Investigation for Chronic Kidney Disease

Urinalysis
Testing of urine is a basic test for the presence and severity of kidney diseases. 24-hour-collection is a general investigation for kidney diseases. The collected urine is then analysed through dipstick, or microscopy.

What to look for?
- Clear / cloudy?
- Colour change
>>>large amount of RBC stains urine pink or red i.e. haematuria
- Urine pH
>>>normal pH between 4.6 – 8
- Urine volume in 24 hours
- Presence of haemoglobin / glucose / protein / leucocyte esterase / nitrites / ketones / creatinine
>>>the above substances is sometimes present in small quantities in the normal population
>>>protein : creatinine ratio is almost as accurate as 24hr urine collection in diagnosing nephrotic syndrome
- Casts / lipids / organisms can be identified through urine microscopy

Any positive findings should be further investigated as they can be transient, of no prognostic importance, or indicative of other diseases. Other evidences of renal disease e.g. abnormal renal function, or clues from patient’s history, examination etc. should be taken into account for the diagnosis.

Blood test
- Blood urea nitrogen (BUN) & serum potassium increase in kidney diseases
- Serum creatinine increases due to decrease excretion via urine in kidney diseases

Glomerular Filtration Rate
The functional unit of kidneys, nephrons, is responsible for the controlling the amount of substances that stay in plasma or excreted via urine. To assess the renal excretory capacity, the ideal substance should be freely filtrated across the glomerulus, neither reabsorbed nor excreted into renal tubules, in a steady state concentration in plasma, and easily and reliably measured – which, does not exist.
Creatinine is universally used for the test, despite its varying concentration with diet, gender, muscle mass etc. With an impaired renal function there is correspondingly more tubular creatinine secretion, while a fall in GFR.

Renal imaging
Ultrasound is by far the most commonly used technique for screening and investigation. The imaging provides information of:
- Renal size, which is usually in proportion to body weight, between 9 - 12cm
- Shape, symmetry of kidneys
- Renal cysts, tumour, stone, obstruction
Small kidneys are noted in person with chronic renal disease.

Contrast study of kidneys is less common as person with pre-existing renal impairment, advanced age, diabetes etc. have an increased risk of contrast-induced nephropathy.

Renal biopsy
This is a highly specialized investigation to diagnose renal disease, especially when person presents with unexplained reduction in renal function. The test however, should only be performed after careful consideration of the risk to benefit ratio.