Tests performed on samples of your blood and urine are the first step in the investigation of kidney problems. Tests of these types can show how well the kidneys are removing excess fluids and waste. When changes in the shape or size of the kidney, bladder or urinary tract are suspected, a variety of imaging tests can be used. A sample of kidney tissue, a biopsy, is sometimes helpful in diagnosing the specific cause of the problem.
Tests commonly used for screening and diagnosis ― There are several tests commonly used to help the healthcare professional recognise if you have kidney or urinary disease. A blood sample can be analysed for creatinine (and estimated glomerular filtration rate [eGFR]) and urea. The level of these waste products in the blood increases as kidney filtration declines. Abnormal results are usually the first sign that kidney disease is present. A urine sample is typically also examined and analysed (urinalysis) as part of routine screening. This set of tests looks for indicators of kidney and urinary disease such as red blood cells, white blood cells (WBCs or leukocytes), and protein in the urine. If you have diabetes or high blood pressure, you should have estimated GFR and urine albumin/creatinine ratio checked annually to detect kidney disease in its early stages. If you are a current smoker, are obese, have established CVD, a family history of chronic kidney disease or are of Aboriginal or Torres Strait islander origin and are aged 35 years or older you should have estimated GFR and urine albumin/creatinine ratio checked every two years. When you have symptoms suggesting infection, a urine culture can confirm the presence of a bacterial infection.
Tests to monitor kidney function ― If you have been diagnosed with a kidney disease, your health care provider will request laboratory tests to help monitor kidney function. Blood levels of urea, creatinine and estimated GFR are measured from time to time to see if the kidney disease is getting worse. The amount of calcium and phosphate in the blood and the balance of serum and urine electrolytes can also be measured, as these are often affected by kidney disease. Haemoglobin, measured as part of a full blood count (FBC) may be measured (the kidneys make a hormone, erythropoietin, that controls red blood cell production). Urine albumin/creatinine ratio can be used to test the effects of treatment in diabetes and Urine total protein in nephrotic syndrome (a condition where the kidneys leak large amounts of protein into the urine). Parathyroid hormone, which controls calcium levels, is often increased in kidney disease and it may be checked to see if bone damage is developing that requires treatment.
Imaging techniques ― If blockage to the flow of urine or kidney damage which might alter the shape or size of the kidney or urinary tract is suspected, a picture of the kidneys can be helpful. Imaging techniques such as an ultrasound, CT scan (computed tomography), isotope scan, or intravenous pyelogram (IVP) may be used. Various x-ray procedures can also be employed, such as: an intravenous urogram, micturating cystogram (picture whilst passing urine), or renal arteriogram (which looks at the flow of blood in the kidney).
Kidney biopsy ― A biopsy can determine the cause of protein or blood in the urine. Analysing a small piece of kidney tissue can reveal the nature and extent of structural damage to a kidney. A biopsy, obtained using a biopsy needle and diagnostic imaging equipment, is often useful when disease of the glomerular filter is suspected.