackles to right lower lobe (aspiration, usually right lobe)
High WBC, high neutrophils
BUN is quite elevated (28) –> likely dehydration
Infiltrate is not showing up because dehydration
What is her prognosis and why?
Look at WBC count, neutrophil % (and segs, bands)
She has a pretty significant infection. Her neutrophils are at 77% (normal range is 40-60%)
WBC is 16,000 - that is OK, is managing a good response
Basic Metabolic Panel
Glucose / BUN / Creatinine / CO2 / Potassium / Sodium / Calcium / Chloride
Comprehensive Metabolic Panel
BMP elements (above) PLUS Protein, Albumin, LFTs
LFTs are AST (SGOT), ALT (SGPT), ALK PHOS, Bilibunin
Why order a Metabolic Panel?
(1) Volume Status - response to interventions and fluid
(2) Renal and Liver status
(3) Monitor electrolytes
Caution…
SSRIs can cause hyponatremia
Albumin
Has never seen a high albumin level
Low albumin is caused by kidney disease, liver disease, undernutrition, Crone’s Disease
Be careful when prescribing Warfarin
Thyroid Panal
TSH and Free T4 for screen (Free T4 not affected by the amount of protein in someone’s blood)
ESR
Crude measurement of inflammation (over 100, likely a serious underlying disease).
BNP
Released primary from the heart. When there are high filling pressures, this is secreted (will be higher when patient is having heart failure exaccerbation).
