Lab Med: renal fn and UA Flashcards
(81 cards)
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
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
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
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
5
Q
BUN
- what does it measure
A
- urea
- liver converts ammonia (byproducts of aa/nitrogen metabolism) into urea
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%
7
Q
Creatinine
A
produced at a relatively constant rate, has stable blood levels, not influenced by diet
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%
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.
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
11
Q
Formula to calculate simple Cr clearance
A
(Urine creatinine/plasma creatinine)(volume)
mL/min
12
Q
formula for corrected creatinine clearance
A
Clcr uncorrected X 1.73/BSA
corrected for body surface area, takes body size into consideration
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
14
Q
BUN/Cr ratio
A
Dr. McNeill doesn’t use this
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
16
Q
Azotemia
A
elevation in BUN
17
Q
Three major ways to cause azotemia
A
- pre-renal
- renal
- post-renal
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)
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)
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)
21
Q
causes of post-renal azotemia
A
- ureteral or urethral obstruction dt stone, tumors, strictures
- prostatic obstruction
(obstruction “backs up” urea elimination)
22
Q
Azotemia vs. uremia
A
- uremia is a condition
- azotemia is elevation of urea, not a condition
23
Q
what sign can be seen in pt with high uremia?
A
uremic frost - friable white crystals on face
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
25
how to get clean catch on menstruating female?
quickcath - test tube with tiny catheter
26
Urine
- how long at room temp
- freezing?
- good for two hours at room temp, refrigerate after that
| - never freeze
27
Two components of urinalysis
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
28
How much blood does it take to make urine look bloody??
NOT very much
29
TNTC means what
Too numerous to count
30
What drug is commonly used in UTIs that renders UA useless?
Pyridium (Azo), orange color stains urine, have to wait about 24 hours to clear system before UA will work
31
What are the 10 tests on a UA dipstick
1. leukoctes
2. nitrite
3. urobilinogen
4. protein
5. pH
6. Blood
7. specific gravity
8. Ketone
9. bilirubin
10. glucose
32
Leukocytes on UA
- 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
33
What does it mean if 1+ UA esterase and 0 WBC in microscopic analysis?
NOT a UTI
34
Nitrites on UA
- 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
+ leukocytes and + nitrites on UA means likely have what
UTI (94% sensitive)
36
pH on urinalysis
- NL: 4.5 to 7.0
- <7 is acidic, many causes
- >7 is alkolotic, many causes
- mostly worthless per Dr. McNeill
37
What environment do E. coli prefer?
Alkaline or neutral pH. One way to help with UTIs is to create acidic urine. Citrus drinks like OJ or cranberry juice
38
Blood urinalysis
- 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
If a female pt has sx of UTI, 2-3+ UA blood, and is on menstrual period, can use UA to diagnose?
No… menstrual blood is possibly the cause of the positive UA blood… Either treat based on sx OR cath for clean blood
40
Specific gravity UA
- 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
Specific gravity UA
| Difference between osmolality and specific gravity
- 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
Specific gravity <1.010
- dilute urine
| - renal problems: kidney’s not able to concentrate urine like diabetes insipidus (lack ADH)
43
Specific gravity >1.020
- concentrated urine
- dehydration
- v/d
- DM
44
Glucose UA
- 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
What is common in UA for pregnant women
Spill glucose and protein
46
Ketones UA
- NL = negative
| - Seen in acidotic states
47
Metabolic states that cause ketones in UA
- DKA
- Pregnancy (eclampsia)
- Hyperthyroidism
- Fever
48
Dietary disorders that cause ketones in UA
- starvation/fasting
- vomiting/diarrhea
- high fat diet
- anorexia
49
Protein UA
- 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
What can cause false positive in protein UA
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
Microalbuminuria
- pathologic level
- what level leads to 1+ on dipstick, why important
- 30 to 300 mg/day pathologic
| - >30 is 1+ on dipstick, indication have pathology
52
What is considered normal renal function on a UA dipstick
- NL Cr
- Neg proteins (means kidney is filtering)
- NL specific gravity (means kidneys are concentrating appropriately)
53
Bilirubin on UA dipstick
- 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
Urobilinogen dipstick UA
- NL: 0.2 – 1.0
- Increased: hemolysis, hepatocellular dz
- Decreased: abx (no ability to create from conjugated bili), bile duct obstruction
55
What is urobilinogen
End product of conjugated bilirubin after it has passed through the bile ducts and metabolized in the intestines
56
Know the cycle of bilirubin
learned this in GI
57
Microscopic UA
| - list 10 items
- WBC (actual cells)
- RBC (actual cells)
- Casts and type
- crystals
- yeast
- epithelial cells and type
- trichomonas
- bacteria
- color
- clarity
58
How would blood in the urine be presented on microscopic UA?
- WBC: 8-13 or so
- RBC: TNTC
This is the normal composition
59
How would pus in the urine be presented on microscopic UA?
RBC and WBC are TNTC
60
Color in urine microscopy
- 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
Clarity in urine microscopy
NL = clear
| cloudy/turbid: abnormal particles (WBC, RBC, bacteria, mucus)
62
Epithelial cells in urine microscopy
- 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
Bacteria in urine microscopy
- 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
WBC in urine microscopy
- NL: 2-3
- Pyuria: >3
- indicates inflammation or infection
65
what is sterile pyuria?
- WBC without bacteria
| - indicates chronic urethritis, prostatitis, interstitial nephritis
66
RBC in urine microscopy
- NL: 2-5
- hematuria: >5
- commonly from menses
67
Non menses causes of hematuria
- RBCs from renal and GU system trauma
- UTI, tumor, stone, glomerulonephritis, pyelonephritis, smokers, exercise, polycystic kidneys
- dysmorphic RBC: suggests glomerular bleeding
68
Casts in urine microscopy
- cylindrical structures formed by intratubular precipitation of protein
- cells can be trapped within matrix of protein
69
List the 5 types of casts
- Hyaline
- RBC
- Leukocyte
- Fatty
- Waxy
70
What are the two casts that can be normal
- hyaline
| - waxy
71
Hyaline casts
- can be normal
- might indicate need for further w/u
- seen in concentrated urine, fever, exercise
72
RBC casts seen in what
glomerulonephritis
73
WBC casts seen in what
- 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
Fatty casts seen in what
- nephrotic syndrome (heavy proteinuria)
75
Crystals in urine microscopy - 5 types
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
What causes magnesium ammonium phosphate crystals in urine?
- proteus mirabilis
- infects kidneys, forms triple phosphate
- condenses and forms stone that fills entire renal pelvis and calyxes!
- "Staghorn calculus" or "struvite"
77
Table 7-19
Review
78
Hemolytic jaundice
- serum total bilirubin
- serum conjugated bilirbuin
- urine urobilinogen
- urine conj. bilirubin
- stool
- skin
- increased
- normal/slight elevation
- normal
- absent
- brown (nl)
- jaundice
79
biliary obstruction
- serum total bilirubin
- serum conjugated bilirbuin
- urine urobilinogen
- urine conj. bilirubin
- stool
- skin
- increased
- increased
- absent
- present
- clay-colored
- jaundice
80
Intrahepatic cell damage
- serum total bilirubin
- serum conjugated bilirbuin
- urine urobilinogen
- urine conj. bilirubin
- stool
- skin
- 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
Urine C and S
- > 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
