Kidney Failure and Detection in Urine

When the kidneys fail, the body rapidly loses its ability to regulate water, solute concentrations, blood pH, and nitrogenous waste. Without intervention, kidney failure is fatal within days. Modern medicine offers several life-saving options — haemodialysis, peritoneal dialysis and transplantation — each with its own advantages and limitations. Urine is also used as a diagnostic tool: its composition reveals information about kidney function, metabolism, pregnancy, drug use and disease. This final lesson covers causes and treatment of kidney failure, and common uses of urine analysis, matching OCR A-Level Biology A specification module 5.1.2(i)–(j).

Key Definitions:

• Kidney failure — the loss of kidney function, classified as acute (sudden) or chronic (progressive).
• Dialysis — a procedure that filters blood artificially, removing wastes and excess water when the kidneys cannot.
• Haemodialysis — dialysis in which blood is passed through an external machine.
• Peritoneal dialysis — dialysis in which the peritoneal membrane in the abdomen is used as the dialysis surface.
• Monoclonal antibody — an antibody produced by a single clone of B-cells, specific for a single epitope; used in diagnostic tests.

---

Causes of Kidney Failure

Kidney failure can be acute (developing over hours or days) or chronic (developing over months or years). OCR expects you to know several main causes:

Diabetes Mellitus

Diabetes — particularly type 2, which is becoming more prevalent — is the leading cause of chronic kidney failure worldwide. Persistently high blood glucose damages the glomerular capillaries and the basement membrane over many years. This is called diabetic nephropathy and begins with leakage of protein (albumin) into the urine, progressing to reduced GFR and ultimately complete failure.

Hypertension (High Blood Pressure)

Chronic high blood pressure damages the small vessels of the glomeruli. Thickening and narrowing of these vessels reduces filtration and eventually destroys nephrons. Hypertension and diabetes together account for the majority of cases of chronic kidney disease.

Infections

• Pyelonephritis — bacterial infection of the kidney, often spreading up from the bladder (especially in women), causing inflammation and scarring of the nephrons.
• Glomerulonephritis — inflammation of the glomeruli, often triggered by an immune response after infection with certain streptococci. Immune complexes deposit in the basement membrane, damaging the filtration barrier.

Other Causes

• Obstruction of urine flow — kidney stones, prostate enlargement, tumours. Prolonged obstruction damages the kidney by back-pressure.
• Trauma or haemorrhage — a sharp fall in blood pressure reduces blood flow to the kidneys, causing acute tubular necrosis.
• Toxins — heavy metals, some drugs (especially NSAIDs and certain antibiotics in overdose), and contrast dyes used in imaging.
• Genetic diseases — polycystic kidney disease, in which cysts replace functional kidney tissue.

The Consequences

As kidney function declines, the following problems develop:

• Build-up of urea and creatinine (uraemia), leading to nausea, fatigue and mental confusion.
• Fluid overload — fluid accumulates in lungs (pulmonary oedema) and legs (peripheral oedema).
• Acidosis — inability to excrete H⁺ drops blood pH.
• Hyperkalaemia — high blood K⁺ causes dangerous cardiac arrhythmias.
• Anaemia — reduced production of erythropoietin, the hormone that stimulates red blood cell production.
• Bone disease — reduced activation of vitamin D affects calcium handling.

Below about 10 % of normal function, dialysis or transplantation is required for survival.

---

Treatment of Kidney Failure

Haemodialysis

In haemodialysis, blood is removed from the patient (usually via an arteriovenous fistula in the arm), passed through a dialyser, and returned. Inside the dialyser, blood flows through many fine tubes made of a partially permeable membrane, while dialysis fluid flows over the outside in the opposite direction — a countercurrent exchange.

• The dialysis fluid contains normal concentrations of glucose, Na⁺, K⁺ and other useful ions. It contains no urea and no creatinine.
• Waste products (urea, creatinine) therefore diffuse from the blood into the dialysis fluid down their concentration gradient.
• Excess water is removed by applying a positive pressure to the blood compartment.
• Useful substances do not diffuse out because they are already at equal concentration on both sides.

A haemodialysis session typically lasts 3–5 hours and must be carried out three times a week. Patients must restrict their fluid and protein intake between sessions to prevent overload. Life expectancy on dialysis is much shorter than with a functioning transplant.

flowchart LR
    A[Patient's blood<br/>high urea] --> B[Dialyser]
    B --> C[Cleaned blood<br/>low urea]
    C --> A
    D[Dialysis fluid<br/>no urea] --> B
    B --> E[Waste fluid<br/>with urea]

Peritoneal Dialysis

In peritoneal dialysis, the patient's peritoneum (the thin, richly vascularised membrane lining the abdominal cavity) is used as the dialysis membrane. A permanent catheter is inserted through the abdominal wall. Sterile dialysis fluid is run into the peritoneal cavity, where it is left for several hours. Waste products diffuse from the peritoneal capillaries into the fluid across the membrane. The fluid is then drained out and replaced with fresh fluid.

• Can be done at home by the patient.
• Less disruptive than haemodialysis — often carried out overnight with a machine that cycles fluid automatically.
• Risk of infection (peritonitis) is the main complication.
• Less effective than haemodialysis for patients with very high protein catabolism.

Kidney Transplantation

The gold standard treatment. A healthy kidney from a donor (living relative or deceased organ donor) is implanted in the lower abdomen, with its artery, vein and ureter connected to the recipient's vessels and bladder.

Advantages:

• Restores near-normal kidney function.
• Freedom from the time commitment of dialysis.
• Better long-term survival and quality of life.

Disadvantages:

• Shortage of donor organs; long waiting lists.
• Requires lifelong immunosuppressive drugs to prevent rejection, which increase infection and cancer risk.
• Major surgery with its own risks.
• Rejection can still occur, eventually requiring a return to dialysis.

Ethical considerations: opt-in vs opt-out organ donation schemes; living donors; the risk to a relative of donating a kidney; the equitable allocation of scarce organs.

Comparison