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Medicine Clerkship > Learning Objectives - Acute Renal Failure and Renal Tests > Flashcards

Learning Objectives - Acute Renal Failure and Renal Tests Flashcards

1
Q

What does the specific gravity measure?

A

Weight of dissolved particles in the urine compared with distilled water (1.001-1.035)

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2
Q

What does the urine osmolality measure?

A

Number of particles dissolved in urine (40-1400)

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3
Q

Define acute kidney injury.

A

An abrupt (within 48 hours) decrease in glomerular filtration function with a concomitant elevation in serum creatinine

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4
Q

What are 4 signs of hypovolemia? Which are the best predictors?

A
  1. Orthostatic hypotension
  2. Sunken eyes/dry axilla (best predictors)
  3. Dry mucous membranes (sensitive, can help rule out if absent)
  4. Skin tenting (poor skin turgor)
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5
Q

What is the most common cause of decreased renal function in hospitalized patients and the most common cause of renal failure?

A

Decreased renal perfusion

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6
Q

What is the pathophysiology of pre-renal dysfunction?

A

Decreased renal perfusion due to hypovolemia or hypotension compromises renal function. Tubules enhance absorption of sodium and water; this also causes increased passive reabsorption of urea

Tubular and glomerular function are intact

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7
Q

List 4 causes of decreased renal perfusion.

A
  1. Hypovolemia (vomiting, diarrhea, poor PO intake, diuretics, fever, surgical fluid losses, burns, hemorrhage)
  2. Decreased CO (CHF, MI, etc.)
  3. Systemic vasodilation (sepsis, cirrhosis, anesthesia, etc.)
  4. Renal hypoperfusion (medications vasoconstricting afferent arterioles, atherosclerosis, fibromuscular dysplasia)
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8
Q

Orthostasis implies a loss of ___% of intravascular volume. Supine hypotension and tachycardia in the absence of fever or infection suggests ___% loss of intravascular volume.

A

20; 40

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9
Q

Expected UA findings in pre-renal AKI?

A
  1. Spec grav >1.020
  2. BUN/Cr ratio >20
  3. FENa <1%
  4. UOsm >350 (normal)
  5. UNa <20
  6. UCr/PCr >40
  7. Hyaline casts
    ~UA can be normal
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10
Q

DDx - elevated BUN/Cr ratio

A

Pre-renal AKI
Catabolic state (sepsis, steroid therapy)
GI bleeding
High protein intake (diet, TPN)
Tetracycline
Decreased excretion (obstruction, pre-renal)

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11
Q

What are the top three causes of intrinsic renal AKI in hospitalized patients?

A
  1. ATN 2/2 sepsis
  2. Post-operative renal ischemia
  3. Contrast nephropathy
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12
Q

DDx - intrinsic renal AKI

A
  1. Vascular lesions (renal artery occlusion, vasculitis, TTP, HUS) - rare
  2. Glomerular lesions (Goodpasture’s, Wegener’s, PSGN, lupus) - 5%
  3. Interstitial nephritis (allergic interstitial nephritis 2/2 hypersensitivity, infection, AI disease) - 10%
  4. Intra-tubule deposition/obstruction
  5. ATN - 85%
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13
Q

What drugs commonly cause interstitial nephritis?

A

FQs, sulfas, beta lactams, NSAIDs, hydrochlorothiazde (rare)

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14
Q

List # causes of ATN

A
  1. Ischemia (pre-renal azotemia, microvascular coagulation problem, HUS, snake bite, obstetrical complications)
  2. Nephrotoxins (AGs, radiocontrast, myoglobin, hemoglobin, chemo, myeloma light chains, etc.)
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15
Q

Expected UA findings in intrinsic renal AKI?

A
  1. Specific gravity 1.010
  2. BUN/Cr ratio <20
  3. FENa >2%
  4. UOsm 250-300 (or less)
  5. UNa >40
  6. UCr/PCr <20
  7. Various casts
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16
Q

What historical finding is highly suggestive of acute renal obstruction?

A

Complete anuria (note that this can be seen with severe dehydration and aortic dissection through both renal arteries)

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17
Q

Define oliguria and anuria.

A

Oliguria <400 mL/day

Anuria <50 mL/day

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18
Q

Expected UA findings in post-renal AKI?

A

Typically normal unless there is a complete obstruction; may see RBCs/WBCs

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19
Q

DDx - acute renal obstruction in the renal tubules?

A
  1. Crystals (uric acid)
  2. Acyclovir
  3. Indinavir
  4. Sulfa drugs
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20
Q

DDx - acute renal obstruction in the ureters?

A
  1. Tumors
  2. Calculi
  3. Clot
  4. Sloughed papillae
  5. Retroperitoneal fibrosis
  6. Lymphadenopathy
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21
Q

DDx - acute renal obstruction in the bladder neck?

A
  1. Tumors
  2. Calculi
  3. BPH
  4. Prostate/cervical cancer
  5. Neurogenic bladder
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22
Q

DDx - acute renal obstruction in the urethra?

A
  1. Stricture
  2. Tumors
  3. Obstructed indwelling catheters
  4. Posterior urethral valve (young male)
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23
Q

Describe the metabolic consequences of significant reductions in renal function.

A
  1. Hyperkalemia (decreased excretion of potassium)
  2. Hyperphosphatemia (decreased excretion of phosphate)
  3. Hyperuricemia
  4. Hypocalcemia (decreased ability to form active Vitamin D)
  5. Metabolic acidosis (decreased H+ excretion, also causes K+ to move extracellularly, furthering the hyperK)
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24
Q

What are the 5 major indications for dialysis?

A
  1. Acidosis (in a patient that is volume overloaded, unable to respond to diuretics/bicarb therapy/other supportive measures)
  2. Electrolyte derangements (that do not respond to supportive measures)
  3. Ingestion of toxins/medications that are water soluble and can be removed easily via dialysis
  4. Overload of volume (does not respond to diuretics or causes CP collapse)
  5. Uremia
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25
Q

What is the most common indication for dialysis?

A

Hyperkalemia

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26
Q

Presenting signs and symptoms of uremia?

A

Fatigue, anorexia, dysgeusia, cramps, N/V, sleep disturbances, amenorrhea, sexual dysfunction, itching, hiccups, confusion, lethargy, inability to concentrate, peripheral neuropathy, seizures, asterixis, pericarditis

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27
Q

Calculate FENa?

A

FENa = (UNa x PCr)/(PNa x UCr)

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28
Q

What are major risk factors for contrast-induced nephropathy?

A
  1. CKD (Cr>1.5, GFR <60)
  2. Age (>75)
  3. Hypovolemia
  4. DM, CHF, Cirrhosis/nephrosis, PVD
  5. NSAID use
  6. High-dose contrast or repeated procedures over a 72-hour period
  7. Intra-raterial injection
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29
Q

Prevention of contrast-induced nephropathy?

A
  1. Identify at-risk patients
  2. Avoid high osmolar radiocontrast agents
  3. D/C NSAIDs
  4. Give IV hydration with NS or isotonic NaHCO3
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30
Q

True or false - serum creatinine is a relatively late biomarker of acute injury

A

True

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31
Q

List 6 medications that can induce renal dysfunction through vasoconstriction of the afferent arteriole of the kidney.

A
  1. Amphotericin B
  2. Cyclosporine-A
  3. NSAIDs
  4. Radiocontrast
  5. Tacrolimus
  6. Aspirin (not typically seen at standard doses)
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32
Q

___ vasodilate the afferent arteriole, causing a decrease in filtration pressure.

A

ARBs (valsartan)

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33
Q

The presence of both acute stroke and AKI could suggest what?

A

TTP (thrombotic thrombocytopenic purpura), a microvacular endotheliopathy that leads to intravascular hemolysis and microthrombosis

34
Q

Classic pentad of clinical features of TTP?

A 
Microangiopathic hemolytic anemia*
Thrombocytopenia*
Renal failure
Fever
CNS problems (acute stroke, AMS, etc.)
*Required for diagnosis
35
Q

Cause of AKI associated with livedo reticularis, low serum complement levels, eosinophilia, s/p invasive angiographic procedure (2-3 weeks)?

A

Cholesterol embolization, showering of cholesterol crystals in the kidney

36
Q

Discuss metformin and its effect on the kidneys.

A

Metformin is excreted 100% unmetabolized by the kidneys. It is no nephrotoxic, but can lead to lactic acidosis in patients with renal failure or liver disease

37
Q

Work-up of the etiology of renal failure?

A
  1. Blood glucose (DKA)
  2. CK/urine myoglobin (rhabdomyolysis)
  3. UA (ketonuria/ketoacidosis)
  4. Osmolar gap calcuation
  5. CBC (WBC count - sepsis)
  6. Lactate level (lactic acidosis)
  7. Post-void residual
  8. Renal U/S (obstruction, pre-exiting renal disease)
  9. Spot urine/creatinine ratio (underlying glomerular injury)
  10. Urine chemistries (calculate FENa)
38
Q

Calculate serum osmolality?

A

Serum sodium + glucose/18 + BUN/2.8

39
Q

When is an osmolar gap calculated?

A

Toxic alcohol ingestions

40
Q

Interpret the results of a post-void residual.

A

> 100 mL - obstruction from the bladder neck or lower

<100 mL - does not exclude obstruction higher up

41
Q

Normal kidney size vs. small/atrophic kidneys w/increased echogenicity vs. enlarged vs. asymmetric kidney size?

A

Normal - acute process
Small/atrophic - chronic kidney disease
Enlarged - diabetic nephropathy
Asymmetric - renovascular disease

(Can be falsely negative in early obstruction, severe dehydration, retroperitoneal fibrosis)

42
Q

When can the FENa not be used? What is used in its place?

A

Patients on diuretics, patients with pre-existing CKD

Calculate FEUrea

43
Q

Management/treatment of AKI?

A
  1. Identify and correct pre-renal and post-renal conditions
  2. Volume management - IV fluids (if depleted), diuretics (if overloaded), daily weights, strict I/O
  3. Renal diet (low K+, phosphate, protein)
  4. Stop NSAIDs and other nephrotoxic agents, avoid nephrotoxic ABX (AG, amphotericin), avoid radiocontrast. Renal dosing.
  5. Monitor electrolytes (hyperK, hyperPH), AG, acid-base
  6. Identify and aggressively treat infections (minimize indwelling lines, remove Foley if anuric)
  7. Identify and treat bleeding tendency, GI prophylaxis, avoid aspirin, transfuse PRN
  8. Indications for
44
Q

Compare glomerular and non-glomerular hematuria.

A

Glomerular: red cell casts, dysmorphic red cells of varying sizes and shapes, dipstick + for protein

Non-glomerular: red cells look the same, dipstick NEGATIVE for protein

  • Symptomatic: infection (pyelo), nephrolithiasis, etc.
  • Asymptomatic: urothelial malignancy or cancer
45
Q

What is the RIFLE criteria?

A

Risk (stage 1, 1.5x Cr, GFR decreases by 25%)
Injury (stage 2, 2x Cr, GFR decreases by 50%)
Failure (stage 3, 3x Cr OR acute risk of 0.5 OR >4.0, GFR decreases by 75%)
Loss of function for >4 weeks
ESRD - complete loss of function for >3 months

46
Q

DDx - elevated specific gravity (>1.010)

A 
Concentrated urine
Glucose, protein, dextrans, radiographic contrast
Dehydration
SIADH
Adrenal insufficiency
Pre-renal azotemia
47
Q

RBC casts indicate what?

A

Nephritic process/glomerular disease

48
Q

WBC casts indicate what?

A

Infection or inflammation, most common in interstitial nephritis or pyelonephritis

49
Q

Granular casts?

A

Aka “muddy brown casts”

Specific for ATN

50
Q

Hyaline casts?

A

Pre-renal failure, also healthy people, people on diuretics

51
Q

1+ (~30 mg/dL) proteinuria may occur in what settings?

A

Heat stress, acute illness, fever, exercise, high venous pressure

52
Q

What are the three categories of persistent proteinuria?

A
  1. Overflow (capacity to reabsorb normally filtered protein in proximal tubules is overwhelmed due to overproduction/Hgb/Mgb-uria
  2. Tubular (decreased reabsorption of filtered proteins by tubules due to damage, usually <2 g)
  3. Glomerular (microalbuminuria to overt proteinuria, usually >3.5g)
53
Q

Expected 24 hour protein in the following situations:

  1. Renal disease
  2. Pregnancy
  3. Glomerular disease
  4. Microalbuminuria
A
  1. 150-300 mg/24 hrs
  2. 300 mg/24 hrs
  3. > 3.5 g
  4. > 30 mg/24 hrs
54
Q

Lipid body/fatty casts?

A

Nephrotic syndrome

55
Q

Normal Pr:Cr ratio?

A

<0.15

56
Q

Possible physical exam findings in CKD?

A

Vitals - HTN
HEENT - fundoscopic findings of chronic HTN/DM
CV - elevated JVP, irregular rhythm (arrhythmia 2/2 electrolyte disorder), pericardial friction rub (uremia)
Resp - crackles (volume overload)
GI - palpable kidneys (PCKD), abdominal bruits (renal artery stenosis)
Neuro - AMS, peripheral neuropathy, asterixis, seizures
Skin - pallor (anemia), dry, uremic frost, rash (vasculitis, SLE)
Ext - edema, arthritis (SLE)

57
Q

Define CKD.

A

Presence of markers of kidney damage for >3 months which may include structural or functional abnormalities with or without a decrease in GFR

58
Q

Common pre-renal causes of CKD?

A

Renal hypoperfusion (renal artery stenosis 2/2 atherosclerotic disease or fibromuscular dysplasia)

59
Q

Common intrinsic renal causes of CKD?

A

Diabetic nephropathy (most common cause)
HTN
Glomerulonephritis
PCKD (Autosomal dominant)
Long-term analgesic use (acetaminophen, ibuprofen)
Rare systemic diseases (amyloidosis, vasculitis - GPA, multiple myeloma)
AI diseases (SLE)

60
Q

Most common cause of post-renal CKD?

A

BPH

61
Q

What is GFR?

A

Amount of blood per unit time cleared of some substance (mL/min)

62
Q

In order for the clearance of a substrate to equate with GFR, the substance must have what 3 properties?

A
  1. Smaller than 60 kD (~size of albumin)
  2. Freely filterable/water soluble
  3. Not reabsorbed or secreted
63
Q

Why does creatinine clearance overestimate GFR if GFR is low?

A

Increased secretion from the vasa recta into the Loop of Henle

64
Q

List 5 factors affecting endogenous creatinine production.

A
  1. Age
  2. Sex
  3. Race
  4. Muscle mass
  5. Renal disease
65
Q

Calculate creatinine clearance (mL/min) using Cockroft-Gault?

A

[(140-age) x ideal weight (kg)] / Serum creatinine (mg/dL) x 72

Multiple total by 0.85 if female

66
Q

Calculate creatinine clearance with a 24 hour urine study?

A

Urine volume (mL) x Urine creatinine concentration / Serum creatinine x time in minutes

67
Q

Normal GFR? Correction for age?

A

Females: 100 mL/min/1.73 M2
Males: 120 mL/min/1.73 m2

After age 40, lost ~1 mL/min/year

68
Q

What is creatinine?

A

Metabolite of creatine, which is a phosphate bus produced by the liver that lives in muscles to help convert ATP to ADP and back

69
Q

Who will have low serum creatinine with normal kidney function?

A

Elderly (no muscle mass, not active)
Liver disease (no muscle mass, not producing creatine)
Malnutrition

70
Q

Who will have higher serum creatinine with normal kidney function?

A

High muscle mass/physically active

71
Q

What is cystatin C?

A

Protein encoded by the CST3 gene and used as a biomarker of kidney function, less influenced by liver disease, nutrition status, but can be influenced by cell turnover

72
Q

Microalbuminuria vs. macroalbuminuria?

A

Micro - <300 mg/day, not dipstick positive

Macro - >300 mg/day, dipstick positive

73
Q

Stages of kidney disease by GFR?

A 
1 - normal GFR with proteinuria or urine sediment changes
2 - 60-90
3 - 30-59
4 - 15-29
5 - <15
74
Q

Work-up for CKD?

A
  1. CBC (anemia)
  2. Iron-studies (iron deficiency frequently present)
  3. Fasting lipid panel (CV disease prevention)
  4. PTH (r/o secondary hyperPTH)
  5. Spot urine for albumin and creatinine
  6. EKG (electrolytes)
  7. Renal U/S
75
Q

What is the most common cause of death in CKD?

A

CV disease

76
Q

Which patients with CKD are considered to be at increased CV risk?

A

Patients 50+ years with CKD (eGFR<60), recommend statins

77
Q

Waxy casts?

A

Advanced renal failure/CKD

78
Q

Urinary eosinophils?

A

AIN

79
Q

Normal #WBCs in urine?

A

2-5 WBCs/hpf or less

80
Q

Dx - decreased specific gravity?

A 
Excessive hydration (nephrogenic DI)
Unable to concentrate urine (acute GN, pyelonephritis, ATN)
81
Q

In patients with CKD and proteinuria, what are first line medications and why? Major side effect?

A

ACEIs and ARBs

Often will require more than 1 antihypertensive to reach BP goal - diuretics (loop better than HCTZ in stage 4/5)

Lessen extent of proteinuria, slow progression of CKD

Hyperkalemia

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