What are the Three Types of AKI?

Understanding AKI: Types, Causes & Warning Signs

Acute kidney injury (AKI) is a sudden deterioration of kidney function, occurring over hours to days, leading to toxin accumulation and fluid/electrolyte imbalances. This complex condition consists of various aetiologies. Understanding classifications of AKI can help plan a treatment strategy and improve patient health.

Classification: Three Types of AKI  

AKI happens when the kidneys suddenly restrict or totally stop functioning, such as stopping filtering waste from the blood. This condition results in toxin accumulation and an imbalance of electrolytes that disrupt the body's capability of regulating fluids. The rapid deterioration of the kidneys can develop within a few days or a few hours.  

AKI has three types, and here are the brief descriptions:

1. Prerenal AKI: Prerenal acute kidney injury happens due to inadequate blood supply to the kidney, resulting in decreased glomerular filtration rate. This is the most commonly affected AKI with a high risk of renal damage.  
2. Intrinsic AKI: Intrinsic AKI is the condition of direct impairment or damage to the kidney tissues.  It damages the nephron, which filters waste from the blood.  
3. Postrenal AKI: It is the result of obstruction or blockage in the urinary tract that hampers urine flow from the kidney to the bladder. This obstruction from the renal pelvis to the urethra restricts kidney function by preventing urine.

Primary Causes of Prerenal Acute Kidney Injury

Prerenal AKI has various causes, including:

• Reduced blood pressure
• Excessive bleeding
• Heart diseases like heart attacks or heart failure
• Diarrhoea
• Liver failure
• Infections
• Prolonged use of non-steroidal anti-inflammatory drugs like ibuprofen, aspirin, and naproxen
• Anaphylaxis
• Dehydration
   

Key Causes of the Intrinsic AKI

Apart from problems with connective tissues and blood vessels, there are many causes for intrinsic AKI, including:

• Clots or injury in blood vessels
• Inflammation in the structural units of the kidneys
• Impact of autoimmune diseases like vasculitis and lupus
• Cancer
• Kidney infection
• Using medications with antibiotics, proton pump inhibitors and NSAIDs
• Alcohol consumption
• Blood disorders such as thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome.
   

Causes of the Postrenal AKI

This type of AKI has some potential causes, such as:

• Bladder or kidney tumours
• Kidney stones
• Cancer in the urinary bladder, cervix or colon
• Blood clotting in the urinary tract
• Effect of prostate disease, including prostate cancer and prostatic hyperplasia
• Damage to bladder function
• Nerve system issues that control the urine flow
   

Symptoms of AKI  

Acute kidney injury symptoms appear over days or a period. Common signs include:

• Swelling in ankles, feet and legs due to fluid retention (oedema)
• Decreased urinary frequency
• Fatigue
• Severe pain in the back or abdomen
• Chest pain
• Muscle cramps
• Seizures
• Blood in urine
• Breathing issues
• Dark-coloured urine
   

Prerenal, intrinsic and postrenal are the three types of acute kidney injury. Prerenal KRI occurs due to reduced blood flow in the kidney, dehydration, liver failure and heart failure.

Conversely, intrinsics cause direct kidney damage and happen due to prolonged medication with nephrotoxic drugs and inflammation of the filtering units of the kidneys. Postrenal AKI occurs due to prostate enlargement, kidney stones and tumours.