Introduction to Diagnostic Medicine: Basic Labs and Imaging

Diagnostic vs Screening

diagnostic:
proof to presence/absence of disease
results provide a dx
ex: abdominal/pelvic CT with PO+IV contract→acute appendicitis

screening:
detect potential disease indicators
results→further testing+confirmation
ex: mammogram
colonoscopy

Sensitivity vs Specificity

Sensitivity:
the proportion of true positives correctly identified by the test
-If someone has the disease, how likely is the test to correctly detect it?

Example:
If a COVID test has 95% sensitivity, it correctly detects 95 out of 100 infected people (but misses 5)

Mnemonic:
👉 “SnNout” — a SeNsitive test, when Negative, rules OUT disease (because it rarely misses cases)

Specificity:

Definition:
The proportion of true negatives correctly identified by the test
-If someone does not have the disease, how likely is the test to correctly say they’re disease-free?

Example:
If a pregnancy test has 98% specificity, it correctly reports “not pregnant” for 98 out of 100 non-pregnant people (but gives 2 false positives)

Mnemonic:
👉 “SpPin” — a SPecific test, when Positive, rules IN disease (because it rarely gives false positives).

False Positive vs False negative

false positive: test says that there is a disease when there is not
ex: pt doesn’t fast before serum glucose→positive result

false negative: test says that there is no disease when there is
ex: positive COVID/pregnancy test but no actual disease

Precision vs Accuracy

Accuracy:

Medical definition:
How close a measured or observed value is to the true or accepted reference value

• Accuracy = Correctness

• A test is accurate if its results are on average correct

Example:
If a blood glucose meter consistently reads 100 mg/dL when the true glucose level is 100 mg/dL, it’s accurate.
If it reads 110 mg/dL or 90 mg/dL, it’s inaccurate (biased).

Precision:
How consistent or reproducible the test results are when repeated under the same conditions

• Precision = Consistency

• A test is precise if repeated measurements give similar results, even if those results are not correct

Example:
If a blood glucose meter gives readings of 110, 111, and 109 mg/dL for the same sample, it’s precise (results cluster together),
but if the true value is 100 mg/dL, it’s not accurate.

Importance of Different Collection Tubes in Clinical Setting

Prevent clotting or promote clotting depending on the test

Preserve certain components (cells, plasma, serum, or specific analytes)

Ensure accurate test results by using the right additive/anticoagulant

Facilitate separation of blood components during centrifugation

Avoid chemical interference in lab assays

Complete Blood Count (CBC) (General)

series of tests that determine blood cells’:
-number
-variety
-percentage
-concentrates
-quality

DX:
WBC
WBC diff
RBC
platelets

WBC Reference Range

hemoglobin:
male (15+y/o): 13.0-17.0 g/dL
female (15+y/o): 11.5-15.5 g/dL

hematocrit:
male: 40-55%
female: 36-48%

platelet count normal range:
adult: 150,000-400,000/mL

white blood cell (WBC) normal range:
adult: 5,000-10,000/mL

White Blood Cells (WBCs)

total number of white blood cells→leukocytes

up→leukocytosis
usually caused by one type of leukocyte

E: leukemia
trauma
toxins
drugs (epinephrine)
hemorrhage
post splenectomy

down→leukopenia

E: viral infections
bone marrow depression
primary bone marrow disorders:
-leukemia
-pernicious/aplastic anemias

WBC With Differential

differential (diff) WBC count→percentage of each type of WBC

neutrophils

eosinophils

basophils

lymphocytes

monocytes

Neutrophils

most numerous of WBCs

respond to inflammation→primary defense→phagocytosis

“bands”: immature nucleus appearance

“left shift”: more immature than mature neutrophils in blood

ex: “rise in bands with a left shift"

Eosinophils

respond to allergic+parasitic states

contain histamines

up: eosinophilia

E: allergies
asthma
chronic skin disease
random→black widow spider bites

down: eosinopenia

E: Cushing’s syndrome (acute adrenal failure)
acute bacterial infections+significant left shift

Basophils

contain heparin+histamines+serotonin

not found in blood in a normal state→rarely seen in healthy bone marrow

mast cells: tissue (not blood) basophils

Monocytes

phagocytosis→removed injured+dead cells from circulating blood

Lymphocytes

involved in immunologic reactions

T cells:
CD4
CD8

B cells:
control body’s antigen-antibody response
contain “memory”→can attack same pathogens again

up: lymphocytosis

E: lymphatic leukemia
infections mononucleosis→dx with presence of atypical lymphocytes (picture)
CMV
acute HIV infection

down: lymphopenia

E: chemotherapy
immunosuppressant mx
AIDS

Red Blood Cells (RBCs)

aka erythrocytes

carries hemoglobin→O2+CO2 transfer

increased: polycythemia
-chronic low O2 saturation

decreased: anemia
-bone marrow dx

Hematocrit (HCT)

RBC mass

the amount of RBCs

high: too many cells
-dehydration
-polycythemia
-heart dx

low: too few cells
-anemia
-leukemia
-blood loss

Hemoglobin (HGB)

transports O2+CO2 on the RBCs

hemoglobin concentration directly related to oxygen capacity

interfering factors:
altitude (higher (HGB)
lower with excessive fluid intake
pregnancy (both dilution issues)

Mean Corpuscular Volume (MCV)

individual cell size

normocytic: normal size

macrocytic: bigger than normal

microcytic: smaller than normal

Mean Corpuscular Hemoglobin Concentration (MCHC)

measures the concentration of hemoglobin in RBCs

important in monitoring therapeutic tx of anemia

Mean Corpuscular Hemoglobin (MCH)

weight of hemoglobin per RBC

dx of severely anemic pts

Stained Red Cell Examination (Peripheral Smear)

inspects:
size

shape

structure of RBCs

Platelet Count

aka thrombocytes

necessary for clotting

partially clotted blood effects results:

elevated platelet count: thrombocytosis
ex: splenectomy
iron deficient anemia
polycythemia
inflammatory dx
high altitude

decreased platelet count: thrombocytopenia
ex: ITP
pernicious
aplastic+hemolytic anemias
viral/bacterial infections
transfusions (dilution effects)

BMP vs CMP

BMP: basic metabolic panel
checks systems related to body’s metabolism (acid/base balance/serum glucose level/kidney function)

-Na
-K
-glucose
-Ca
-CO2
-chloride
-BUN
-creatinine

CMP: comprehensive metabolic panel
all functions of BMP+added tests to check liver function

all BMP tests+
-albumin
-alkaline
-phosphate
-ALT
-AST
-total bilirubin

Blood Urea Nitrogen (BUN)

measures quality of nitrogen in urea (waste product)

assesses glomerular function

increased:
CHF
dehydration
shock
stress
AMI
chronic renal dx
urinary tract obstruction

decreased:
liver fialure
malnutrition (low protein intake)
impaired absorption (Celiac disease)

Creatinine

byproduct of muscle breakdown

produced at a constant rate+excreted in kidneys

impaired kidney function→decreased excretion→elevated SCr level

increased:
impaired renal function
obstruction of urinary tract
CHF
shock
dehydration
rhabdomyolysis

decreased:
small stature
decreased muscle mass
advanced liver dx
pregnancy

Albumin

protein made by liver

maintains colloidal osmotic pressure in. vascular+extravascular spaces

keeps fluid in bloodstream+not leak out into other spaces

evaluates nutritional status

Bilirubin

byproduct of breakdown of hemoglobin in RBCs/hemolysis

removed from body by liver+excreted into bile (gives bile it’s color)

normal: small amount in serum samples

excessive destruction of RBS/liver cannot excrete normally→increase

Alkaline Phosphatase

aka alk phos

enzyme found throughout whole body

large amount+other PE findings→liver/bone problem

ex: jaundice+increased alk phos→liver problem

Aspartate Transaminase/Alanine Transaminase (AST/ALT)

aspartate transaminase (AST):
found in tissues with high metabolic activity
cell injury/death→released

alanine aminotransferase (ALT):
found mostly in liver (liver inflammation)
aLt=LIVER
liver cells damage→released

Urinalysis List

color

odor

turbidity

specific gravity

pH

glucose

ketones

blood

protein

bilirubin

nitrite

leukocyte esterase

other abnormalities revealed by microscopic examination

Urinalysis: Color+Odor

color:
normal→clear-light yellow
dehydration→dark yellow-brown

odor:
acidic nature→faint odor
DM: ketosis→fruity odor (acetone)
UTI: bacteria splits urea→ammonia→foul smell

Urinalysis: Turbidity

normal: clear

turbid: cloudy

Urinalysis: Specific Gravity

kidney’s ability to concentrate urine

measure of dissolved chemicals (minerals/salts)

low:
diabetes insipidus (loss of ADH→low SG+large urine volume)
glomerulonephritis
pyelonephritis

high:
DM
dehydration
CHF

Urinalysis: pH