Urinalysis

A complete urinalysis evaluates several different aspects of your urine through physical, chemical, and microscopic examination. In lupus treatment, a urinalysis is often used to monitor protein leakage and identify and assess urinary tract infections (UTIs). Most people with kidney lupus (lupus nephritis) will have an abnormal urinalysis. Protein, urine casts (especially red blood cell casts), red blood cells, or white blood cells in the urine can indicate serious kidney involvement; leukocyte esterase amy indicate a bladder infection.

Urine samples can be given at any time while at the doctor’s office. A urine culture is performed to assess for a bladder infection and to determine appropriate antibiotics. Before giving a urine sample, ask a medical professional to counsel you on how to prevent contamination. Several analytical elements of the complete urinalysis are explained below.

Physical Examination / Macroanalysis

In this portion of the analysis, the color, clarity, and concentration of the urine are evaluated. Abnormal colors can result from disease, certain foods, or contamination, so the physical examination is generally viewed as a crude assessment. Light or dark coloration also suggests how much water is being excreted. The clarity of urine is measured as either clear, slightly clear, cloudy, or turbid. Urine clarity, like urine color, suggests that substances may be present in the urine; for example, turbid urine suggests the presence of protein or excess cellular material. However, accurate conclusions regarding the origin of the urine clarity cannot be drawn until further chemical and microscopic tests are performed. The physical examination also includes specific gravity, which measures the concentration of the urine sample. Specific gravity compares the concentration of urine to that of water (1.000). Usually it is better for the urine given in a sample to be more concentrated; this allows the laboratory to more accurately detect substances being excreted by your body. If your urine is very dilute (i.e., you have been drinking lots of water or receiving fluid via IV), you may be asked to give another urine sample.

Chemical Analysis

The chemical examination measures several features of the urine. Most laboratories use chemical test strips (“dipsticks”) that change colors when dipped into the urine. Either the laboratory technician or an automated instrument will then read the reaction color for each test pad to determine the result for each test. The use of automated instruments helps to eliminate discrepancies that arise with human interpretation.

  • pH: Usually, the pH of urine is between 4.5 and 8.0. The kidneys regulate this acid-base chemistry by reabsorbing sodium and secreting hydrogen and ammonium ions. When the body retains excess sodium or acid, urine becomes more acidic (i.e., the pH is lower). Highly acidic urine can occur with uncontrolled diabetes, diarrhea, starvation, dehydration, and certain respiratory diseases. When your body retains excess base, your urine becomes more basic, or “alkaline” (i.e., the pH is higher). This can occur with urinary tract infections and certain kidney and lung conditions. Certain foods can also alter the pH of your urine. For example, eating excessive protein or cranberries can make your urine more acidic, whereas eating a low-carbohydrate or vegetarian diet can make your urine more basic. Sometimes people are asked by their doctors to regulate the pH of their urine through diet in order to manage certain diseases or medications. For example, kidney stones can occur if urine pH is too high or too low.
  • Protein: Excessive protein in the urine (proteinuria) is a sign of kidney involvement in lupus. Usually, your kidneys prevent protein from passing from your blood into your urine: loops of capillaries (glomeruli) that filter blood allow small particles to pass into the urine while retaining larger particles, such as protein, and kidney tubules reabsorb the smaller proteins that were able to escape. Large amounts of protein in the urine suggest that these glomeruli and tubules are inflamed or damaged in some way.
  • If there is a large amount of protein in the urine, your doctor may request that you give a 24-hour urine sample or obtain a random protein to creatinine ratio. These two tests are used to monitor lupus affecting the kidneys (lupus nephritis).
  • Glucose: Your urine should not contain glucose. If it does, your doctor will order further bloodwork and urine tests to determine the cause. Glucose in the urine is called glucosuria; it can occur in people with diabetes that is not properly regulated with insulin, in people with kidney problems that affect the absorption of glucose, in pregnant women, and in people with liver abnormalities or hormonal disorders.
  • Ketones: Ketones in the urine (ketonuria) indicate that your body is metabolizing its fat reserves instead of carbohydrates to obtain energy. This can occur in people on low-carbohydrate diets, people who are malnourished, or people who have a problem properly metabolizing carbohydrates (e.g., people with diabetes).  It can also occur with excessive exercise, loss of carbohydrates due to vomiting, or exposure to cold. In people with diabetes, ketonuria may indicate insufficient management with insulin.
  • Blood: The chemical examination of urine also measures the amount of red blood cells in the urine sample. The presence of red blood cells in the urine is known as hematuria, and the presence of hemoglobin (from red blood cells) is known as hemoglobinuria. Usually people have very small amounts of red blood cells in their urine, but even a minute increase can indicate a problem, such as a disease of the kidney or urinary tract, trauma, medications, smoking, or intense exercise (e.g., running a marathon). When the chemical test for blood in the urine is negative but the microscopic assessment shows the presence of red blood cells, the laboratory will usually check for the presence of vitamin C, which can interfere with test results. [It is important to also note that contamination of the urine sample with menstrual blood or hemorrhoids cannot be distinguished from the presence of red blood cells in the sample. Therefore, it is very important to tell your physician if you are menstruating or are experiencing any other condition that could contaminate your urine sample. It is also very important that you speak to your lab technician about proper aseptic technique when giving a urine sample.]
  • Leukocyte Esterase: Leukocyte esterase is an enzyme present in your white blood cells. Therefore, the presence of this substance in the urine indicates the presence of white blood cells (leukocyturia). White blood cells in the urine may indicate inflammation of the kidneys or urinary tract due to bacterial infection. It is important to note, however, that contamination of the urine can also cause the presence of white blood cells in the urine, so remember to practice proper aseptic technique when giving the sample.
  • Nitrite: Bacteria can convert nitrate to nitrite; therefore, the presence of nitrite in the urine usually indicates a bacterial infection (i.e., a urinary tract infection). However, not all bacteria can convert nitrate to nitrite, so it is possible to have a urinary tract infection while also having a negative nitrite test.
  • Bilirubin: Bilirubin is made by the liver from old red blood cells; it is then processed by the intestine and excreted from the body. Therefore, healthy individuals do not have bilirubin in their urine. The presence of bilirubin in the urine indicates that the liver is allowing the substance to leak back into the blood. This can be an early indication of liver disease, even when other symptoms, such as jaundice, are not present.

Microscopic Analysis

The microscopic examination uses a microscope to identify and count cells, crystals, bacteria, mucous, and other substances that may be present in the urine. The amount of a substance present is reported one of two ways: as a count with the microscope strength used to view the substance [“per low power field” (LPF) or “per high power field” (HPF)], or as an approximate amount (“rare,” “few,” “moderate,” or “many”).

  • Red Blood Cells: The microscopic examination looks at how many red blood cells are present per HPF. As discussed above, the presence of red blood cells in the urine can indicate a problem, such as a disease of the kidney or urinary tract, trauma, medications, smoking, or intense exercise (e.g., running a marathon). However, contamination of the urine sample with menstrual blood or hemorrhoids cannot be distinguished from the presence of red blood cells in the sample. Therefore, it is very important to tell your physician if you are menstruating or are experiencing any other condition that could contamination your urine sample. It is also very important that you speak to your lab technician about proper aseptic technique when giving a urine sample.
  • White Blood Cells: A high number of white blood cells in the urine indicates inflammation of the kidneys or urinary tract. Like the test for red blood cells, this test can be misread if the sample is contaminated; in this instance, contamination can occur from vaginal secretions, which are high in white blood cells. Therefore it is important that you speak to your lab technician about proper aseptic technique before giving a urine sample.
  • Epithelial Cells: The tissue that lines the surfaces of cavities and structures in your body is called epithelial tissue. In healthy individuals, epithelial cells from the bladder and external urethra are normally present in the urine in small amounts.  However, the amount of epithelial cells in the urine increases when someone has a urinary tract infection or some other cause of inflammation. Your doctor will evaluate the source of the problem by evaluating the type of epithelial cells that are present. For example, the presence of renal tubular epithelial cells (from your kidneys) may indicate kidney involvement. The presence of squamous epithelial cells may indicate contamination of the urine specimen.
  • Casts: Casts are formed in the tubules of they kidney when the tubules secrete a protein called Tamm-Horsfall protein. The origin of the casts causes them to take on a tubular or hotdog-like shape. These casts are known as hyaline casts and can be present in normal adults on the order of 0-5 per LPF. Strenuous exercise can cause more hyaline casts to be present.  However, casts made from red or white blood cells indicate problems in the kidney.  Red blood cells that stick together and form red blood cell casts usually indicate problems with the glomeruli, tiny ball-shaped structures in your kidneys that help filter blood and prevent the loss of valuable substances, such as blood cells and proteins. White blood cells casts indicate inflammation in the kidney. Cellular casts that remain in the nephron of your kidney for a long time before they are flushed out become granular casts and eventually waxy casts.
  • Bacteria: Bacteria in your urine can suggest infection, especially if you have other suggestive symptoms. If your doctor suspects that you may have a urinary tract infection, she/he will most likely order a culture or count of the bacteria. However, bacteria on the skin can also contaminate the urine sample and skew the results, so it is very important that you understand proper aseptic technique when giving a urine sample.
  • Crystals: Crystals can be present in the urine of healthy individuals; these crystals form when the pH, solute concentration, and temperature of your urine are within a specific range. If these crystals are made of substances that are supposed to be in urine, such as calcium oxalate or phosphate, then they are considered to be normal. Crystals made of substances that are not usually present in urine, such as cystine, tyrosine, or leucine (amino acids), are uncommon and usually indicate liver disease or some other abnormal process.

Sources

  • “Urinalysis.” Lab Tests Online. 8 April 2009. American Association for Clinical Chemistry. 12 July 2009. <http://labtestsonline.org/understanding/analytes/urinalysis/sample.html>.