Question

Case Study:

A 62-year-old man with chronic kidney disease secondary to diabetes mellitus is reviewed.

What is the difference between acute and chronic kidney injury?

Explain what diagnostic tests can help to identify kidney injury?

Explain how Chronic Kidney Disease may be classified according to GFR?

Name the variables to affect the estimated glomerular filtration rate (eGFR).

Answer 1

1.Accute renal failure (ARF) is a sudden loss of kidney function caused by renal cell damage f\rom ischemia or toxic substances.Acute renal failure occurs occurs abruptly and can be reversible..Acute renal failure occurs abruptly and can be reversible.Acute renal failure leads to hyperperfusion, cell death and decompensation in renal function.The prognosis depends on cause and condition of the patient.Near normal or normal kidney function may resume gradually.

Chronic renal failure,CRF is a progressive loss of kidney function. It is charecterised by glomerular filtration rate of less than 60 ml/min for period of 3 months longer. Chronic renal failure is irreveersible and results in uremia or end stage renal disease Chronic renal failure requires dialyss or kidney transplantation to maintain life

2,

,is primarily diagnosed by blood and urine tests. Among the many lab tests used to evaluate kidney function, there are two key measures central to the diagnosis and management of kidney fsaailure.

Serum Creatinine

Serum creatinine (SCr) measures the amount of a substance called creatinine in the blood. Creatinine is a by-product of muscle metabolism that is excreted in urine. Because it is produced and excreted at a fairly steady rate, it is a reliable measure of kidney function and is a key indicator of kidney failure.

Normal SCr levels in adults are:

• Approximately 0.5 to 1.1. milligrams (mg) per deciliter (dL) in women
• Approximately 0.6 to 1.2 mg/dL in males

Urine volume simply measures the amount of fluid you urinate over a given period of time. As ARF is defined by the loss of kidney function, the value—measured in milliliters (mL) per kilograms of your body weight (kg) per hour (h)—is central to confirming kidney impairment and measuring your response to treatment.

Oliguria, the production of abnormally small volumes of urine, is defined as anything less than 0.5 mL/kg/h.3

Other Lab Tests

Other lab tests used to diagnose ARF include:

• Blood urea nitrogen (BUN) measures the amount of a waste product in the blood called urea nitrogen. Urea nitrogen is created when the liver breaks down protein and, like serum creatinine, is produced and excreted in the urine if fairly consistent volumes. High BUN levels are indicative of ARF and may also suggest the underlying cause of the kidney failure (such as heart failure, dehydration, or urinary tract obstruction).
• Creatinine clearance measures creatinine level in both a sample of blood and urine sample collected over 24 hours. The combined results can tell us how much creatinine is being cleared from the blood through urination as measured by mL per minutes (mL/min). A normal creatinine clearance is 88 to 128 mL/min in women and 97 t0 137 mL/min in men.
• Estimated glomerular filtration rate (eGFR) is a blood test that estimates how much blood is passing through the natural filters of the kidneys, called glomeruli. The speed by which this happens can tell us how much the kidneys have been damaged from stage 1 (minimal to no loss of kidney function) right through stage 5 kidney failure.
• Serum potassium is used to determine whether there is excess potassium in the blood (a condition known as hyperkalemia). Hyperkalemia is characteristic of ARF and, if left untreated, can lead to severe and potentially life-threatening dysrhythmia (abnormal heart rate).
• Urinalysis is simply a lab analysis of the make-up of your urine. It can be used to detect whether there is excess protein in the urine (​proteinuria), considered a key feature of ARF. It can also detect blood in the urine (hematuria) which may occur if the ARF is caused by some sort of kidney damage or urinary tract obstruction.

Imaging Tests

In addition to blood and urine tests, imaging tests may be used to detect if there is any sort of kidney damage or if there is an impairment to either the flow of blood to the kidney or the excretion of urine from the body.

Among some of the tests used:

• Ultrasound is the preferred method of imaging testing and can be used to measure the size and appearance of the kidneys, detect tumors or kidney damage, and locate blockages in the urine or blood flow. A newer technique called a Color Doppler can be used to assess clots, narrowing, or ruptures in the arteries and veins of the kidneys.
• Computed tomography (CT) ​is a type of X-ray technique that produces cross-sectional images of an organ. CT scans can be useful in detecting cancer, lesions, abscesses, obstructions (such as kidney stones), and the accumulation of fluid around the kidneys. They are standardly used in obese people in whom an ultrasound may not provide a clear enough picture.
• Magnetic resonance imaging (MRI) ​uses magnetic waves to produce high-contrast images of the kidneys without radiation.

Kidney Biopsy

A biopsy involves the removal of organ tissue for examination by the lab. The type typically used to assess kidney disease is called a percutaneous biopsy in which a needle is inserted into the skin and guided into a kidney to remove a sampling of cells.

Biopsies are most often used to diagnosed intrinsic ARF (acute renal failure caused by damage to the kidneys). The biopsy can quickly diagnose some of the more common causes of kidney damage, including:

• Acute interstitial nephritis (AIN), the inflammation of tissue between kidney tubules
• Acute tubular necrosis (ATN), a condition in which kidney tissues die due to the lack of oxygen
• Glomerulonephritis, the inflammation of glomeruli in blood vessels of the kidneys

3. CKD is classified based on the eGFR and the level of proteinuria and helps to risk stratify patients.

Patients are classified as G1-G5, based on the eGFR, and A1-A3 based on the ACR (albumin:creatinine ratio) as detailed below.

For Example

• A person with an eGFR of 25 ml/min/1.73 m2 and an ACR of 15 mg/mmol has CKD G4A2.
• A person with an eGFR of 50 ml/min/1.73 m2 and an ACR of 35 mg/mmol has CKD G3aA3.

It is important to note that patients with an eGFR of >60 ml/min/1.73m2 should not be classified as having CKD unless they have other markers of kidney disease (see above*).

GFR category G2 may be over diagnosed by eGFR because equations used to estimate GFR may give falsely low results in people with near-normal function. See measurement of renal function

Patients with CKD can be classified depending on their level of kidney function, or eGFR, and the amount of protein present in the urine. This information forms the basis of CKD staging which is useful for planning follow up and management. The higher the stage (G1->G5) and the greater the amount of protein present in the urine (A1->A3) the more “severe” the CKD.

4.

A person's GFR decreases with age and some illnesses and usually increases during pregnancy.

A slightly different equation should be used to calculate the eGFR for those under the age of 18 (see below). The eGFR equations are not valid for those who are 70 years of age or older because muscle mass normally decreases with age.

An eGFR may not be as useful for those who differ from normal creatinine concentrations. This may include people who have significantly more muscle (such as a body builder) or less muscle (such as a muscle-wasting disease) than the norm, those who are extremely obese, malnourished, follow a strict vegetarian diet, ingest little protein, or who take creatine dietary supplements.

The eGFR may also be affected by a variety of drugs, such as gentamicin, cisplatin, and cefoxitin that increase creatinine levels, and by any condition that decreases blood flow to the kidneys.

The calculation for eGFR is intended to be used when kidney function and creatinine production are stable. If a creatinine level is measured when the kidney function is changing rapidly, such as with acute kidney failure, then it will not give a useful estimate of the filtration rate.

Estimated GFR results are reported as milliliters/minute/1.73m2 (mL/min/1.73m2). Because some laboratories do not collect information on a patient's race when the sample is collected for testing, they may report calculated results for both African Americans and non-African Americans. The healthcare practitioner uses the result that applies to the particular patient in order to interpret the results correctly.

A normal eGFR for adults is greater than 90 mL/min/1.73m2, according to the National Kidney Foundation. (Because the calculation works best for estimating reduced kidney function, actual numbers are only reported once values are less than 60 mL/min/1.73m2).

An eGFR below 60 mL/min/1.73m2 suggests that some kidney damage has occurred. The test may be repeated to see if the abnormal result persists. Chronic kidney disease is diagnosed when a person has an eGFR less than 60 mL/min/1.73m2 for more than three months.

A person may have some kidney damage even with an eGFR greater than 90 mL/min/1.73m2. Other evidence, such as increased urine albumin, may indicate some degree of kidney damage. Thus, a person's eGFR should be interpreted in relation to the person's clinical history and presenting conditions.