Assessment of kidney function

Kidneys perform many vital functions, including removing metabolic waste products from the bloodstream, regulating the body's water balance, and maintaining the acidity/aI kalinity of the body fluids.

Some conditions lead to the decline in kidney function which results in a build-up of toxic waste substances in the blood. A number of tests help to determine if the kidneys are performing adequ ately. They are collectively called the kidney function tests. These tests are done on urine samples, as well as on blood samples

Urine tests

Routine urinalysis:
A simple, screening test administered when kidney problems are suspected. A small quantity of urine sample collected is examined:

• Physically for colour, odour, appearance, and concentration
• Chemically for substances such a protein, glucose
• Microscopically for the presence of cellular elements, bacteria, crystals, and casts

Urine protein test
Healthy kidneys filter all proteins from the bloodstream and then reabsorb them, allowing only little protein, into the urine.

The persistent presence of significant amounts of protein in the urine is an important indicator of kidney disease. A 24-hour urine test is done to know how much urine the body is producing in a day or how much of a particular substance is eliminated in a day. Patients will have to collect alI their urine produced in a 24-hour period.

This test helps to evaluate:

• Creatinine
• Hormone (5-HIAA) in order to exclude carcinoid syndrome
• Urine excretion of copper to exclude Wilson's disease

A 24-hour urine sample shou Id contain less tha n 150 mg of protein.

Microscopic analysis
In this test, urine is spun in a centrifuge so the solid materials settle down. The sediment is spread on a slide and examined under a microscope.
Types of materials that may be found include:

• Red or white blood cells - Normally blood cells are not found in urine. Presence of blood cells are a sign of infection, cancer, injury or kidney disease.
• Casts - Kidney disease can cause plugs of material such as red or white blood cells, waxy or fatty substances, or protein (called casts) to form tiny tubes in the kidneys. The type of cast can provide clues about the type of kidney disease that may be present.
• Crystals - Indicate kidney stones
• Bacteria, yeast cells, or parasites - Indicate an infection

Urine Culture & Sensitivity test
The Urine culture is the method to grow and identify bacteria that maybe present in the urine. The sensitivity test helps to identify the best medicine to treat the infection.

Urine Sugar Test
Normally there is very little or no g lucose in urine. When the blood sugar level is very high, as in uncontrolled diabetes, it spil Is over in to the urine.

• Urea clearance:
  It is a test which uses a blood specimen to determine the level of urea present in the blood and two urine samples, the second being collected one hour after the first urine sample. This test detects how much urea is filtered by the kidneys into the urine.
• Creatinine clearance test:
  Creatinine is a waste product of muscle energy metabolism. Because the body does not recycle it, all of the creatinine filtered by the kidneys is excreted in the urine, making creatinine clearance a very specific measurement of kidney function

Blood Test

• Blood Urea Nitrogen(BUN):
  It is a blood test which assesses kidney function. Urea is a by-product of protein metabolism and is formed in the liver. Urea is filtered from the bolld by the kidneys and excreted in the urine.
• Creatinine test:
  Creatinine leaves the muscle and enters the blood, where it is removed by the kidneys. Most of the creatinine enters the urine after being filtered by the glomeruli and the remaining amount accumulates in the serum or plasma.