18 - Renal Function Test and Urinary Analysis Flashcards Preview

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Flashcards in 18 - Renal Function Test and Urinary Analysis Deck (53):
1

What are the tests you can do to assess renal function?

- Lab tests (BUN, creatinine, electrolytes - mainly K, but also Na and bicarb)
- Urinalysis (dip-stick, urine microscopy, electrolytes)
- Imaging studies (ultrasound, CT, functional studies)

2

Describe creatinine

- Byproduct of muscle creatine
- Nearly 100% FILTERED, minimally re-absorbed

3

What is the clinical utility of creatinine?

****

- Because of it’s filtration, reabsorption pattern, it is a useful marker of GFR
- Baseline values dependent on MUSCLE MASS
- Not a perfect test – inaccurate in mild impairment, no utility in CKD, individual variability******

EMPHASIZED that it is NOT a perfect test

4

Describe BUN

Marker of nitrogen/urea content of the blood

5

What does a rise in BUN mean?

***

Rise in BUN may indicate:
- Kidney injury/reduction in GFR
- Increased nitrogen load (UGI bleed, high-protein diet)
- Dehydration (less plasma = ↑ concentration)
- Steroid use

EMPHASIZED that if you eat a lot of meat and eggs, you can have high BUN

Need to exclude the other possibilities before you say there are kidney problems

6

What does low BUN mean?

- liver failure
- urea cycle defects

7

What is the clinical utility of BUN levels?

***

*Clinical Utility – used in conjunction with creatinine to assess renal function

**** Do NOT just look at one thing... Look at both of these ****

8

Describe what the BUN to Cr ratio tells you

STARRED SLIDE ******

Classically, this has been used to distinguish the origins of an acute kidney injury
- BUN:Cr > 20 suggests PRE-RENAL
- BUN:Cr

9

Describe testing electrolytes for kidney function

The kidney is responsible for maintaining electrolyte balance via filtration, reabsorption, and secretion

10

Describe potassium levels

Potassium – worry about increase, but low also a concern

11

Describe phosphorous levels

Phosphorus – elevation a concern in CKD

12

Describe sodium levels

Sodium – changes are related to disorders of WATER, not Na

13

Describe other electrolyte levels

- Bicarbonate – provides a clue in certain renal or endocrine causes for AKI
- Magnesium – check in hypokalemia
- Chloride – useful in confusing acid-base cases (calculating Anion Gap)
- Calcium – CKD, certain cases of AKI

14

Describe GFR estimation methods

Most common/easiest – serum creatinine
- Accuracy affected by mass, baseline, other factors
- Requires correction equations (MDR, Cockcroft-Gault)

More accurate options
- Inulin excretion – requires injection, monitoring
- 24h urine creatinine – difficult execution
- These are not very convenient

15

Describe a urinalysis


STARRED SLIDE ****

Clues on dip-stick
- Specific gravity – hydration status, renal concentrating capacity
- Proteinuria – mild, moderate, severe
* Test detects higher MW proteins (albumin)
- Infectious changes – leukocyte esterase, nitrites
- Blood – hematuria, rhabdomyolysis
* Test detects blood PROTEINS, not RBC’s
- Sugar, ketones - diabetes

***Normal UA = no blood, no nitrites, no ketones, no glucose, no leukocyte esterase***

16

What is on your list of differentials for hematuria

- IgA nephropathy
- Post-infectious nephropathy
- Hereditary nephropathy (Alports syndrome)
- Thin basement membrane disease
- Malignancy
- Nephrolithiasis
- Infection
- Foley trauma

17

Describe urine microscopy in the clinical setting

- Should ALWAYS be done when dip-stick is abnormal
- Normal microscopy – no “casts”, no RBC, no WBC, few or no epithelial cells

18

Describe abnormal findings on a urine microscopy

STARRED SLIDE ***

- WBC – infection, sterile pyuria
- Epithelial cells – may indicate sample contamination
- RBC – correlate with dip-stick blood
- Casts

19

Describe the abnormal finding of casts

STARRED SLIDE ***

Casts – cells coated with tubular proteins
- ***“Muddy brown” granular - Acute Tubular Necrosis
- Hyaline casts - Dehydration/volume depletion
- ***RBC – glomerulonephritis, vasculitis, renal infarct
- ***WBC – pyelonephritis, interstitial nephritis, post-strep GN
- Fatty, “maltese cross” – nephrotic syndrome
- Pigment – hemolysis, rhabdomyolysis, liver disease


Anytime you see "casts" it means that it has come from the tubules

This is important to make a good diagnosis, but no one can remember all of it, will need to reference later (?)

20

Describe the interpretation of a UA or micro

- Dip stick may indicate infection, heavy proteinuria or volume depletion
- Microscopy may help distinguish between different RENAL causes

21

What are the "pearls" of interpreting UA or micro?

STARRED SLIDE ****

- Muddy brown cast = ATN
- RBC cast = GN
- WBC cast = pyelo or AIN
- Eosinophils = AIN, contrast
- Dipstick blood pos, no RBC = Rhabdomyolysis
- ***No protein on dip, proteinuria on UPC ratio = Multiple myeloma (SSA can be added to turn dipstick pos)

22

What are the imaging studies we can use to look at the kidneys?

- CT
- Ultrasound

23

Describe the use of ultrasound

Cheap, easy, non-invasive, safe

You can see and diagnose...
- Bladder distension/urinary retention
- Hydronephrosis – distal obstruction
- Perinephric fluid collections – abscess, hematoma
- Kidney size –> atrophy = CKD
- Cysts – PCKD, tumors

24

Describe the use of CT

More expensive, radiation exposure, possible contrast exposure

Reasons to perform CT over ultrasound:
- To diagnose nephro- or urolithiasis
- Body habitus prevents quality ultrasound images
- Further delineation of lesions seen on ultrasound
- Angiography necessary

25

Describe AKI

(not emphasized)

Acute Kidney Injury
- Acute, rapid loss of renal function

26

What is the diagnostic criteria for AKI?

(not emphasized)

- Creatinine rise >=0.3mg/dL in =50% OR...
- UOP (urine osmotic pressure) =6hrs

27

Describe the severity of AKI

(not emphasized)

Occurs along a spectrum from mild injury to fulminant failure requiring dialysis (RRT=Renal Replacement Therapy)

28

How do you classify AKI?

STARRED SLIDE ***

3 categories based on the anatomic or functional location of the problem
- Pre-renal
- Post-renal
- Intra-renal

29

Describe case 1

42yo previously healthy male presents to the ED with confusion, lethargy, and fever over the past 3 days. He has also had nausea and vomiting for the past 24h. His family reports he has not had anything to eat or drink for the past 48h and is very weak.

PMH: HTN, hyperlipidemia

Medications: Lisinopril, Chlorthalidone,Simvastatin

No other significant social, surgical, or family history is reported.

30

Describe the physical exam for case 1

Physical:
- VS – 99.4, 122, 18, 105/60, 98% on RA
- Abdomen moderately tender, no peritoneal signs, hyperactive bowel sounds

31

Describe the labs for case 1

- BMP – Na-148, K-3.9, Cl-112, HCO3-26, BUN-48, Cr-1.9 (baseline 0.9). Glu-98
- UA – SpGr-1.03 (high), Protein, glucose, ketones, blood, leukocyte esterase, nitrites all NEG

32

What is the diagnosis for case 1?

Pre-renal AKI

33

Why is it pre-renal?

*** STARRED SLIDE***

- Caused by volume depletion and dehydration
- Also due to medications – diuretics, NSAID’s, ACEI/ARB
- Causes decreased hydrostatic pressure in the glomerulus

Other possible causes
- Heart failure
- Shock
- Renal artery stenosis

*****Most common cause of AKI in the ambulatory patient is pre-renal***** (this was the starred part)

34

Describe fractional excretion of Na

FeNa
- order urine Na & Cr
- then use serum Na & Cr from BMP

When faced with decreased perfusion the (healthy) kidney will CONSERVE sodium

35

When will FeNa be falsely elevated?

The FeNa will be falsely ELEVATED in patients on diuretics and those who have received IV saline (use FeUREA: Ubun instead of Una)

36

Give the percentages of FeNa that correlate with different diagnoses

2% = renal

37

What are the conclusions we can reach from case 1?

Other clues to pre-renal origin
- BUN:Cr ratio >20
- High specific gravity on UA – concentrated urine
- Mild hypernatremia – dehydration/vol deplete
- Otherwise normal UA – less likely to be intra-renal

Diagnosis?
- Pre-renal acute kidney injury due to volume depletion secondary to gastroenteritis

38

What is the treatment for pre-renal AKI?

- Volume replacement
- Hold diuretics, ACE/ARB’s, NSAID’s
- Avoid IV contrast dye if possible
- Correction of underlying pathology

39

Describe case 2

72yo M presents to the VA ED with complaints of fatigue, abdominal pain, and inability to urinate over the past 4 days.

PMH – HTN, CAD, COPD, DM II

Medications – carvedilol, lisinopril, amlodipine, lantus, aspirin, atorvastatin, and multiple inhalers

PSH – CABG x3, Appy, Lap chole, hernia x2

Social – Former smoker, no EtOH

***Pay attention to age***

40

Describe the physical exam in case 2

VS – 99.2, 88, 16, 160/102, 93% on RA

RRR, 2/6 SM RUSB, scattered wheezes

Lower abdomen tender, suprapubic fullness, a firm mass extends from the pelvis to umbilicus

41

Describe the labs in case 2

Na-141
K-4.2
Cl-108
HCO3-24
BUN-30
Cr-3.2 (baseline 1.1)***
Glu - 136

UA – SpGr 1.018. Trace blood. Otherwise neg

42

What else does the patient tell you?

Patient reports a 2-3 year history of progressive urinary frequency, 5-6x nightly nocturia

Digital rectal exam – 4+ enlarged, smooth, prostate. No masses or nodules.

FeNa – 1.4% (not on any diuretics)

43

What is the diagnosis for case 2?

Post-renal

44

Describe post-renal AKI

Obstruction of urine flow leading to increased pressure back through Bowman’s capsule

Clinically evident renal injury requires:
- Bilateral obstruction
- Obstruction distal/prior to reaching the bladder
- Unilateral obstruction of a solitary functioning kidney

45

What are some post-renal AKI causes?

*** ALL CAUSES RESULT IN... Increased hydrostatic pressure in Bowman’s capsule = decreased GFR

Intra-renal Obstruction myeloma cast nephropathy, renal tumors, large cysts

Abdominal Pathology – Tumors, compartment syndrome

Bladder Pathology– neurogenic bladder, tumors

Bladder Outlet Obstruction – ***BPH, urethral stricture, congenital malformations, kinked foley

Ureteral Obstruction – stones, scarring, congenital malformations

46

How do you diagnose post-renal AKI?

- FeNa not helpful – may be high, low, normal
- UA may be helpful (Hematuria – stones, tumors, urethral pathology)
- DRE – easy screen, may identify the most common cause (Enlarged prostate, Bladder Outlet Obstruction)
- Renal ultrasound (Bladder size, presence/absence hydronephrosis, masses, cysts)
- Other - bladder catheter insertion

47

What are the treatment options for post-renal AKI?

*** STARRED SLIDE ***

Relief of obstruction
- Foley catheter
- Ureteral stents for stones, strictures, tumors
- Surgery – abdominal tumors, compartment sy

Post-obstructive diuresis
- *** Phenomenon wherein an EXCESSIVE amount of urine output follows relief of obstruction
- *** Replace with IVF to match 50% of output
- Watch electrolytes

Know the two starred things ***

48

Give more information on case 2

- Renal ultrasound shows a distended bladder and bilateral hydronephrosis. No renal masses or cysts.
- Foley placed, 2000mL urine is obtained
- Patient is started on tamsulosin. His Cr returns to normal over the next 4 days. He is discharged with a foley catheter and urology follow-up (with future plans for voiding trial)

49

Describe acute hemodialysis

- One form of renal replacement therapy (RRT)
- Others: transplant and peritoneal dialysis

50

What is the purpose of hemodialysis?

Purpose: clear toxins and regulate volume

51

Describe continuous dialysis (CRRT)

Continuous dialysis (CRRT) for hypotension and increased intracranial pressure patients (ICU)

52

What are the indications for acute hemodialysis?

***** NEED TO KNOW *****

***STARRED SLIDE***

***** NEED TO KNOW *****
- A: uncorrectable acidosis
- E: electrolyte (hyperkalemia) resistant to treatment
- I: intoxication (meds)
- O: overload (volume, pulmonary edema)
- U: uremia

KNOW THIS WORD FOR WORD - TEST QUESTION ***

53

What should you focus on?

- LM, IF, EM (first lecture)
- Characteristics of each disease (first lecture)
- UA - casts and other things labeled with a star ***