Kidney Failure & Urinalysis

Q: Urinalysis

The presence of specific excretory products in urine can be used in diagnostic tests for pregnancy and the use of performance-enhancing and recreational drugs.

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Kidney Failure

Kidney function is vital to survival and kidneys are so efficient that most people can live with only one. However, poor kidney function can eventually be fatal.

Causes of damage

Kidney disease, heart disease, hypertension (high blood pressure) and diabetes can cause damage to the kidneys requiring treatment.

Glomerular filtration rate (GFR)

Glomerular filtration rate (GFR) indicates how well the kidneys are functioning and estimates the amount of blood passing through the kidneys per minute.
- GFR decreases slightly with age but is markedly decreased if the kidneys are damaged.
  - Normal GFR: 90-100mL/min (90-100% kidney function) up to the age of 70 years.
  - Kidney failure: Less than 15mL/min (<15% kidney function).

Electrolyte balance

Kidney failure affects the balance of electrolytes in the body, most commonly causing:
- Hypervolemia (excess fluid).
- Hyperkalemia (excess potassium).
- Hyperphosphatemia (excess phosphate).
- Hypocalcemia (calcium deficiency).
- Bicarbonate deficiency.

Haemodialysis

Haemodialysis is a type of renal dialysis.
- Sessions happen in a clinic three times weekly and last 3-4 hours.
- A catheter is placed in a large vein in the groin or neck, or a more permanent fistula is created in the wrist or inner elbow.
- 200 mL of blood per minute passes through the dialyser (dialysis machine) and over membranes to exchange substances into the dialysate fluid.

Peritoneal dialysis

Peritoneal dialysis is another type of renal dialysis.
- A catheter is inserted into the abdomen.
- Dialysate fluid is pumped into the peritoneal cavity.
- Waste substances are removed from the blood by exchange into the dialysate across the membrane of the peritoneum.
This can be carried out overnight using an automated machine, or around four times a day with the manual exchange of waste fluid bags.

Kidney transplants

Kidney transplants are sometimes the only appropriate treatment for kidney failure.
- Long waiting lists and the possibility of organ rejection following transplantation means that patients do not always survive long enough for this treatment to work.

Urinalysis

The presence of specific excretory products in urine can be used in diagnostic tests for pregnancy and the use of performance-enhancing and recreational drugs.

Pregnancy testing

Human chorionic gonadotrophin (hCG) is a hormone which is only produced in the urine during pregnancy.
In pregnancy tests, mobile antibodies specific to hCG are attached to enzymes which can change the colour of a dye.
- These antibodies attach to the hCG and move along the test strip with the urine.

Pregnancy testing

More monoclonal antibodies specific to hCG are fixed in a line on the test, along with the substrate for the dye enzyme.
- If the hCG-antibody-enzyme complexes are formed, the enzyme changes the colour of the dye and shows a positive test line.

Anabolic steroids testing

In these tests, the ratio of testosterone to epitestosterone in the urine is measured.
- Increased testosterone levels relative to epitestosterone indicates anabolic steroid use, as normally these are roughly equal.
- This imbalance can remain in the body and be tested for between 14 and 28 days after anabolic steroids have been taken.

Other drugs

The use of many drugs can be detected through urinalysis through the presence of compounds produced when the liver metabolises them.
- Amongst others, these drugs include amphetamines, barbiturates, cannabinoids and cocaine.