Diagnosis by Lab Methods

Question 1

sensitivity

Answer 1

rate of true positive of test

very sensitive - always positive for someone who has disease

good negative predictive value

if positive - can’t conclude they have disease

Question 2

specificity

Answer 2

good positive predictive vale

positive specific test - 100% certain have disease

negative - doesn’t mean they don’t have disease

Question 3

tests with high specificity

Answer 3

used to CONFIRM results of sensitive, but less specific screening test

Question 4

incidence

Answer 4

number of new cases of disease in specified period

divided by size of population under consideration who were initially disease free

measure of RATE

Question 5

prevalence

Answer 5

actual number of cases during period of time or at particular date in time

measure of COMMONALITY

Question 6

chronic incurable disease

Answer 6

low incidence but high prevalence

Question 7

highly contagious, rapidly fatal disease

Answer 7

high incidence, but low prevalence

Question 8

work up in chest pain labs

Answer 8

• serum lactate DH
• serum creatinine phosphokinase
• serum myoglobin
• serum troponin

Question 9

1975

Answer 9

galen first use if CPK, LD, and isoenzymes

Question 10

1985

Answer 10

CK MB

Question 11

1991-1992

Answer 11

troponins

Question 12

lactate DH

Answer 12

LDH
-enzyme catalyzes coversion of lactate to pyruvate

cells die - release LDH to blood

seen in many different cells

not good predictive value

Question 13

good thing about LDH

Answer 13

stays high in serum for long time

useful in someone with bad chest pain 36 hours ago
-may still be elevated

hemolysis also causes elevation of LDH-1
-NOT THAT SPECIFIC

Question 14

CPK

Answer 14

catalyzes reversible transfer of P between creatinine and phosphocreatine as well as between ATP and ADP

BB - brain
MB - cardiac
MM - skeletal m

Question 15

sensivitiy/specificity of CPK-MB

Answer 15

> 90%

within 7-18 hours

quicker and more specific

Question 16

CPK relative index

Answer 16

mass of CPK-MB fraction / total CPK x 100

ratio less than 3 - skeletal m source

ration grater than 5 - cardiac source

Question 17

myoglobin

Answer 17

O2 binding in muscle tissue

sensitive test - but not enough

levels rise early after muscle damage

elevated 2-4 hours after symptoms, peak 6-12 hours, normal 24-36 hours

Question 18

temporal changes in CK-MB and myoglobin

Answer 18

myoglobin rapid increase

CK - MB - less rapid increase

Question 19

troponin

Answer 19

regulatory protein in striated muscle

calcium channels open - Ca causes troponin to change shape allowing actin and myosin to bind leading to contraction

three subunits
-TnC - binds Ca
TnT - binds tropomyosin
TnI - binds actin

Question 20

troponin levels

Answer 20

gold standard for determining myocardium damage

Question 21

serum troponin levels

Answer 21

increase 3-12 hours after onset of chest pain, peak 24-48 hours, return to baseline 5-14 days

criterion standard*** for diagnosing myocardial infarction

Question 22

troponin C

Answer 22

same all muscle tissue

Question 23

troponin I and T

Answer 23

cardiac specific

-these ones used

Question 24

78yo F - weak and dizzy, HTN, lethargic, mucous membrane pale, murmur, lungs CTA

Answer 24

anemic

Question 25

work up for anemia

Answer 25

blood loss - most common marrow - decreased production hemolysis - destruction iron deficiency - most common etiology

Question 26

most common cause of anemia

Answer 26

blood loss

Question 27

lab tests for anemia

Answer 27

``` RBC count peripheral smear serum iron total iron binding serum ferritin retic count RBC distribution ```

Question 28

elevated bilirubin

Answer 28

hemolysis

Question 29

CBC

Answer 29

give you indices - MCV - MCHC - chronic iron deficiency anemia - both below normal range after blood loss - cellular indices do not enter abnormal range until after most erythrocytes destroyed (120 days)

Question 30

anemia

Answer 30

ranked basis of size and Hg content microcytic hyperchromic -and others **know this

Question 31

microcytic hypochromic erythrocytes on peripheral smear

Answer 31

chronic iron deficiency anemia

Question 32

folate and iron deficiency

Answer 32

common in areas of world with little fresh meat and produce peripheral smear - population of macrocytes** mixed among microcytic hypochromic cells can normalize the MCV

Question 33

sickle cell anemia

Answer 33

see on peripheral smear not rounded and concave - RBCs misshaped - looked like sickles doesn't hold O2

Question 34

Dx of iron deficiency

Answer 34

- low serum iron and ferritin - elevated TIBC normal serum ferritin - deficienct in iron with coexistent diseases hepatitis or anemia of chronic disorders

Question 35

red blood cell indices

Answer 35

do not become abnormal for several moths after tissue stores are depleted of iron

Question 36

hemoglobin studies

Answer 36

Hg A2 and fetal Hg - electrophoresis - measure of Hg A2 and fetal Hg - useful for establishing beta-thalassemia or Hg C or D as etiology of microcytic anemia

Question 37

reticulocyte Hg content

Answer 37

and serum iron are only parameters independently associated with iron deficient anemia

Question 38

stool testing

Answer 38

Hg in stool - GI bleed very common etiology for anemia

Question 39

absence of stainable iron in bone marrow aspirate**

Answer 39

permits establishment of diagnosis of iron deficiency without other lab tests

Question 40

61yo M - ICU, repair of ruptured aneurysm, lost blood, transfused, urine output has been slowing

Answer 40

oliguria

Question 41

oliguria

Answer 41

diminished capacity to form and pass urine less than 500mL in 24 hours imbalance of body fluids / electrolytes renal disease urinary tract obstruction

Question 42

prerenal failure

Answer 42

hyaline and fine, granular casts observed on urinalysis increased specific gravity

Question 43

renal failure

Answer 43

hematuria and proteinuria are prominent -brown granular casts are typically found in ischemic or toxic acute tubular necrosis

Question 44

acute interstitial nephritis

Answer 44

white cells in urinalysis eosinos and white cell casts

Question 45

postrenal

Answer 45

obstruction

Question 46

prerenal

Answer 46

high specific gravity high urine:plasma Cr low urine sodium low FENa hypovolemia**

Question 47

renal

Answer 47

urine:plasma Cr osmolality ratio 40 FENa >2 intrinsic renal disease**

Question 48

BUN/Cr

Answer 48

>20:1 prerenal <20:1 renal failure Cr - varies with age lose 50% of kidney function - may not have change in serum Cr

Question 49

serum Na

Answer 49

useful in diagnosis cause of oliguria

Question 50

hyponatremia

Answer 50

fluid retention, administration of hypotonic fluid

Question 51

hypernatremia

Answer 51

secondary to dehydration

Question 52

serum K

Answer 52

oliguria - decreased GFR - reduced tubular secretion - metabolic acidosis - increased serum potassium

Question 53

0.1 reduction in arterial pH

Answer 53

raises serum potassium by 0.3

Question 54

reasons for ordering lab test

Answer 54

diagnosis** monitor screen research

Question 55

shotgun-ordering

Answer 55

large number of lab tests that may or may not have adequate diagnostic predictive value in identifying particular disease

Question 56

rifle-ordering**

Answer 56

specific lab tests based on assessment of their diagnostic accuracy and predictive value in identifying a particular disease

Question 57

how will test results influence patient management?

Answer 57

important question before ordering a lab test