Updated: 10/6/2018

Acute Kidney Injury

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Snapshot
  • A 56-year-old man presents with lower abdominal pain. His symptoms have progressively worsened over the course of the day. Medical history is significant for benign prostatic hyperplasia on tamsulosin. His blood pressure is 144/106 mmHg (normally, his blood pressure is 120/80 mmHg). On physical examination he has bladder distension. Laboratory testing is significant for a creatinine of 2.4 mg/dL (last serum creatinine was 0.7 mg/dL.) (Post-renal acute kidney injury likely secondary to benign prostatic hyperplasia)
Introduction
  • Clinical definition
    • acute reduction in glomerular filtration rate (GFR)
      • recall that GFR represents the sum of the filtration rates of nephrons
        • therefore, GFR reflects functioning renal mass
  • Epidemiology
    • risk factors
      • hypertension
      • chronic kidney disease
      • dehydration and volume depletion
      • diabetes
      • chronic liver or lung disease
  • Etiology
    • prerenal causes
      • decreased renal perfusion (e.g., hemorrhage, congestive heart failure, and diuretic use)
    • intrarenal causes
      • acute tubular necrosis
        • ischemia and toxic causes
      • interstitial nephritis
      • glomerulonephritis
      • vasculitis
      • hemolytic uremic syndrome
    • postrenal causes
      • urinary flow obstruction (e.g., benign prostatic hyperplasia and nephrolithiasis)
  • Pathogenesis
    • based upcome etiology (look at etiology)
  • Prognosis
    • lower rates of recovery in patients > 65 years of age
    • increased risk of end-stage renal disease, chronic kidney disease, and mortality
Presentation
  • Symptoms
    • may be asymptomatic
    • oliguria
    • anuria
    • polyuria
    • confusion
  • Physical exam
    • hypertension
    • edema
    • decreased urine output
Imaging
  • Renal ultrasound
    • indication
      • initial imaging study for assessing acute kidney injury
        • can assess for renal size and hydronephrosis
        • to assess for postrenal obstruction
Studies
  • Labs
    • increase in serum creatinine by ≥ 0.3 mg/dL within 48 hours
    • blood urea nitrogen (BUN):creatinine ratio
    • urinalysis
      • dipstick
        • to assess for protein, glucose, leukocyte esterase, hemoglobin and myoglobin, and specific gravity
      • microscopy
        • for example
          • red dysmorphic cells suggests a glomerular etiology (e.g., glomerulonephritis)
          • muddy brown casts suggests tubular necrosis
          • white blood cell casts suggest pyelonephritis or acute interstitial nephritis
    • fractional excretion of Na+ (FeNa+)
      • if patient is on diuretics use FeUrea
    • urine osmolality and Na+
 
Studies To Assess For Prerenal, Intrarenal, and Postrenal Acute Kidney Injury (AKI)
Studies
Prerenal AKI  Intrarenal AKI
Postrenal AKI
Urine osmolality (mOsm/kg)
  • > 500
  • < 350
  • < 350
FeNa
  • < 1%
  • > 2%
  • < 1% in mild cases
  • > 2% in severe cases
Urine Na+ (mEq/L)
  • < 20
  • > 40
  • > 40
Serum BUN/Cr
  • > 20:1
  • < 15:1
  • Variable
 
Differential
  • Acute gastrointestinal bleeding
  • Rhabdomyolysis
  • Medication-induced impairment of creatinine secretion
    • cimetidine
    • trimethoprim
    • pyrimethamine
Treatment
  • Treatment is dependent on the etiology of AKI and its consequences
    • for example
      • a patient who is hyperkalemic and not responding to medical treatment should be dialyzed
      • a patient with a history of excessive fluid loss (e.g., diarrhea and vomiting) should be given intravenous fluid
Complications
  • Hyperkalemia
  • Metabolic acidosis
  • Uremic encephalopathy and platelet dysfunction
  • Anemia
  • Chronic kidney disease
 

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Questions (5)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.RL.27) A previously healthy 9-year-old, Caucasian girl presents to your office with severe abdominal pain. Her mother also mentions that she has been urinating significantly less lately. History from the mother reveals that the girl suffers from acne vulgaris, mild scoliosis, and had a bout of diarrhea 3 days ago after a family barbecue. Lab work is done and is notable for a platelet count of 97,000 with a normal PT and PTT. The young girl appears dehydrated, yet her serum electrolyte levels are normal. What is the most likely etiology of this girl's urinary symptoms? Review Topic

QID: 100981
1

Hypothalamic dysfucntion

8%

(1/13)

2

Surreptitious laxative use

8%

(1/13)

3

Toxic shock syndrome

0%

(0/13)

4

Shiga toxin production from Shigella

0%

(0/13)

5

Shiga-like toxin production from EHEC

85%

(11/13)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(M1.RL.71) A 49-year-old female with a history of alcoholism was found lying unconscious on a bench at a local park and rushed to the emergency department. Upon arrival, the patient regained consciousness and complained of intense bilateral flank pain and a recent decrease in urination. Urine microscopy demonstrated abundant square crystals of calcium oxalate that looked like “folded envelopes." Which of the following findings is most likely to be seen in this patient: Review Topic

QID: 101025
1

Metabolic alkalosis

21%

(3/14)

2

Anion gap metabolic acidosis

57%

(8/14)

3

Non-anion gap metabolic acidosis

14%

(2/14)

4

Respiratory acidosis

7%

(1/14)

5

Respiratory alkalosis

0%

(0/14)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
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