Symptoms and diagnosis

Early signs of kidney disease (nephropathy) or toxicity include elevated levels of the protein creatinine in the blood, reduced rates of creatinine removal from the blood, and the presence of sugar or protein in the urine.

In more serious cases, drug toxicity may cause Fanconi syndrome, a disorder in which the proximal tubules are unable to properly reabsorb electrolytes and nutrients, leading to low phosphate levels in the blood and abnormally high acidity. Nephrogenic diabetes insipidus is a condition in which the kidneys produce an excessive amount of urine, up to several litres per day, causing so much water loss that the body becomes dehydrated.

Symptoms of kidney impairment may include extreme thirst, excessive or sparse urination, painful or difficult urination, urinary urgency, pain in the flanks, fatigue, rapid heart rate, high blood pressure, and muscle pain or weakness.

Kidney toxicity is diagnosed using laboratory tests to assess the level of kidney function – i.e., their ability to remove waste products such as creatinine from the blood. The presence of protein in the urine is indicative of kidney damage. Elevated serum creatinine levels are also an indication of impaired kidney function, but diagnosis is generally based on more sophisticated measures derived from raw serum creatinine levels. The most accurate indicator is the glomerular filtration rate (GFR). Several equations can be used to calculate an estimated GFR value from the patient's serum creatinine level, age, sex, race, weight and body size; the Cockcroft-Gault formula and the Modification of Diet in Renal Disease (MDRD) formula are the most commonly used.¹

The creatinine clearance rate can also be derived from serum and urine creatinine levels by collecting urine over a 24-hour period. A creatinine clearance rate below 50 ml/min indicates significant kidney impairment.

Suspected kidney damage may also be assessed using ultrasound or computerised tomography (CT) scans and by the removal and analysis of a small sample of kidney tissue.

Chronic kidney disease (CKD) is generally defined as either a GFR < 60 ml/min per 1.73 m², or kidney damage (as shown by protein in the urine or evidence of damage from biopsy or imaging), persisting for over three months.