Renal Failure Diagnostic Approach

Renal failure denotes loss of kidney functions. This could be acute or sudden or chronic or long term as a result of chronic kidney disease.

The diagnostic approach to both types of renal failures looks at both the possible underlying cause as well as the extent of renal damage.

Diagnostic approach to acute renal failure

• Detailed clinical history and physical examination to determine the possible cause. Physical examination involves ruling out dehydration along with systemic diseases.
• Urine analysis – urine is primarily tested for presence of red blood cells, blood and proteins.

In prerenal and post renal causes of acute renal failure, for example, decreased blood flow to the kidneys or obstruction of urine outflow, the urine contains no blood or protein.

In patients with glomerular disease the urine is strongly positive for blood and protein. If there is protein but little or no blood, it indicates tubular damage or interstitial disease. High levels of blood indicate cancer of the kidneys or large stones in the kidneys.

Urine is also tested for presence of white blood cells or nitrites that indicate urinary tract infections. Urine may also show presence of casts or crystals. Casts are cylindrical moulds of the tiny tubules of the kidneys. These may be cellular casts, granular casts or waxy casts.

• Urine output falls drastically in acute renal failure. There may be little or no urine output for 6 hours or less than 200 mL over 12 hours.
• Abnormal blood levels of electrolytes, including serum potassium, of more than 7.0 mmol/L or more than 5.5 mmol/L with ECG abnormalities.
• Blood levels of Creatinine are raised to more than 300 µmol/L. Blood levels of urea, blood urea nitrogen levels, urea Creatinine ratios etc. are also elevated.

Diagnostic approach to chronic kidney disease and chronic renal failure

• Screening for disease conditions that affect long term kidney functions including diabetes and blood glucose control, high blood pressure, taking kidney toxic drugs, heart disease, enlarged prostate, kidney stones etc.
• Blood is tested for creatinine, urea, urea Creatinine ratio, blood urea nitrogen etc. Blood is also tested for electrolytes and minerals like sodium, potassium, calcium, phosphates, magnesium etc.
• Checking the glomerular filtration rate of GFR - GFR is a measurement of waste fluids in millilitres that the kidneys can filter from the blood in a minute.

Normal GFR is over 90ml/min. Levels of blood Creatinine are measured. The estimated GFR or eGFR is calculated on the basis of serum creatinine using formulae. Normally eGFR of 50ml/min is same as 50% kidney function.

• Once the eGFR is determined, chronic kidney disease is staged. A five-stage system, based on eGFR levels is commonly used.

In stage 1 eGFR is normal or over 90 ml/min.

In stage 2 the eGFR has decreased slightly and is between 60 and 89 ml/min.

Stage 3, 4 and 5 are progressively deteriorating kidney functions based on eGFR. (stage 3 – 30 to 69 ml/min; stage 4 15-29 ml/min and stage 5 below 15 ml/min).

• Urine is tested for blood or protein.
• Imaging studies include ultrasound scan, a magnetic resonance imaging (MRI) scan or a computerised tomography (CT) scan that can help detect long term abnormalities like urine outflow problems, stones, abnormal shaped kidneys etc.
• A biopsy or small tissue sample is taken from the kidneys to examine under the microscope. This gives a confirmatory diagnosis of various types of kidney diseases.