Renal

Question 1

Normal GFR

Answer 1

◦ Normal is 90-110 ml/min/1.72 m2

Question 2

serum creatinine

Answer 2

◦ Late marker of renal disease
◦ Inversely related to GFR
◦ Decreased filtration, increased serum creatinine
◦ Inversely and logarithmically related to creatinine clearance

Question 3

GFR

Answer 3

◦ Best overall index of kidney function
◦ How much volume the glomerular capillaries are filtering to the Bowman’s capsule per minute

Question 4

• Cystatin C

Answer 4

o Novel marker: more sensitive than SCr to detect early kidney disease

Question 5

• BUN/Creatinine

Answer 5

o Typically between 10:1 and 20:1
o Can provide clues to the underlying cause of the kidney dysfunction
 If increased suggests decreased renal blood flow, dehydration (pre-renal)
 If decreased can indicate liver disease, malnutrition, muscle injury

Question 6

• Creatinine

Answer 6

o Waste products of the breakdown of creatinine by muscles
o Most creatinine is filtered out by the kidneys
o Serum creatinine:
 Used in calculation of GFR
 As kidney function is impaired, serum creatinine will rise
o Urine creatinine:
 Typically measured over 24 hours
 Used to measure creatinine clearance

Question 7

• BUN

Answer 7

o Waste products formed in the liver during protein metabolism

Question 8

creatinine clearance

Answer 8

◦ How much blood plasma the kidney is clearing of creatinine
◦ By product of muscle metabolism, excreted by kidneys
◦ Can be estimated using equations but 24 hr urine more accurate
◦ Compare serum and 24h urine
◦ NL values by sex, age (pedi)

Question 9

GFR vs creatinine clearance

Answer 9

◦ Creatinine clearance can be used to estimate GFR but often overestimates it
◦ GFR is preferred measure of renal function

Question 10

Cystatin C

Answer 10

◦ Novel biomarker
◦ Protein produced by all body cells
◦ Filtered by healthy kidneys
◦ Persons with kidney damage will have elevated levels of Cystatin C
◦ May see elevation prior to decrease in GFR
◦ Less affected by muscle mass, age, sex or race
◦ No guidelines as to when this should be measured

Question 11

◦ FENa: Fractional Excretion of Na

Answer 11

◦ % of Na filtered by kidney

Question 12

◦ Differentiate pre-renal Acute Kidney Injury ( AKI) vs Acute Tubular Necrosis (ATN)

Answer 12

◦ <1%= AKI (pre-renal)
◦ >2%= ATN

Question 13

Dipstick Urinalysis: indications

Answer 13

◦ Concern for infection, calculi, malignancy or systemic kidney disease
◦ Not recommended for routine screening

Question 14

Dipstick Urinalysis: benefits

Answer 14

◦ Inexpensive
◦ Rapid results
◦ Easy to obtain

Question 15

dipstick urinalysis: recommendations

Answer 15

midstream, clean-catch sample
◦ Sometimes a first void specimen is preferred
◦ Examine within 2 hours or refrigerate
◦ If high suspicion for infection, advise use of wipes before sample

Question 16

Expected UA findings

Answer 16

◦ Nitrites: byproduct of bacteria metabolism
◦ Good indicator there is bacteria in the urine -> send for culture
◦ If symptomatic likely treat for UTI
◦ Asymptomatic bacteriuria: may not need to treat unless pregnant, DM
◦ Can be false positive if patient taking Pyridium (now OTC)
◦ Leukocyte esterase: produced by neutrophils in response to bacteria
◦ May also be seen in women if contamination from vagina flora
◦ Symptomatic -> send for culture
◦ RBCs: may be seen due to inflammation of the bladder/urethra
◦ Repeat UA after UTI treatment to ensure resolved
◦ Controversy re: treating UTIs over phone without culture
◦ Ideally check UA C+S before starting antibiotics
◦ Calculi:
◦ RBC’s typically present, due to irritation of blood vessel walls
◦ if not present, calculi unlikely
◦ Always rule out infection as well if RBCs present
◦ Consider pyelonephritis
◦ can co-exist with calculi
◦ may have similar pain with fever, flank pain and more severe s/s)
◦ Preferred imaging is noncontrast CT
◦ can also use ultrasound, sometimes KUB
◦ Always check renal function to look for obstruction

Question 17

Other common UA findings

Answer 17

• Glucose:
  o If elevated find out what patient recently ate
  o Consider POCT BS to assess for DM
• Ketones:
  o In diabetics more concerning for DKA
  o Ask about Keto diet if healthy, non-DM
• Specific Gravity:
  o Useful if concerned about dehydration or diabetes insipidus
• Bilirubin/urobilinogen
  o May read positive on dipstick if urine dark
  o Will be discussed more in next GI lecture

Question 18

Proteinuria (Albuminuria)

Answer 18

◦ Increased excretion of urinary albumin
◦ Marker of Kidney Damage
◦ Used in diagnosis of chronic kidney disease
◦ Can be measured on dipstick urinalysis
◦ Negative, Trace, 1-3+
◦ Not sensitive for small amounts of albumin
◦ More accurate is albumin/creatinine ratio
◦ 24 hour calculation is gold standard
◦ However, spot urine collection and analysis results correlate well and are generally used in practice

Question 19

hematuria

Answer 19

◦ Red Blood Cells
◦ Reported on UA as trace, small, moderate, large
◦ Common false positive on dipstick
◦ Commonly seen with UTI, contamination, menses, vaginitis

Question 20

Urine Culture and Sensitivity

Answer 20

◦ Positive culture is >100,000 colonies
◦ Depending on symptoms may consider >50,000 colonies positive
◦ May show contamination: small numbers of multiple bacteria,”mixed flora” or few than 10,000 colonies
◦ Most UTIs are treated empirically with antibiotics – most do not require C+S to be sent
◦ Cultures should be sent routinely in children with UTI s/s

Question 21

when to send in adults?

Answer 21

◦ Risk for resistant, severe infection
◦ Recurrent infection
◦ Complicated infection, concern for pyelonephritis
◦ Unsure of diagnosis

Question 22

Acute Kidney Injury: defined as

Answer 22

◦ Increase in Serum Creatinine by > 0.3 mg/dl within 48 hours
◦ Increase in Serum Creatinine to > 1.5x baseline presumably within prior 7 days
◦ Urine volume < 0.5 ml/kg/hr for 6 hours

Question 23

acute kidney injury: causes

Answer 23

◦ Pre-renal: poor blood flow to the kidney
- Intravascular volume depletion
- Decreased circulating blood volume GI bleed-
- Intrarenal vasoconstriction caused by meds, hemodynamic changes, vasodilation
◦ Intrinsic causes: damage to various parts of the kidney
◦ Ischemia -> ATN
◦ Infection, inflammation, thrombosis, nephrotoxins
◦ Post-renal causes: Obstruction of urinary flow
◦ Extrarenal: BPH, prostate cancer, masses
◦ **Intrarenal: **stones, clots, masses

Question 24

chronic kidney disease

Answer 24

◦ Presence of kidney damage or decreased kidney function for 3 or more months
◦ Either of the following are present for > 3 months
◦ Decreased kidney function as measured by GFR
◦ GFR <60

Question 25

◦ Kidney damage measured by:

Answer 25

◦ Albuminuria
◦ Urine sediment abnormalities
◦ Imaging abnormalties
◦ Abnormal pathology (biopsy)
◦ History of kidney transplant

Question 26

who should be screened?

Answer 26

◦ Hx DM or HTN
◦ Other Risk factors for CKD:
◦ CVD, HF, Older Age, Obesity, Family hx CKD, low birth weight, hx transplant
◦ Consider screening: no specific recommendations
◦ Screening of asymptomatic adults not recommended

Question 27

Cystoscopy

Answer 27

◦ Insertion of a cystoscope (camera) in the urethra
◦ Allows for visualization of bladder lining
◦ Biopsies can be taken as needed
◦ Done in urology office for evaluation of hematuria, recurrent UTI, incontinence, interstitial cystitis, strictures, stones, polyps, fistulas, congenital abnormalities
◦ Can also be done therapeutically to treat urethral strictures, remove stones, polyps
◦ Risks: perforation, infection
◦ Expect blood in the urine post-procedure
◦ 1x dose of prophylactic abx may be given

Question 28

prostate specific antigen (PSA)

Answer 28

◦ Secreted by epithelial cells of the prostate
◦ PSA is an enzyme…
◦ Liquefies semen to mobilize sperm
◦ PSA is not a unique identifier for prostate CA
◦ Low sensitivity, specificity
◦ Non-Cancer prostate conditions can elevate PSA
◦ Inflammation…
◦ BPH, for example
◦ May have prostate CA in the absence of elevated PSA
◦ 50-60% of those with localized, potentially curable CA have increased PSA
◦ Pts with less well-differentiated prostate CA actually have low PSA values (as low as 1 ng/mL)

Question 29

PSA testing

Answer 29

◦ Recommended against by AAFP
◦ PSA causes over-diagnosis of prostate tumors… with significant risks of biopsy/treatment
◦ Weigh risk vs benefit, shared decision making