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GU1 - Nephrology > Lab Med: renal fn and UA > Flashcards

Lab Med: renal fn and UA Flashcards

1
Q

Overview of kidney function

A
  • 180 L/d plasma filtered
  • 3L total plasma volume
  • Urine excretion 1-2 L/day
  • 99% of filtered plasma is reabsorbed
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2
Q

clearance def

A

volume of plasma from which a measured amount of substance X can be eliminated into the urine per unit of time

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3
Q

what does clearance depend on

A
  • plasma concentration of X

- excretory rate which is dependent on GFR which is dependent on renal plasma flow

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4
Q

what factors affect GFR

A
  • age: each decade after 20s lose about 4 mL/min GFR
  • race: AA diff
  • sex: females about 90% GFR of male
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5
Q

BUN

- what does it measure

A
  • urea

- liver converts ammonia (byproducts of aa/nitrogen metabolism) into urea

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6
Q

what is problem with using BUN to measure kidney function

A
  • 40% of BUN that is filtered is reabsorbed in PCT

- clearance of kidney based on BUN will underestimate GFR by about 40%

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7
Q

Creatinine

A

produced at a relatively constant rate, has stable blood levels, not influenced by diet

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8
Q

Problem with using Cr to measure kidney function

A
  • some that is filtered is secreted from PCT so that when get to urine, about 20% of urinary Cr came from tubular secretion not filtration
  • clearance of kidney based on Cr will overestimate GFR by about 20%
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9
Q

why choose Cr over BUN to measure kidney function?

A

BUN is dependent on nitrogen metabolism and is influenced by meat consumption and body’s metabolism of other aa.

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10
Q

examples of people who will have low BUN and high BUN

A

Low: cachectic, anorexic, bulimic

High: love to eat steak, lots of muscle, renal issues, can’t get rid of BUN

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11
Q

Formula to calculate simple Cr clearance

A

(Urine creatinine/plasma creatinine)(volume)

mL/min

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12
Q

formula for corrected creatinine clearance

A

Clcr uncorrected X 1.73/BSA

corrected for body surface area, takes body size into consideration

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13
Q

Most advanced formula for creatinine clearance

A

(140-age)(wt in kg) / (72)(plasma creatinine)

  • Now corrected for age (major impact)
  • Can multiple by 0.85 to adjust for female sex
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14
Q

BUN/Cr ratio

A

Dr. McNeill doesn’t use this

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15
Q

How does change in Cr affect GFR?

A

For every double of Cr (from 1 to 2), GFR reduces by half

ex: Cr from 1 to 2, normal GFR drops from 120 to about 60

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16
Q

Azotemia

A

elevation in BUN

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17
Q

Three major ways to cause azotemia

A
  • pre-renal
  • renal
  • post-renal
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18
Q

Pre-renal azotemia

A
  • Concentration of urea in the blood presented to the kidneys exceeds tea ability of the kidneys to eliminate it
  • Either bc the quantity of urea is increased OR renal blood flow is not sufficient to filtrate (decreased GFR)
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19
Q

causes of pre-renal azotemia

A
  • excess protein intake (last night’s steak)
  • acute cardiac decompensation
  • hemorrhagic shock
  • severe dehydration
    (fluid loss, lower pressure to renal arteries, lower GFR, less urea removal)
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20
Q

causes of renal azotemia

A
  • ATN
  • glomerulonephritis
  • pyelonephritis
  • damage to kidney reduces vascular supply to kidney
    (damage to glomerulus prevents filtration of urea from blood)
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21
Q

causes of post-renal azotemia

A
  • ureteral or urethral obstruction dt stone, tumors, strictures
  • prostatic obstruction
    (obstruction “backs up” urea elimination)
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22
Q

Azotemia vs. uremia

A
  • uremia is a condition

- azotemia is elevation of urea, not a condition

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23
Q

what sign can be seen in pt with high uremia?

A

uremic frost - friable white crystals on face

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24
Q

Urinalysis

- clean catch

A
  • wipe with cleansing cloth (not alcohol wipe)
  • catch mid-term to avoid “all the crap at the bottom of the bladder”
  • women much harder to get clean catch, men pretty easy
  • anticipate slight vaginal contaminant
  • hard to get if menstruating
  • bag can be used for infant/toddler
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25
Q

how to get clean catch on menstruating female?

A

quickcath - test tube with tiny catheter

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26
Q

Urine

  • how long at room temp
  • freezing?
A
  • good for two hours at room temp, refrigerate after that

- never freeze

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27
Q

Two components of urinalysis

A
  1. Dipstick: qualitative with quantitative properties
  2. Microscopic: use if positive dipstick, spin in centrifuge, draw off supernatant and re-suspend to look under microscope
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28
Q

How much blood does it take to make urine look bloody??

A

NOT very much

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29
Q

TNTC means what

A

Too numerous to count

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30
Q

What drug is commonly used in UTIs that renders UA useless?

A

Pyridium (Azo), orange color stains urine, have to wait about 24 hours to clear system before UA will work

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31
Q

What are the 10 tests on a UA dipstick

A
  1. leukoctes
  2. nitrite
  3. urobilinogen
  4. protein
  5. pH
  6. Blood
  7. specific gravity
  8. Ketone
  9. bilirubin
  10. glucose
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32
Q

Leukocytes on UA

A
  • does not test for whole WBC
  • tests for enzyme contained in granules of segmented neutrophils called esterase
  • when WBC are lysed, releases esterase, this happens when WBC sit in urine for awhile
  • NL = negative
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33
Q

What does it mean if 1+ UA esterase and 0 WBC in microscopic analysis?

A

NOT a UTI

34
Q

Nitrites on UA

A
  • NL = negative
  • Many common g. neg urinary bacteria (E.Coli) convert nitrate to nitrite
  • Used to CONFIRM UTI, not diagnose it as some bacteria don’t make nitrite
35
Q

+ leukocytes and + nitrites on UA means likely have what

A

UTI (94% sensitive)

36
Q

pH on urinalysis

A
  • NL: 4.5 to 7.0
  • <7 is acidic, many causes
  • > 7 is alkolotic, many causes
  • mostly worthless per Dr. McNeill
37
Q

What environment do E. coli prefer?

A

Alkaline or neutral pH. One way to help with UTIs is to create acidic urine. Citrus drinks like OJ or cranberry juice

38
Q

Blood urinalysis

A
  • NL = negative
  • Measures hemoglobin not RBC, must be lysed to be counted, can come from glomerulus to urethra
  • Male: NL always negative
  • Female: trace blood (and esterase) tolerable
  • Elevated in AGN, renal cell/bladder CA, stones, UTI, infection
39
Q

If a female pt has sx of UTI, 2-3+ UA blood, and is on menstrual period, can use UA to diagnose?

A

No… menstrual blood is possibly the cause of the positive UA blood… Either treat based on sx OR cath for clean blood

40
Q

Specific gravity UA

A
  • NL: 1.010 to 1.020
  • Measures concentration of urine (weight/density/unit volume)
  • Outside NL range not necessarily pathology!
  • Helps understand kidney’s ability to concentrate urine (osmolality is more accurate but SG is easier to measure)
41
Q

Specific gravity UA

Difference between osmolality and specific gravity

A
  • Osmolality looks at # of particles which determine the oncotic pressure
  • SG looks at the weight of particles
  • Na+ atom and albumin contribute the same to osmolality but very different contribution to specific gravity
42
Q

Specific gravity <1.010

A
  • dilute urine

- renal problems: kidney’s not able to concentrate urine like diabetes insipidus (lack ADH)

43
Q

Specific gravity >1.020

A
  • concentrated urine
  • dehydration
  • v/d
  • DM
44
Q

Glucose UA

A
  • NL = negative
  • Glucose into urine when blood glucose levels exceed reabsorption capacity of kidney
  • Usually when bs > 180
  • Almost always caused by diabetes (rarely low renal threshold for sugar)
45
Q

What is common in UA for pregnant women

A

Spill glucose and protein

46
Q

Ketones UA

A
  • NL = negative

- Seen in acidotic states

47
Q

Metabolic states that cause ketones in UA

A
  • DKA
  • Pregnancy (eclampsia)
  • Hyperthyroidism
  • Fever
48
Q

Dietary disorders that cause ketones in UA

A
  • starvation/fasting
  • vomiting/diarrhea
  • high fat diet
  • anorexia
49
Q

Protein UA

A
  • NL = negative
  • Tests for albumin
  • Need 24 hour collection for accuracy but not gonna happen in real life
  • Protein can come from a few places: blood, renal disorders that damage glomeruli, reabsorption defect in tubules
50
Q

What can cause false positive in protein UA

A

Bence-Jones of multiple myeloma

  • plasma cells produce IgG
  • part of protein breaks off and ends up in urine
  • if 70 yo man comes in with heavy proteinuria, MM should be high in DDX… (xray pelvis and electrophoresis on protein in urine next steps)
51
Q

Microalbuminuria

  • pathologic level
  • what level leads to 1+ on dipstick, why important
A
  • 30 to 300 mg/day pathologic

- >30 is 1+ on dipstick, indication have pathology

52
Q

What is considered normal renal function on a UA dipstick

A
  • NL Cr
  • Neg proteins (means kidney is filtering)
  • NL specific gravity (means kidneys are concentrating appropriately)
53
Q

Bilirubin on UA dipstick

A
  • NL = negative
  • Will only ever see conjugated bilirubin in urine (unconjugated is not water soluble, can’t pass through glomerulus)
  • If positive, need to evaluation for liver dysfunction and biliary obstruction
54
Q

Urobilinogen dipstick UA

A
  • NL: 0.2 – 1.0
  • Increased: hemolysis, hepatocellular dz
  • Decreased: abx (no ability to create from conjugated bili), bile duct obstruction
55
Q

What is urobilinogen

A

End product of conjugated bilirubin after it has passed through the bile ducts and metabolized in the intestines

56
Q

Know the cycle of bilirubin

A

learned this in GI

57
Q

Microscopic UA

- list 10 items

A
  • WBC (actual cells)
  • RBC (actual cells)
  • Casts and type
  • crystals
  • yeast
  • epithelial cells and type
  • trichomonas
  • bacteria
  • color
  • clarity
58
Q

How would blood in the urine be presented on microscopic UA?

A
  • WBC: 8-13 or so
  • RBC: TNTC
    This is the normal composition
59
Q

How would pus in the urine be presented on microscopic UA?

A

RBC and WBC are TNTC

60
Q

Color in urine microscopy

A
  • NL = clear
  • too clear: DM, high fluid intake, caffeine, ETOH, diuretics
  • concentrated: dehydration
  • orange: high bilirubin, pyridium
  • green: pseudomonas
  • brown/yellow/”tea” colored: increased bilirbuin
  • pink/red: RBC, hemoglobin
61
Q

Clarity in urine microscopy

A

NL = clear

cloudy/turbid: abnormal particles (WBC, RBC, bacteria, mucus)

62
Q

Epithelial cells in urine microscopy

A
  • squamous contamination from vaginal lining
  • > 10 is too much contamination to use the sample…
  • if see other types like cuboid, transitional requires further workup (bladder or endometrial ca or damage)
63
Q

Bacteria in urine microscopy

A
  • can indicate infection
  • bc bacteria are abundant normal microbial flora in vagina and external urethral meatus it is common in urine specimens
  • should be interpreted in view of clinical sx
64
Q

WBC in urine microscopy

A
  • NL: 2-3
  • Pyuria: >3
  • indicates inflammation or infection
65
Q

what is sterile pyuria?

A
  • WBC without bacteria

- indicates chronic urethritis, prostatitis, interstitial nephritis

66
Q

RBC in urine microscopy

A
  • NL: 2-5
  • hematuria: >5
  • commonly from menses
67
Q

Non menses causes of hematuria

A
  • RBCs from renal and GU system trauma
  • UTI, tumor, stone, glomerulonephritis, pyelonephritis, smokers, exercise, polycystic kidneys
  • dysmorphic RBC: suggests glomerular bleeding
68
Q

Casts in urine microscopy

A
  • cylindrical structures formed by intratubular precipitation of protein
  • cells can be trapped within matrix of protein
69
Q

List the 5 types of casts

A
  • Hyaline
  • RBC
  • Leukocyte
  • Fatty
  • Waxy
70
Q

What are the two casts that can be normal

A
  • hyaline

- waxy

71
Q

Hyaline casts

A
  • can be normal
  • might indicate need for further w/u
  • seen in concentrated urine, fever, exercise
72
Q

RBC casts seen in what

A

glomerulonephritis

73
Q

WBC casts seen in what

A
  • infection (pyelonephritis)
  • inflammation (interstitial nephritis)
  • more related to the CD, could be UTI that works its way from bladder up to the CD in the kidney (ouch)
74
Q

Fatty casts seen in what

A
  • nephrotic syndrome (heavy proteinuria)
75
Q

Crystals in urine microscopy - 5 types

A
  1. magnesium ammonium phosphate
  2. uric acid - acidic urine, gout*
  3. calcium phoshate - alkaline urine
  4. calcium oxalate - ethylene glycol poisoning
  5. sulfur - sulfa drugs
76
Q

What causes magnesium ammonium phosphate crystals in urine?

A
  • proteus mirabilis
  • infects kidneys, forms triple phosphate
  • condenses and forms stone that fills entire renal pelvis and calyxes!
  • “Staghorn calculus” or “struvite”
77
Q

Table 7-19

A

Review

78
Q

Hemolytic jaundice

  • serum total bilirubin
  • serum conjugated bilirbuin
  • urine urobilinogen
  • urine conj. bilirubin
  • stool
  • skin
A
  • increased
  • normal/slight elevation
  • normal
  • absent
  • brown (nl)
  • jaundice
79
Q

biliary obstruction

  • serum total bilirubin
  • serum conjugated bilirbuin
  • urine urobilinogen
  • urine conj. bilirubin
  • stool
  • skin
A
  • increased
  • increased
  • absent
  • present
  • clay-colored
  • jaundice
80
Q

Intrahepatic cell damage

  • serum total bilirubin
  • serum conjugated bilirbuin
  • urine urobilinogen
  • urine conj. bilirubin
  • stool
  • skin
A
  • increased
  • decreased (damaged cells don’t conjugate) OR increased (cells conjugate but can’t be secreted)
  • decreased
  • present if conjugating
  • brown to clay colored
  • jaundice
81
Q

Urine C and S

A
  • > 100,000 colony forming units is pathogenic, enough bacteria to cause UTI
  • mixed flora gen means have vaginal contaminant
  • takes about 48 to get back, often start empirical tx and adjust therapy based on results if necessary

GU1 - Nephrology (16 decks)

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