Wk 1 important stuff

Question 1

Differentiate between accuracy and precision

Answer 1

1) Accuracy: The “trueness” of a test
-How well does it measure what it claims to measure
2) Precision: Reproducibility of a test
-How close with the result be if repeated on the same patient/sample

Question 2

1) What kind of test does not miss positive cases, but might be positive for other things?
2) What kind of test may give a negative result when the disease is present?

Answer 2

1) Sensitive tests
2) Specific tests

Question 3

Differentiate between false positives and false negatives

Answer 3

1) False positive: Test is positive, condition is not present
2) False negative: Test is negative, condition is present

Question 4

Differentiate between prevalence and incidence (definitely on quiz)

Answer 4

1) Prevalence: proportion of people who have a condition during a time period
-All cases present during that time (regardless of when it began)
2) Incidence: proportion of people who develop a condition during a time period
-Only new cases that occurred during that time

Question 5

List the general principles of lab tests

Answer 5

1) No test is perfect
2) Even high-quality labs can be wrong, be willing to recheck surprising results
3) Reference ranges can vary from one lab to the next
4) Degree of abnormality is useful
5) Avoid excessive repetition of tests
6) Avoid shotgun ordering
7) Will this test alter the management or provide relevant information

Question 6

Once kidney disease is discovered, what needs to be established?
2) What is the most useful initial study?
3) True or false: GFR doesn’t explain the cause of kidney disease

Answer 6

1) The degree of disease
2) Estimated glomerular filtration rate (GFR) and examination of the urinary sediment
3) True

Question 7

1) Define GFR
2) Normal GFR is the sum of what?

Answer 7

1) Rate at which fluid is filtered through the kidneys
-Volume of fluid filtered through glomerular capillaries into the Bowman’s capsule over time
2) All filtration rates in all the functioning nephrons; varies considerably even among normal individuals

Question 8

1) Declining GFR indicates what?
2) Is this exactly correlated with nephron loss?
3) Why is this important?

Answer 8

1) Declining GFR indicates kidney dysfunction
2) No, bc kidneys attempt to compensate by adjusting filtration through remaining/normal nephrons
3) Stable GFR doesn’t imply stable disease & normal GFR doesn’t mean there isn’t underlying renal disease

Question 9

1) True or false: Losing 50% of kidney mass means losing 50% of normal GFR

2) True or false: Stable GFR doesn’t imply stable disease
Normal GFR doesn’t mean there isn’t underlying renal disease

Answer 9

1) False; losing 50% of kidney mass doesn’t mean 50% normal GFR
2) True

Question 10

1) What are 3 characteristics of a good filtration marker?
2) What if these 3 criteria are met?
3) True or false: Filtration markers can be expensive, difficult to obtain, and their administration can be complex

Answer 10

1) Freely filtered at the glomerulus, neither secreted nor reabsorbed by the tubules, and not changed during the process
2) The filtered amount is equal to the excretion rate
3) True

Question 11

1) In most settings, we estimate GFR through doing one of what two things?
2) What exists in steady state in body (if diet and muscle mass are stable)?

Answer 11

1) Measuring creatinine clearance or applying various equations to the serum creatinine value
2) Creatinine

Question 12

1) Where does creatinine come from? (3 places)
2) What are 3 characteristics of creatinine?
3) Name a disadvantage of using it for GFR

Answer 12

1) Creatine metabolism in skeletal muscles, ingested meat, & kidney/liver produce it.
2) Freely filtered, not absorbed, not metabolized
3) Need to account for muscle mass (& overestimates GFR)

Question 13

1) 10-40% of urinary creatinine is from what?
2) Does creatinine overestimates or underestimate GFR? By how much?
3) Higher muscle mass means does what to SCr (serum creatinine)?

Answer 13

1) Tubular secretion
2) Overestimates 10-20% (acceptable)
3) Higher SCr given the same rate of clearance

Question 14

Give and explain the formula for GFR

Answer 14

GFR = UV / P
U = creatinine concentration of urine that was collected over 24 hours
V= volume of urine (expressed as mL/min)
P= serum creatinine concentration

Question 15

1) What type of person with CKD (chronic kidney disease) may have the same SCr as a young healthy male? Why?
2) Urine collections over smaller windows give ___more/less___ accurate results [regarding creatinine clearance (CC, CrCl)]

Answer 15

1) Older female; muscle mass
2) less

Question 16

There are various equations derived from demographic data that can be useful for measuring CrCl (and therefore, eGFR) without the need for urine collection; when are they not an accurate GFR measure?

Answer 16

Where GFR is changing rapidly (AKI)

Question 17

Recap:
1) CrCl estimates GFR using ___________ as a filtration marker
2) Decreased CrCl suggests ____increased/decreased____ filtration which suggests _______ dysfunction.
3) Increased CrCl can occur with what?

Answer 17

1) creatinine
2) decreased; kidney
3) High cardiac output (HTN, CHF, even exercise)

Question 18

1) Define Blood Urea Nitrogen (BUN)
2) Where is urea formed? From what?
3) Is urea superior or inferior to creatinine as a filtration marker?

Answer 18

1) Measures the amount of urea nitrogen in the blood
2) In the liver as the end product of protein metabolism
3) Inferior to creatinine

Question 19

1) What excretes urea?
2) When does urea increase? What disease can affect it?
3) 40-50% of it is reabsorbed where?

Answer 19

1) Kidneys
2) Increases with ingested protein; liver disease
3) Proximal tubule

Question 20

1) BUN/Cr Ratio is useful in calculating what?
2) What do both have in common? Which has variable reabsorption? Which is minimally reabsorbed?

Answer 20

1) Renal function
2) Both freely filtered by glomerulus; BUN (in tubules); creatinine

Question 21

1) What may cause an increased BUN/Cr ratio? (2 things)
2) What may cause a decreased ratio? (1)

Answer 21

1) BUN reabsorption is disproportionately elevated relative to Cr
OR
Renal hypoperfusion, dehydration, heart failure
2) Reduced reabsorption of BUN

Question 22

1) Define Chronic Kidney Disease
2) What is it characterized by?
3) WNL GFR is what?

Answer 22

1) Group of disorders characterized by changes in kidney structure and function
2) Presence of kidney dysfunction/damage for 3 months
3) 90-120

Question 23

Acute Kidney Injury (AKI) types are divided according to cause; list & define the 3 categories

Answer 23

1) Prerenal: issue with blood flowing to kidney
2) Intrarenal (renal, intrinsic): disease process in the kidney
3) Postrenal: urinary tract obstruction

Question 24

1) List potential causes of prerenal issues with blood flow to kidney (prerenal)
2) List potential causes of disease processes in the kidney (intrarenal (renal, intrinsic))
3) List potential causes of urinary tract obstruction (postrenal)

Answer 24

1) CHF, renal artery stenosis, dehydration, cirrhosis, etc.
2) Glomerulonephritis, acute tubular necrosis, acute interstitial nephritis, etc.
3) Kidney stones, BPH, cancer, obstructed catheter, etc.

Question 25

1) What can you use to help differentiate between causes of acute kidney injury?
2) What does this tool use?

Answer 25

1) A table of predicted lab values to help guide clinical approach into these numerous causes
2) Uses BUN/Cr, urine concentration of sodium, urine osmolality, and fractional excretion of sodium (calculation that measures Na excreted vs Na reabsorbed)

Question 26

Takeaways:
1) _______ is used to estimate GFR and therefore evaluate kidney disease
2) Direct measurement is difficult; indirect measurement still involves _______________.
3) Equations estimate GFR using what?

Answer 26

1) CrCl
2) 24hr urine.
3) sCr

Question 27

Takeaways:
1) CrCl is not useful in acute settings so _________ is used instead. Use reference table
2) True or false: Declining GFR means declining renal function. Improving GFR means improving kidney function
3) Where does creatinine come from?

Answer 27

1) BUN/Cr
2) True
3) Ingested meat and skeletal muscle metabolism etc

Question 28

Takeaways:
1) If factors affecting CrCl are _____________ , CrCl is less useful in estimating GFR
2) Higher skeletal muscle means __________ CrCl without kidney dysfunction
3) True or false: Other filtrate markers can be used if Cr is disrupted by diet or disease.

Answer 28

1) unstable
2) higher
3) True

Question 29

True or false: Creatinine =/= creatine

Answer 29

True

Question 30

Which accurately detects the presence of a disease (i.e. positives are really positive), a sensitive test or a specific test?

Answer 30

Specific (rules things in)

Question 31

Which rules conditions out, sensitive tests or specific tests?

Answer 31

Specific

Question 32

A test saying someone is pregnant when they’re not is an example of what type of error?

Answer 32

Type I (false positive)

Question 33

Give an example of a type 2 error

Answer 33

A pregnancy test giving a false negative (i.e. test is negative but pt is pregnant)

Question 34

Currently, the _____________ of measles is low, but we’re keeping an eye for any increasing ________________

Answer 34

prevalence; incidence

Question 35

The straight leg raise (SLR) test has __high/low__ sensitivity and __high/low__ specificity. What does this imply?

Answer 35

high; low
A positive test doesn’t strongly suggest you have HNP, but you can trust that negatives are true negatives

Question 36

Name one lab value that’s tied to both liver and kidney function

Answer 36

BUN

Question 37

List each stage of chronic kidney disease and its accompanying GFR. Describe each and what your treatment should be.

Answer 37

1) Stage 1: >/_90, kidney damage w. normal or ^ GFR.
2) Stage 2: 60-89, kidney damage w. mildly decreased GFR
-1&2: Dx underlying etiology if possible, treat comorbid conditions, estimate progression and try to slow it.
3a) 45-59, mild-moderate decreased GFR
3b) 30-44, moderate-severe decreased GFR
-3s: same as above
4) 15-29
-Prep for end-stage renal disease
5) <15 (or dialysis)
-Dialysis, transplant, or palliative care