Investigations and Diagnostic tests

Kidney disease is often not obvious in the early stages, and the onset may be insidious. If kidney disease is suspected, a few tests can be done to verify this, but it may come up in routine testing (for example, on admission to hospital). There are several tests that would be used in kidney disease for diagnostic purposes.

Urinalysis (Testing the Urine)

This is the most important test and is a very sensitive test for kidney damage. The appearance of the urine itself is important, (for example, blood in the urine may be obvious). The urine may be either concentrated (therefore darker) or dilute (and pale).

A “spot check” for detecting various substances in the urine may be made, and also for quantifying the degree of the substance present. A “Dipstix” is used and it is a sensitive indication of the presence and also the amount of protein, glucose and blood and ketones (if any) present in the urine.

• Protein is usually an indication of kidney disorders, but may occur after extreme exercise.
• Glucose (sugar) occurs in diabetes mellitus or when the threshold for glucose in the urine is lowered, such as in pregnancy.
• Blood may be a sign of a kidney stone, cancer, or infection for example.
• Ketones are the consequence of the breakdown of fat in the body, occurring as a result of diabetes mellitus (not controlled), and starvation.

Urine can also be examined under the microscope for white cells (which usually, but not always, indicate the presence of a urinary tract infection), red blood cells (if present, this is an abnormal result and almost always indicates glomerulonephritis), casts (small cylindrical bodies – red cell casts always indicate kidney disease), and bacteria (the presence of which, normally suggest a urinary infection).

Blood Pressure

Raised blood pressure can be either a cause or consequence of kidney disease. Ideally, blood pressure should be 120/80, the top figure, the systolic pressure (120) being the pressure measured when the heart is contracting, the bottom figure, the diastolic pressure (80) being the pressure when the heart is relaxing. People with kidney disease should aim to keep their blood pressure at less than 130/80, using treatment including medication, if possible.

Kidney function Tests

• Serum creatinine – This is a good guide to kidney function. Creatinine is a waste product from muscles, the production of creatinine in the body is more or less constant, and it is almost completely filtered out in the kidney. If the kidney is damaged, the creatinine is not filtered and the blood pressure rises. The normal serum creatinine is 79-118 microMol/litre.
• Creatinine clearance – This is also a measure of kidney function. It can be calculated using a formula, and it compares the amount of creatinine in the blood with the amount excreted in the urine. This normally involves collecting urine over a 24- hour period, and also involves a blood test being taken at the same time. Normal creatinine clearance is 80-120ml/minute. Lower levels indicate kidney disease.
• Plasma urea measurement - Plasma urea also indicates kidney function the normal plasma urea value is 2.5 to 6.7 mmol / Litre.

Kidney imaging tests

• Abdominal X-Ray

A plain X-Ray of the abdomen is not normally used as a diagnostic procedure now, but it will show up stones, if present.

• Kidney Ultrasound (This is the most common test)

This is a non- invasive procedure, and does not use ionising irradiation. Ultrasound can be used to assess the size and structure of the kidneys, as well as other structures in the abdomen. It also shows up masses, cysts, tumours and stones. It is used to diagnose obstructive uropathy, and obstruction, and the findings of two small kidneys indicates irreversible damage. It can be used to guide biopsy needles, when a biopsy of the kidney tissue is necessary.

• Computerized Tomography (CT) Scanning

This is especially useful in looking at kidney masses and stones. It can be used with or without contrast medium. It is particularly useful in showing up kidney and adrenal gland masses.

• Magnetic Resonance Imaging (MRI) Scanning

MRI scanning techniques can provide 3 – dimensional pictures of structures, and is non- invasive.

• Intravenous Pyelography (IVP)

This is also known as Excretion Urography or Intravenous Urography.

The patient is given an intravenous injection of iodine- containing contrast medium, which shows up on X-Ray, and is excreted by the kidneys. The contrast medium on X-Ray film demonstrates the size and outline of the kidneys, and the collecting system of the kidneys, the ureters and bladder. A series of X-Rays (radiographs) are taken at intervals after the injection. Its main benefit is showing up the collecting system of the kidneys, stones, and any malignancy of the bladder and ureters. The disadvantage to this investigative procedure is that a small proportion of the population suffer an allergic reaction to the contrast medium.

Click here for: Image of Intravenous Pyelogram (IVP) showing hydronephrosis and dilated calyx of the Right kidney

• Radionuclide scanning

A radioactive substance known as “DMSA” is injected intravenously, and is taken up and excreted by the kidneys, and this is picked up by a gamma camera; this allows the function of the kidneys, (as well as size and shape) to be monitored.

• Angiography

Small doses of contrast medium are injected, and are mainly used to define arterial disease in or near the kidney. It is still the main means of visualizing the renal artery.

Kidney Tissue Biopsy

This helps identify the cause of kidney damage. Biopsy (tissue sample) of the kidney tissue is taken through the skin and muscles of the back, using ultrasound, or CT scanning as a guide for the biopsy needle.

The patient lies face down, and holds his/ her breath at the moment the biopsy is taken. A local anaesthetic is used in the skin prior to the needle being inserted. The tissue is stained and examined under a microscope, or an electron microscope.

Biopsy is used to enable the glomeruli to be looked at, in suspected renal failure, suspected rejection of a transplanted kidney, and in systemic diseases of the body, which may involve the kidney.

The main complication is bleeding. It should not be performed on small, scarred kidneys.

Amended April 2008