Renal Function Tests: Focus on Renal Blood Flow Substances

One of the most commonly dreaded conditions is kidney dysfunction.

How could we assess if our kidney is functioning normally? We have our blood tested, among others.

There are several ways to test for proper kidney function: Glomerular Filtration Rate tests (GFR), Tubular secretion and reabsorption tests, concentration and dilution tests and Renal Blood Flow tests (RBF).

This article will deal more on the RBF tests. There are 3 substances involved in the RBF tests. These are creatinine, BUA and BUN. These 3 should be present in blood within their normal ranges. They are usually elevated or above their normal levels when there is kidney dysfunction.

The following are these substances:

1. Blood creatinine

Creatinine is a substance coming from the breakdown of creatine during muscle

metabolism. It is a substance that is not reabsorbed by the kidneys and is excreted by the kidney at a constant rate.

Any dysfunction of the kidneys, specifically the Glomerular Filtration Rate (GFR) function will cause an abnormal result in the person's blood creatinine, urine creatinine or creatinine clearance tests.

Excessive muscular exertion or strenuous exercises are not allowed before the performance of the blood test as it would falsely elevate the test results.

2. Blood urea nitrogen (BUN)

Urea nitrogen is the end product of protein metabolism. Examples of protein containing foods are meat, soya beans; BUN however is not specific only for the kidneys. It is elevated also in various conditions like starvation, burns, shock and many more.

3. Blood uric acid (BUA)

Uric acid is the breakdown product of purine. Purine comes from what we eat, like legumes, sardines, kale, visceral organs, etc.

The elevation of blood uric acid (uricemia), the deposition of uric acid in the joints (gouty arthritis /tophi) and in the kidneys ( nephrolithiasis), is what we call in general, gout.

This happens when the kidneys could not properly excrete the uric acid coming from the purines in our diet.

Drinking alcohol could exacerbate the condition as alcohol affects the pH of urine. Uric acid could not be excreted in alkaline urine, so they are deposited in the joints and kidneys and eventually form stones.

Men are also more prone to the above mentioned conditions because of their lifestyle and drinking habits.

Fasting (8-12 hours) is observed because of uric acid coming largely from our diet.

All these substances in blood are considered as the markers for kidney function so they are called Kidney Function Tests (KFT) or Renal Function Tests (RFT); and are three of the most common laboratory assays performed in the clinical laboratory.

Their normal values depend on the method used, but generally for blood creatinine it is 0.8 to 1.4 mg/dL. For BUN - it is 8 to 20 mg/dL and for BUA, it is 2 to 6 mg/dL for females and 3 to 7 mg/dL for males.

Any significant increase or decrease in these values of the three parameters would indicate a kidney dysfunction. Creatinine test is a more sensitive test than BUN for KFT because it is elevated only when there is significant loss of kidney function.

So if you would like to know if your kidney is functioning normally, have these three parameters tested in your blood and be aware of their clinical significance in your health.