link
Bookmarks
Introduction to Renal Physiology and Contrast
Alessandro Furlan, MD; Ghaneh Fananapazir, MD, FSAR, FSRU, FSABI
To access 4,300 diagnoses written by the world's leading experts in radiology.Try it free - 15 days

Principles of Renal Physiology

  • The main functions of the kidneys are the maintenance of homeostasis, removal of metabolic waste products, and production of urine. The nephron is the functional unit of the kidney. Its functions are carried out with a combination of glomerular filtration, tubular reabsorption, and tubular secretion. Filtration is conducted in the renal corpuscle (glomerulus, Bowman capsule) in the cortex, while reabsorption and secretion occur in the different tubular components (proximal, distal convoluted tubule, loop of Henle, and collecting ducts) located in the cortex and medulla.
  • Glomerular filtration rate (GFR) is the volume of fluid filtered in the glomerulus per unit of time. It is determined by the net filtration rate, capillary permeability, and surface area of the capillary bed. The normal GFR in adults is 125 mL/minute.

Iodinated Contrast Media

  • Iodinated contrast media (ICM) are hydrophilic chemical compounds excreted from the kidneys by glomerular filtration alone. Enhancement (i.e., increased attenuation) after injection of ICM is based on several agent-related (e.g., concentration, volume, rate of injection), patient-related (weight, height, cardiac output), and technical-related (scan delay for CT acquisition) factors. ICM are described based on their dissociation in solution (ionic, nonionic), osmolarity compared to plasma (high-, iso-, low osmolar), and number of triiodinated benzene groups (monomer, dimer).
  • Types of Contrast Media
  • Contrast-induced nephropathy (CIN) is an acute kidney injury (absolute increase in serum creatinine of 0.5 mg/dL or relative 25% increase from baseline value) occurring within 24-48 hours following intravascular administration of contrast material. The most important risk factor for CIN is underlying renal dysfunction (GFR < 60 mL/min/1.73m²). The American College of Radiology recommends obtaining a baseline creatinine in all patients with suspected renal dysfunction. Other risk factors include decreased renal perfusion (e.g., heart failure), age > 70 years, diabetes mellitus, concomitant use of nephrotoxic drugs (e.g., NSAIDs), multiple myeloma, large volume of contrast media, and high-osmolar contrast media. In patients at risk for CIN but still requiring injection of contrast media, the following prophylactic measures should be taken: Intravenous hydration, lower dose of hypo- or iso-osmolar contrast media, and no nephrotoxic drugs.

MR Contrast Media

  • Gadolinium-based MR contrast agents (GBCA) are paramagnetic compounds that increase signal intensity (i.e., enhancement) by increasing the T1 relaxation rate. The evaluation of the genitourinary tract is conducted using extracellular agents, preferably with high relaxivity.
  • Gadolinium agents are divided into 3 groups depending on their structure and excretion. Group I agents are linear compounds and are rarely used and are largely excreted by the kidneys. Group II agents are macrocyclic compounds and are the most commonly used agents and are largely excreted by the kidneys. The group III agent (gadoxetate disodium) is linear but has a significant (50%) hepatobiliary excretion and is marketed for liver lesion characterization and detection.
  • Nephrogenic systemic fibrosis (NSF) is a systemic fibrosing disorder occurring in patients with renal dysfunction. An association with exposure to GBCA is accepted although the exact mechanism remains unknown. The disease has been reported weeks to months after contrast injection, and no effective treatment is available. The major risk factors are renal dysfunction, type of GBCA, and cumulative dose of contrast. NSF has been almost exclusively seen in association with group I agents. As group I agents are now rarely used, the incidence of NSF has decreased. The risk of withholding a group II agent usually outweighs the very low risk of NSF in patients with acute kidney injury or low renal function.

Adverse Reactions to Contrast Media

  • Adverse reactions to contrast media can be classified as allergic-like and physiologic and have an overall low incidence rate. The most significant risk factor for an allergic-like reaction is a documented allergic reaction to prior exposure. The majority of the reactions can be classified as mild and are non-life-threatening (e.g., limited urticaria, nausea/vomiting). Moderate (e.g., facial edema, vasovagal reaction) and severe (e.g., laryngeal edema with hypoxia, hypertensive emergency) adverse reactions need to be recognized and managed promptly. For prophylaxis measures and management of adverse reactions to contrast media, consult the most recent guidelines from the ACR.

Selected References

  1. Weinreb JC et al: Use of intravenous gadolinium-based contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 298(1):28-35, 2021
  2. Rudnick MR et al: The controversy of contrast-induced nephropathy with intravenous contrast: what is the risk? Am J Kidney Dis. 75(1):105-13, 2020
  3. Woolen SA et al: Risk of nephrogenic systemic fibrosis in patients with stage 4 or 5 chronic kidney disease receiving a group II gadolinium-based contrast agent: a systematic review and meta-analysis. JAMA Intern Med. 180(2):223-30, 2020
  4. Ellis JH et al: Influence of clinical factors on risk of contrast-induced nephrotoxicity from IV iodinated low-osmolality contrast material in patients with a low estimated glomerular filtration rate. AJR Am J Roentgenol. 213(5):W188-93, 2019
  5. Luk L et al: Intravenous contrast-induced nephropathy-The rise and fall of a threatening idea. Adv Chronic Kidney Dis. 24(3):169-75, 2017
  6. McDonald RJ et al: Controversies in contrast material-induced acute kidney injury: closing in on the truth? Radiology. 277(3):627-32, 2015
  7. Davenport MS et al: Contrast material-induced nephrotoxicity and intravenous low-osmolality iodinated contrast material. Radiology. 267(1):94-105, 2013
  8. McDonald JS et al: Frequency of acute kidney injury following intravenous contrast medium administration: a systematic review and meta-analysis. Radiology. 267(1):119-28, 2013
  9. McDonald RJ et al: Intravenous contrast material-induced nephropathy: causal or coincident phenomenon? Radiology. 267(1):106-18, 2013
Related Anatomy
Loading...
Related Differential Diagnoses
Loading...
References
Tables

Tables

Principles of Renal Physiology

  • The main functions of the kidneys are the maintenance of homeostasis, removal of metabolic waste products, and production of urine. The nephron is the functional unit of the kidney. Its functions are carried out with a combination of glomerular filtration, tubular reabsorption, and tubular secretion. Filtration is conducted in the renal corpuscle (glomerulus, Bowman capsule) in the cortex, while reabsorption and secretion occur in the different tubular components (proximal, distal convoluted tubule, loop of Henle, and collecting ducts) located in the cortex and medulla.
  • Glomerular filtration rate (GFR) is the volume of fluid filtered in the glomerulus per unit of time. It is determined by the net filtration rate, capillary permeability, and surface area of the capillary bed. The normal GFR in adults is 125 mL/minute.

Iodinated Contrast Media

  • Iodinated contrast media (ICM) are hydrophilic chemical compounds excreted from the kidneys by glomerular filtration alone. Enhancement (i.e., increased attenuation) after injection of ICM is based on several agent-related (e.g., concentration, volume, rate of injection), patient-related (weight, height, cardiac output), and technical-related (scan delay for CT acquisition) factors. ICM are described based on their dissociation in solution (ionic, nonionic), osmolarity compared to plasma (high-, iso-, low osmolar), and number of triiodinated benzene groups (monomer, dimer).
  • Types of Contrast Media
  • Contrast-induced nephropathy (CIN) is an acute kidney injury (absolute increase in serum creatinine of 0.5 mg/dL or relative 25% increase from baseline value) occurring within 24-48 hours following intravascular administration of contrast material. The most important risk factor for CIN is underlying renal dysfunction (GFR < 60 mL/min/1.73m²). The American College of Radiology recommends obtaining a baseline creatinine in all patients with suspected renal dysfunction. Other risk factors include decreased renal perfusion (e.g., heart failure), age > 70 years, diabetes mellitus, concomitant use of nephrotoxic drugs (e.g., NSAIDs), multiple myeloma, large volume of contrast media, and high-osmolar contrast media. In patients at risk for CIN but still requiring injection of contrast media, the following prophylactic measures should be taken: Intravenous hydration, lower dose of hypo- or iso-osmolar contrast media, and no nephrotoxic drugs.

MR Contrast Media

  • Gadolinium-based MR contrast agents (GBCA) are paramagnetic compounds that increase signal intensity (i.e., enhancement) by increasing the T1 relaxation rate. The evaluation of the genitourinary tract is conducted using extracellular agents, preferably with high relaxivity.
  • Gadolinium agents are divided into 3 groups depending on their structure and excretion. Group I agents are linear compounds and are rarely used and are largely excreted by the kidneys. Group II agents are macrocyclic compounds and are the most commonly used agents and are largely excreted by the kidneys. The group III agent (gadoxetate disodium) is linear but has a significant (50%) hepatobiliary excretion and is marketed for liver lesion characterization and detection.
  • Nephrogenic systemic fibrosis (NSF) is a systemic fibrosing disorder occurring in patients with renal dysfunction. An association with exposure to GBCA is accepted although the exact mechanism remains unknown. The disease has been reported weeks to months after contrast injection, and no effective treatment is available. The major risk factors are renal dysfunction, type of GBCA, and cumulative dose of contrast. NSF has been almost exclusively seen in association with group I agents. As group I agents are now rarely used, the incidence of NSF has decreased. The risk of withholding a group II agent usually outweighs the very low risk of NSF in patients with acute kidney injury or low renal function.

Adverse Reactions to Contrast Media

  • Adverse reactions to contrast media can be classified as allergic-like and physiologic and have an overall low incidence rate. The most significant risk factor for an allergic-like reaction is a documented allergic reaction to prior exposure. The majority of the reactions can be classified as mild and are non-life-threatening (e.g., limited urticaria, nausea/vomiting). Moderate (e.g., facial edema, vasovagal reaction) and severe (e.g., laryngeal edema with hypoxia, hypertensive emergency) adverse reactions need to be recognized and managed promptly. For prophylaxis measures and management of adverse reactions to contrast media, consult the most recent guidelines from the ACR.

Selected References

  1. Weinreb JC et al: Use of intravenous gadolinium-based contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 298(1):28-35, 2021
  2. Rudnick MR et al: The controversy of contrast-induced nephropathy with intravenous contrast: what is the risk? Am J Kidney Dis. 75(1):105-13, 2020
  3. Woolen SA et al: Risk of nephrogenic systemic fibrosis in patients with stage 4 or 5 chronic kidney disease receiving a group II gadolinium-based contrast agent: a systematic review and meta-analysis. JAMA Intern Med. 180(2):223-30, 2020
  4. Ellis JH et al: Influence of clinical factors on risk of contrast-induced nephrotoxicity from IV iodinated low-osmolality contrast material in patients with a low estimated glomerular filtration rate. AJR Am J Roentgenol. 213(5):W188-93, 2019
  5. Luk L et al: Intravenous contrast-induced nephropathy-The rise and fall of a threatening idea. Adv Chronic Kidney Dis. 24(3):169-75, 2017
  6. McDonald RJ et al: Controversies in contrast material-induced acute kidney injury: closing in on the truth? Radiology. 277(3):627-32, 2015
  7. Davenport MS et al: Contrast material-induced nephrotoxicity and intravenous low-osmolality iodinated contrast material. Radiology. 267(1):94-105, 2013
  8. McDonald JS et al: Frequency of acute kidney injury following intravenous contrast medium administration: a systematic review and meta-analysis. Radiology. 267(1):119-28, 2013
  9. McDonald RJ et al: Intravenous contrast material-induced nephropathy: causal or coincident phenomenon? Radiology. 267(1):106-18, 2013