7.11 Monitors of Kidney Failure/Prevent Dialysis 3

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11. Monitors of Kidney Failure – Update 24 Aug. 2021

A simple monitor is Dipstick monthly testing of protein in urine as previously mentioned.

The G(lomerular) F(iltration) R(ate) is gold standard of kidneys failure. Recall that the kidneys are filtration and secretion/re-absorption organs made up of millions of micro units. Each unit, or nephron, has a glomerulus and its micro tubule. The glomerulus is a circular structure where a terminal renal arteriole is folded up and pressed against a tuft of tubule. The arteriole is separated from tubule excretory fluid by thin membrane; the hydraulic positive pressure from arterial blood pressure causes water and small molecules in arteriole blood to filter across into the tubule. The total amount of fluid of blood filtered per minute into the tubules summed from all of the millions of nephrons in your two kidneys is your GFR (Glomerular Filtration Rate), and it is expressed as milliliters per minute (ml/min).

   GFR is key measurement; all decisions on dialysis are based on a schedule of GFR fall from normal, and its rate of fall will predict symptoms and dying from kidneys failure and when to start moving on renal function replacement.

   The GFR is either reported as volume rate (ml/min) as measured or it is reported as “corrected” for standard body surface area (BSA) 1.73 meter². Nephrologists use the directly measured GFR but you may see the GFR given as per 1.73 m² in textbook because it is useful in population comparison.

   In practice, nephrologists use the easily done blood test Creatinine (Cr) in place of the GFR in decision-making about End Staging of dialysis. The normal Cr is between 0.6 and 1.3 mg/dL. Creatinine comes from muscle; men have higher Cr than women and any muscle exercise or injury or recent surgery or an epileptic fit will raise the Cr number while low protein diet will drop it. It is also sensitive to meat eating. So the blood drawing should be standardized to morning after overnight fast, no recent illness or heavy exercise or accident or surgery, and no heavy meat eating.

   The Blood Urea Nitrogen (BUN) is another test of kidneys function. It is the nitrogen end-product of protein metabolism excreted mostly by kidney filtration. Creatinine is more accurate for this purpose and focused on here.

Imaging of kidneys is another monitor. Ultrasound is ideal; no damaging radiation, low cost and easy repeat. It can show cyst, blockage, and stage of kidney damage by kidneys sizes, and good view of lower urinary tract. If biopsy of kidney is planned, ultrasound guidance makes it safer and more accurate. Biopsy of kidney is key to definitive diagnosis. In expert hands under ultrasound guidance the risk is low. The procedure is done by passing a biopsy needle from skin surface into a kidney, obtaining several samples that are subjected to various tests. Biopsy should be done at start of investigation of kidneys failure, after at least 2 weeks of no aspirin or other anti blood clot med and shortly after normal blood clot tests.

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