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PCM III > interpretation of clinical lab tests > Flashcards

interpretation of clinical lab tests Flashcards

1
Q

if a test is highly sensitive, it means?

A
  • test result is negative you can be nearly certain that the patient does not have the disease
  • high rate of true negatives
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2
Q

highly sensitive tests are used to ______ for disease

A

screen

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3
Q

if a test is highly specific, it means?

A
  • test result is positive you can be nearly certain that patient actually has disease
  • high rate of true positives
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4
Q

highly specific tests are used to _____ for disease

A

confirm the results of sensitive

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5
Q

validity

A

measure of the test’s ability to indicate which individuals have the disease and which do not

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6
Q

reliability

A
  • another term for consistency

- if test is admin repeatedly, does it yield the same results

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7
Q

incidence

A
  • the number of new cases of a disease or condition in a specified time period divided by the size of the population under consideration who were initially disease free
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8
Q

incidence is a direct measure of?

A

disease risk - high incidence implies higher risk

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9
Q

prevalence

A
  • actual number of cases alive with the disease either during a period of time (period prevalence) or at a particular date in time (point prevalence)
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10
Q

period prevalence vs point prevalence

A
  • period prevalence provides better measure of the disease load since it includes all new cases and all deaths between 2 dates
  • point prevalence only counts those alive on a particular date
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11
Q

low prevalence rate means

A

a lot of ppl die from the disease or the disease is cured fairly quickly

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12
Q

high prevalence rate means

A

a lot of ppl live with the disease

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13
Q

screening test is used to?

A

identify an asymptomatic individual who may have a particular disease

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14
Q

diagnostic test is sued to?

A

confirm the presence of a disease when a subject shows signs or symptoms of the disease

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15
Q

common screening tests

A
  1. pap smear
  2. fasting blood cholesterol
  3. fasting blood sugar
  4. BP
  5. fecal occult blood
  6. ocular pressure
  7. PKU test
  8. TSH
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16
Q

lab tests to workup for chest pain

A
  1. serum lactate dehydrogenase level
  2. serum creatinine phosphokinase level
  3. serum myoglobin levels
  4. serum troponin levels
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17
Q

lactate dehydrogenase

A
  • an enzyme that catalyzes the conversion of lactate to pyruvate
  • as cells die, their LDH is released and finds its way into the blood
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18
Q

lactate dehydrogenase levels in MI

A
  • total LDH level rises within 24-48 hrs after an MI, peaks in 2-3 days, and returns to normal in 5-10 days
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19
Q

lactate dehydrogenase sensitivity and specificity for MI

A

diagnostic sensitivity and specificity is more than 90% within 24 hours of an MI when LDH-1 >40% of total; however even slight hemolysis can cause non-diagnostic elevations in LDH-1

20
Q

creatinine phosphokinase

A

CPK enters blood rapidly following damage to mm cells but CPK levels rise and fall rapidly with a variety of other circumstances

21
Q

sensitivity and specificity of CPK-MB for MI

A
  • sensitivity and specificity of CPK-MB for MI are >90% within 7-18 hrs; peak concentrations occur within 24 hours and return to normal within 2-3 days
  • sensitivity is poor when total CPK is very high
  • specificity is poor when total CPK is low
22
Q

myoglobin sensitivity for MI

A

not sensitivity enough to use for negative predictive value

23
Q

troponin in dx MI

A
  • criterion standard for dx MI
  • higher specificity for MI than CK-MB
  • higher long-term sensitivity than LD-1
24
Q

troponin subunits seen in MI

A

cTnI and cTnT (troponins I and T)

25
Q

lab test is useful in identifying the etiology of _____

A

anemia

26
Q

CBC documents the ___ of the anemia

A

severity

27
Q

what is shown on a CBC in chronic iron deficiency anemia?

A

mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) have values below normal range

28
Q

when will CBC enter abnormal range during blood loss?

A

CBC will not enter abnormal range until most of the RBC produced before the bleed are destroyed at the end of their normal lifespan (120 days)

29
Q

what will be seen on a peripheral smear in chronic iron deficiency anemia?

A
  • microcytic and hypochromic RBC

- microcytosis is apparent in the smear before the MCV is decreased

30
Q

how can MCV normalize?

A
  • macrocytes mixed among the microcytic hypochromic cells

- occur in areas with folate and iron deficiency due to little fresh produce and meat

31
Q

what is diagnostic of iron deficiency?

A

low serum iron and ferritin levels with an elevated TIBC

32
Q

more sensitive laboratory indicators of mild iron deficiency

A

serum ferritin and stainable irone in tissue stores

33
Q

how long before RBC indices become abnormal after tissue stores are depleted of iron?

A

several months

34
Q

how is stool testing used in dx iron deficiency anemia?

A

hemoglobin in the stool is useful in establishing GI bleeding as etiology of iron deficiency anemia

35
Q

how can bone marrow aspirate be diagnostic of iron deficiency?

A

absence of stainable iron in bone marrow aspirate permits establishment of a dx of iron deficiency w/o other lab tests

36
Q

definition of oliguria

A

diminished capacity to form and pass urine -

37
Q

UA findings in prerenal failure

A
  • few hyaline and fine, granular casts
  • little protein, heme, or red cells
  • specific gravity of urine increased
38
Q

UA findings in intrinsic renal failure

A
  • hematuria and proteinuria are prominent
  • broad, brown, granular casts found in ischemic or toxic acute tubular necrosis
  • red cell casts found in glomerulonephritis
  • white cells, especially eosinophils and white cell casts in acute interstitial nephritis
39
Q

what is often used to distinguish decreased GFR from intrinsic renal disease?

A

fractional excretion of sodium

40
Q

BUN/Cr in pre-renal and renal failure

A

pre-renal: >20/1

renal:

41
Q

why is serum creatinine unreliable as indicator of renal damage?

A
  • serum creatinine vary with age, lean mm mass, and hydration status
  • serum levels may not change until >50% of kidney fx has been lost
  • at lower GFR, increased tubular secretion of creatinine can lead to overestimation of renal fx
42
Q

serum sodium is useful in dx ____?

A

cause of oliguria since urine output is influenced by serum sodium

43
Q

hyponatremia usually indicates? hypernatremia usually indicates?

A
  • hyponatremia is usually dilutional secondary to fluid retention or admin of hypotonic fluids
  • hypernatremia is usually secondary to dehydration
44
Q

how is serum potassium related to oliguria?

A

oliguria -> decreased GFR -> reduced tubular secretion -> metabolic acidosis -> increased serum potassium (decreased arterial pH raises serum potassium)

45
Q

4 legitimate reasons for ordering a lab test

A
  1. dx
  2. monitoring
  3. screening
  4. research
46
Q

approach to ordering lab tests

A
  1. shotgun - ordering a large number of lab tests that may or may not help in dx a particular disease
  2. rifle - ordering a specific lab tests based on how helpful it is in identifying a particular disease

PCM III (13 decks)

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