Understanding Your Urinalysis
Kidney disease, specifically lupus nephritis, is one of the most common and serious conditions for those diagnosed with lupus. Timely urinalysis testing is a relatively simple and effective way to help with an early diagnosis that may prevent damage later on. Here is an overview of what you should know and expect from urinalysis testing.
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Introduction
Lupus or SLE is an incredibly difficult to diagnose condition and can affect almost any part of the body. One type of lupus, lupus nephritis (LN), specifically attacks the kidneys and can lead to serious, even life-threatening symptoms. It is estimated that up to 60% of all adults and 80% of children with lupus will develop some form of kidney involvement or damage. Yet, the vast majority of those will not be diagnosed with kidney disease at the beginning of their disease.
Urinalysis testing measures the physical, chemical and microscopic characteristics of urine. Within this examination are the indicators for kidney functions or damage that might suggest lupus nephritis or other lupus related conditions. The most common indicators for lupus nephritis involve the presence of certain proteins, blood cells, kidney cells, even bacteria that can result from kidney damage.
Unfortunately, most of these indicators alone do not provide a definitive diagnosis for SLE or lupus nephritis and blood tests as well as invasive biopsies of the kidneys are needed. Currently, a great deal of research has gone into finding new indicators, called biomarkers that could help make the diagnosis of LN cheaper, quicker and far less invasive. Before exploring the techniques and details of urinalysis testing, here is a brief overview of the renal system and how lupus can affect them.
Lupus and the Kidneys
The kidneys are just one part of the body’s urinary system, otherwise known as the renal or excretory system. The primary job of the urinary system is to filter the blood and remove any excess water, electrolytes, and any metabolic wastes (urea) that would be unhealthy and ultimately deadly if they remained in the body. How this happens is both simple and incredibly complex and requires some of the most delicate tubes and blood vessels in human anatomy. It is far too complicated to describe here, but it entails structures, called glomeruli, which filter chemicals, molecule by molecule, from the blood and mixes them with water to form urine. A complex series of tubules take the urine through several pathways and eventually lead to ureters, which in turn bring the resulting urine to the bladder. There the urine is stored until it is eliminated through the urethra.
There are approximately one million glomeruli in each kidney and they are the most delicate and important part of its anatomy. They are also where most of the damage from lupus nephritis (or most other kidney diseases) takes place. The microscopic blood vessels and tube-like structures within each glomerulus can be damaged by lupus in several ways. These include inflammation, blood clots (often from vasculitis) as well as other types of damage that are associated with the body’s out of control autoimmune response. When this occurs, the kidneys lose their ability to filter the blood properly, and other parts of the blood can leak into the urine. These leaked chemicals and cells are most of what is measured with urinalysis.
The Urinalysis Test and Parameters
The urinalysis begins with the relatively simple sampling method of peeing into a cup. This most often happens in the healthcare practitioner’s office or a clinic and the only really important part is to make sure that the sample is not contaminated – particularly if the sample is to be cultured for bacterial infections. For several urine tests, it is possible to buy over-the-counter tests for use at home.
Also, it is important to know that the results from a urinalysis can indicate any kind of nephritis (inflammation of the glomeruli or nephrons) with many possible causes, so these are not enough to make a positive lupus nephritis diagnosis by themselves.
Physical Analysis: Once the urine sample makes it to the lab, a great number of tests are conducted. These include a physical examination (or macroanalysis) of the color, clarity, and specific gravity of the urine.
Color: Many things can affect the color of urine without indicating kidney disease, including the amount of water you drink (your level of hydration) as well certain kinds of food and medications that you might take. So, color is a very general test and not diagnostic.
Clarity: The clarity of urine is usually described as clear, slightly clear, cloudy or turbid. If urine is cloudy, it is usually an indication of excessive amounts of protein, cellular material or infection, but just as with color more chemical and microscopic testing would be needed to identify the cause accurately. Foamy or frothy urine can sometimes be an indication of too much protein in the urine as well.
Specific Gravity: This test measures the overall concentration of all the chemicals that are dissolved in the urine and compares it to distilled water. Highly concentrated urine can indicate dehydration, but also can warn of kidneys with problems regulating the water content appropriately.
Chemical Analysis: Chemical tests get at the less visible, but often more important analysis of urine. Some of these involve simple dipstick methods, but others require sensitive laboratory equipment. They include:
pH: This measures how acidic or alkaline the urine is. Usually the pH of urine is between 4.5 (acidic) and 8 (basic or alkaline) with neutral at 7.0. pH is not diagnostic for lupus nephritis, but highly acidic urine may indicate conditions such as dehydration, uncontrolled diabetes and certain respiratory diseases. Urine that is excessively basic may indicate urinary tract infections, and some kidney or lung problems.
Protein: Healthy kidneys generally allow very little protein to pass from the blood to the urine. Proteinuria is the condition of abnormal levels of protein in the urine and can indicate damage or inflammation in the glomeruli or tubules of the kidney. Since albumin is the most common protein to pass into the urine, this condition is also called albuminuria. It is a very important diagnostic biomarker for lupus nephritis and used in many scoring systems that measure disease activity, such as the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). The testing for proteins has often required a patient to collect urine over a 24-hour period – which can be time consuming. An alternative test from a one-time urine sample measures the ratio of protein to creatinine.
Creatinine: Speaking of measuring creatinine, this is another important chemical that may indicate kidney damage. Creatinine is a metabolic byproduct produced by muscles from the breakdown creatine. It is filtered out of the bloodstream by healthy kidneys at relatively predictable rate. If there are problems with the kidneys, creatinine levels will rise in the blood and decrease in the urine. This test often requires a creatinine blood test as well.
Glucose: Glucose is the predominant form of sugar that is found in the blood, and there should be little to none in the urine. Glucose is present when the kidneys are stressed, damaged or diseased. This occurs with lupus nephritis or more commonly with severe diabetes. Urine glucose test strips are available for home use, but blood tests are far more accurate and are necessary for an accurate diagnosis.
Ketones: Ketones are the substances made from your body breaking down fat into energy. Usually your body breaks down carbohydrates in your diet to generate energy, but if your diet doesn’t contain enough carbs, or if your body is not metabolizing blood sugar properly (as with diabetes), then ketones are made. When large amounts of ketones are found in the urine (ketonuria), there could be many causes, even excessive exercise or vomiting due to stomach flu. So, testing for ketones does not stand alone as a diagnostic for lupus. Tests include dipsticks and lab analysis, but the urine may also have a particularly sweet or strong smell if concentrations of ketones are high enough. It turns out that the recent popularity of the keto (ketogenic) diet has made ketone testing of urine with dipsticks a booming industry.
Nitrites: Nitrites are produced when certain bacteria transform nitrates into nitrites. This should not normally be noticed in urine unless those bacteria are causing a urinary tract infection. This is not a diagnostic for lupus, but is an important test to run in most urinalysis.
Microscopic Analysis: This entails the careful use of a microscope to identify and count blood cells, bacteria, cell fragments and even crystals in the urine. The results can be actual numbers or descriptive using terms like “rare,” “few” or “many.”
Red Blood Cells: Blood in the urine is usually not normal, though very small amounts are okay. Inflammation, damage from kidney stones, or injury to the bladder, ureters, kidneys and urethra as well as damage due to lupus nephritis can all cause blood in the urine. If there are red blood cells in the urine, the condition is called hematuria. It is also possible for the urinalysis to pick up hemoglobin in chemical tests. One thing to note is that urine tests can be contaminated from other sources of blood such as menstruation or hemorrhoids. So, it is important to note any of these when giving a urine sample.
Leukocytes: “Leukocytes” is a fancy name for white blood cells and these can be found in blood as well as many other tissues in the body. They can be normally found in the urine, but a high number can be caused by inflammation or urinary tract infections.
Casts: These are tube-shaped formations made in the tubules of the kidneys from proteins or red and white blood cells that stick together. They can be caused by damage to the glomeruli or general inflammation in the kidneys.
Crystals: Certain crystals are normal in the urine, but others, especially those produced by amino acids may indicate liver disease.
Bacteria or Yeast: Urine is supposed to be relatively sterile. However, with renal damage or urinary tract infections, a measurable amount of bacteria or yeast may be seen. If an infection is the issue, the urine sample may require a culture to identify the exact cause.
In Conclusion
Lupus nephritis is one of the most important concerns when it comes to making accurate and timely diagnoses of possible autoimmune conditions. While relatively rare as a form of nephritis, it has serious ramifications if not identified early. The results from a urinalysis are never enough to make this diagnosis, and that diagnosis often happens before the kidney involvement is noticed. However, it is a such a common and relatively simple test to take and everyone should understand how it can lead to a greater understanding of your overall health.
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References
Cameron, J.S. (1990). Lupus nephritis. Journal of the American Society of Nephrology, 10(2) 413-424. Retrieved from https://jasn.asnjournals.org/content/10/2/413
Karkar, A., & Abdeirahman, M. (2010). Protein-to-creatinine ratio: A valid estimate and alternative to 24 hour proteinuria. Saudi Journal of Kidney Diseases and Transplantation, 21(5) 949-950.
Lundberg, J.O, Carlsson, S, Engstrand, L., Morcos, E., Wiklund, N.P., & Weitzberg, E. (1997). Urinary nitrite: More than a marker of infection. Urology, 50(2) 189-191.
Petri, M., & Stojan, G. (n.d.). Urinalysis. Retrieved from https://www.hopkinslupus.org/lupus-tests/screening-laboratory-tests/urinalysis/
Author: Liz Heintz
Updated by KFL Team (2020)
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