Introduction

Acute kidney injury refers to loss of kidney function, usually within a few days. Here, we talk about the causes and symptoms of acute kidney injury, as well as the various diagnostic and treatment solutions that may be deployed.

Pharmacists are expected to have a rounded knowledge of disease states that impact the kidney and how best these conditions should be treated. The NAPLEX exam and other pharmacy board exams test your knowledge of acute kidney injury.

Here, we review the fundamental clinical detail that you are expected to know.

Let’s get started.

What is Acute Kidney Injury?

When the kidney is suddenly unable to properly filter blood, this invariably leads to accumulation of waste products. This can prove hazardous. For example, it impairs the kidney’s ability to adequately maintain electrolyte and fluid balance.

As the name suggests, acute kidney injury develops rapidly – typically within a few days but may develop over the course of one week.

Acute kidney injury generally requires hospitalization. Most cases develop in patients with pre-existing disease who have already been hospitalized for a different complaint.

Symptoms of Acute Kidney Injury

Symptoms of AKI vary, but may involve any of the following:

• Fluid retention – leading to lower extremity swelling
• Reduced urine output
• Dyspnea
• Fatigue
• Weakness
• Chest pain
• Nausea

In some cases, no symptoms present and acute kidney injury is detected from other laboratory test results.

Causes of Acute Kidney Injury

There are three classes used to differentiate the causes of acute kidney injury:

• Prerenal
• Intrinsic
• Postrenal

Let’s review each of these causes in turn.

Prerenal acute kidney injury refers to causes that impact blood flow to the kidney or cause a reduction in glomerular filtration rate (GFR).

Examples include:

• Low blood volume
• Dehydration
• Heart failure
• Organ failure
• Surgery
• Drugs – such as aspirin or NSAIDs

Intrinsic acute kidney injury refers to causes from direct damage to the kidneys. Examples include:

• Glomerulonephritis
• Acute interstitial nephritis (AIN)
• Acute tubular necrosis
• Drugs – such as gentamicin, certain chemotherapy drugs, tacrolimus
• Tumor lysis syndrome

Postrenal acute kidney injury refers to causes downstream from the kidney; often factors that lead to obstruction of the urinary tract or diseases that impair urine flow through the tract.

Examples include:

• Urinary tract obstruction
• Benign prostatic hyperplasia (BPH)
• Kidney stones
• Cancer
• Blood clots in the urinary tract

For your pharmacy license exam, you are expected to know this classification, what type of disease is classified as prerenal, intrinsic and postrenal etc. You are also expected to understand the various risk factors that lead to AKI.

These include:

• Diabetes type 2
• Hypertension
• Advanced age
• Hospitalization for a serious condition
• Heart failure
• Pre-existing kidney disease
• Established liver disease
• Cancer / certain cancer treatments

There are many different ways in which acute kidney injury may be diagnosed.

How is AKI Diagnosed?

The tests used to diagnose acute kidney injury depend upon what the clinician believes to be the most likely cause. However, the range of laboratory tests commonly used include:

• Urine output – reviewing urine production that passes each day
• GFR – establishing the degree of glomerular filtration rate
• Urine sample tests – establishing potential markers of disease
• Blood tests – measuring factors such as creatinine and BUN
• Biopsy – a sample may taken via a special needle for analysis
• Imaging – to identify kidney size, nephritic syndrome or systemic disease

The RIFLE criteria are often used to establish the severity of acute kidney injury.

These criteria range from (‘R’) Risk – 1.5x-fold increase in serum creatinine / or 25% reduction in GFR / or urine output <0.5mg/kg per hour for 6 hours – to ‘E’ or End-stage renal disease, referring to complete loss of kidney function for more than three months.

For your NAPLEX exam, you should also know these criteria.

Treatment / Complications

Treatment depends on:

• The cause of acute kidney injury
• Patient circumstances; established disease, age etc.
• How quickly the kidneys recover
• Whether any complications develop

Clinicians may recommend a special diet to limit the work the kidneys have to do. These recommendations may include:

• Low-potassium diet – foods of which include peppers, strawberries, apples and cauliflower. High potassium foods include bananas, spinach and tomatoes.
• Reduced salt diet – avoiding high salt foods / snacks helps to maintain adequate fluid balance and controls blood pressure to a greater extent.
• Reduced phosphorus diet – elevated phosphorus levels can lead to weaker bones and skin itch.

Complications of acute kidney injury include:

• Fluid imbalance – acute kidney injury can be caused by dehydration, or low blood volume, or the injury itself can lead to excess fluid overload. Complications are avoided by attending to these needs – either providing IV fluid to the patient or supplying a diuretic to remove excess fluid – restoring fluid balance throughout the body.
• Potassium balance – if they kidneys have malfunctioned, it increases the risk of hyperkalemia which, if left unchecked, can lead to cardiac arrhythmias. Potassium levels are monitored and medicines, such as Kionex, may be used to regulate those levels.
• Calcium balance – similarly, calcium levels may fall too low. In such cases, complications are avoided by addressing this imbalance by supplying calcium.
• Hemodialysis – in some cases, kidney function has entered a stage of decline where toxins accumulate to dangerous levels. In these cases, temporary hemodialysis may be needed to remove toxins before they contribute to further complications.

Even when the acute kidney injury resolves, patients are still advised to continue with a healthy diet. Suffering from an acute kidney injury increases the risk of developing another. It also increases the risk of serious cardiovascular events, too.

Register to one of our online courses today to receive instant access to clinical pharmacy questions on renal disease – covering the necessary detail you need to know. Check back to our blog soon for even more great articles to build your knowledge in preparation for exam day!