Urine pH
Urine pH testing is used to classify urine as either a dilute acid or base solution. Seven is the point of neutrality on the pH scale. The lower the pH, the greater the acidity of a solution; the higher the pH, the greater the alkalinity.
The glomerular filtrate of blood is usually acidified by the kidneys from a pH of approximately 7.4 to a pH of about 6 in the final urine(Webpath, 2021). Depending on the person's acid-base status, the pH of urine may range from 4.5 to 8. A urinary pH greater than 5.5 in the presence of systemic acidemia (serum pH less than 7.35) suggests renal dysfunction related to an inability to excrete hydrogen ions (Queremel Milani & Jialal, 2020).
The kidneys maintain normal acid-base balance primarily through the reabsorption of sodium and the tubular secretion of hydrogen and ammonium ions. Urine becomes increasingly acidic as the amount of sodium and excess acid retained by the body increases. Alkaline urine, usually containing bicarbonate-carbonic acid buffer, is normally excreted when there is an excess of base or alkali in the body. Secretion of an acid or alkaline urine by the kidneys is one of the most important mechanisms the body uses to maintain a constant body pH.
A highly acidic urine pH occurs in:
- Acidosis
- Uncontrolled diabetes
- Diarrhea
- Starvation and dehydration
- Respiratory diseases in which carbon dioxide retention occurs and acidosis develops
A highly alkaline urine occurs in:
- Urinary tract obstruction
- Pyloric obstruction
- Salicylate intoxication
- Renal tubular acidosis
- Chronic renal failure
- Respiratory diseases that involve hyperventilation (blowing off carbon dioxide and the development of alkalosis)
Typically, the pH of urine tends to be acidic. A diet rich in citrus fruits, legumes, and vegetables raises the pH and produces urine that is more alkaline. Most of the bacteria responsible for urinary tract infections make the urine more alkaline because the bacteria split urea into ammonia and other alkaline waste products. The urine pH varies in different types of acidosis and alkalosis. Control of pH is important in the management of several diseases, including bacteriuria, renal calculi, and drug therapy.
The formation of renal stones is related to the urine pH. Patients being treated for renal calculi are frequently given diets or medications to change the pH of the urine so that kidney stones will not form. Calcium phosphate, calcium carbonate, and magnesium phosphate stones develop in alkaline urine; when this occurs, the urine is kept acidic. Uric acid, cystine, and calcium oxalate stones precipitate in acidic urine; in this situation, the urine should be kept alkaline or less acidic than normal. Drugs such as streptomycin, neomycin, and kanamycin are effective in treating urinary tract infections if the urine is alkaline. During treatment with sulfa drugs, alkaline urine helps prevent formation of sulfonamide crystals.
Here are important points to remember about urinary pH:
Instant Feedback:
Most bacterial urinary tract infections cause the urine to become more alkaline.
Proteinuria/Albuminuria
Proteinuria refers to the presence of protein in the urine. In healthy persons, the urine contains no protein or only a trace amount of protein. Proteins in the urine are comprised of albumin and globulin from the plasma. Because albumin is filtered more easily than globulin, it is the predominant type of protein that may appear in the urine. The term albuminuria may be used interchangeably with proteinuria.
Detection of protein in the urine, combined with a microscopic exam of urinary sediment, provides the basis for the differential diagnosis of renal disease. Normally, the glomeruli prevent passage of protein from the blood to the glomerular filtrate. A small amount of filtered plasma proteins and proteins secreted by the nephrons can be found in normal urine; however, in healthy individuals, protein excretion does not exceed 150 mg in 24 hours or 10 mg per 100 ml of any single specimen. Glomerular injury causes increased permeability to plasma proteins, resulting in proteinuria. A persistent finding of proteinuria is the single most important indication of renal disease. If more than a trace of protein is found on a routine UA, a quantitative 24-hour evaluation of protein excretion is done.
The dipstick method of checking for protein does not detect the presence of abnormal proteins such as globulins and Bence-Jones proteins excreted in multiple myeloma. Persons with diabetes have a higher than normal potential for renal disease, so they may have regular checks for proteinuria. If random samples are persistently positive for protein, a quantitative (24-hour) sample may be done.
Proteinuria is described based on the following scale:
• Trace = less than 150 mg/24 hours (upper limit of normal)
• 1+ = 200 - 500 mg/24 hours
• 2+ = 500 - 1500 mg/24 hours
• 3+ = over 2500 mg/24 hours
• 4+ = over 3000 mg/24 hours
Microalbuminuria
Microalbuminuria is the presence of a slightly high level of protein in the urine, and macroalbuminuria is the presence of a very high level of albumin in the urine each day. Results of the microalbuminuria test are measured as milligrams (mg) of protein leakage in your urine over 24 hours. Results generally indicate the following:
- Less than 30 mg of protein is normal.
- Thirty to 300 mg of protein is known as microalbuminuria, and it may indicate early kidney disease.
- More than 300 mg of protein is known as macroalbuminuria, and it indicates more advanced kidney disease.
Microalbumin is screened annually to assess kidneys in patients with diabetes.
In patients with hypertension microalbumin may be used more frequently. High blood pressure can cause damage to the vessels of the kidney, resulting in the release of albumin into the urine.Microalbuminuria
Microalbuminuria is the presence of a slightly high level of protein in the urine, and macroalbuminuria is the presence of a very high level of albumin in the urine each day. Results of the microalbuminuria test are measured as milligrams (mg) of protein leakage in your urine over 24 hours. Results generally indicate the following:
- Less than 30 mg of protein is normal.
- Thirty to 300 mg of protein is known as microalbuminuria, and it may indicate early kidney disease.
- More than 300 mg of protein is known as macroalbuminuria, and it indicates more advanced kidney disease.
Microalbumin is screened annually to assess kidneys in patients with diabetes.
In patients with hypertension microalbumin may be used more frequently. High blood pressure can cause damage to the vessels of the kidney, resulting in the release of albumin into the urine
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Dipstick proteinuria indicates presence of albumin.
Specific gravity
Specific gravity measures the kidney's ability to concentrate or dilute urine in relation to plasma. Because urine is a solution of minerals, salts, and compounds dissolved in water, the specific gravity is greater than 1.000 (water). The more concentrated the urine, the higher the urine specific gravity. An adult's kidneys have a remarkable ability to concentrate or dilute urine. In infants, the range for specific gravity is less because immature kidneys are not able to concentrate urine as effectively as mature kidneys.
Glucose, protein, or dyes used in diagnostic tests excreted into the urine increase the specific gravity. If none of these abnormal substances are present in the urine, there are two primary reasons why the kidney is producing concentrated urine with a high specific gravity. The first and most common reason for an increase in urine specific gravity is dehydration. The second reason for a high specific gravity is an increased secretion of anti-diuretic hormone (ADH). ADH causes increased tubular water re-absorption and decreased urine volume. Trauma, stress reactions, surgery, and many drugs cause an increase in ADH secretion.
A low specific gravity occurs in three situations.
It is important for the nurse to be aware of the physiological dynamics of surgical diuresis. After a major surgical procedure that produces high physiologic and psychological stress, increased secretion of antidiuretic hormone causes fluid retention within the vascular space. As stress after surgery decreases, ADH and other hormones, such as glucocorticosteroids, begin to drop to normal values, and the fluid that was held in reserve is excreted. This increase in urine volume a few days after surgery is sometimes referred to as a surgical diuresis. It is important for nurses to consider this type of fluid retention and related increase in urine specific gravity in the immediate post-operative patient to avoid excessive fluid replacement.
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The expected response immediately after major surgery is fluid retention.
Glycosuria
Glycosuria refers to sugar in the urine. Less than 0.1% of glucose normally filtered by the glomeruli appears in the urine, and less than 130 mg should appear in the urine over a 24-hour period. Glucose is present in glomerular filtrate but is reabsorbed by the kidney's proximal tubule. If the blood glucose level exceeds capacity of the tubules to reabsorb, glucose present in the glomerular filtrate, spills into the urine.Glycosuria indicates the person is hyperglycemic or has a lowered renal threshold for glucose. The renal threshold for glucose is approximately 160 to 190mg/dl of blood; glucose does not appear in the urine until the blood glucose rises above this level.
Occasionally, glycosuria may be a normal finding, such as after eating a heavy meal or during times of emotional stress. Some individuals have a benign condition in which they have a lower than usual renal threshold for glucose, but have normal blood glucose levels. In pregnancy, the renal threshold for glucose may be lowered, and small amounts of glycosuria may be present. Patients on hyperalimentation may have glycosuria if the carbohydrate solution is being infused faster than the pancreas can produce insulin. The most common reason for glycosuria is diabetes mellitus. Urine glucose tests screen for diabetes, confirm a diagnosis of diabetes, or monitor diabetic control.
Ketonuria
Ketones are metabolic end products of fatty acid metabolism. In healthy individuals, ketones are formed in the liver and are completely metabolized so that only negligible amounts appear in the urine. However, when carbohydrates are unavailable or unable to be used as an energy source, fat becomes the predominant body fuel instead of carbohydrates and excessive amounts of ketones are formed as a metabolic byproduct. A finding of ketones in the urine indicates that the body is using fat as the major source of energy.
Three ketone bodies that appear in the urine when fats are burned for energy are acetone, acetoacetic acid and beta-hydroxybutyric acid. Normally, the urine should not contain enough ketones to give a positive reading. As with tests for glucose, acetone can be tested by a dipstick or by a tablet. The results are reported as small, moderate, or large amounts of acetone. A small amount of acetone is a value under 20mg/dl; a moderate amount is a value of 30-40mg/dl, and a finding of 80mg/dl or greater is reported as a large amount.
Screening for ketonuria is done frequently for acutely ill patients, presurgical patients, and pregnant women. Any diabetic patient who has elevated levels of blood and urine glucose should be tested for urinary ketones. . Diabetic patients who use oral hypoglycemic agents should have their urine tested regularly for glucose and ketones because oral hypoglycemic agents, In conditions associated with acidosis, urinary ketones are tested to assess the severity of acidosis and to monitor treatment response. Urine ketones appear before there is any significant increase in blood ketones; therefore, urine ketone measurement is especially helpful in emergency situations. During pregnancy, early detection of ketonuria is essential because ketoacidosis is a factor associated with intrauterine death.
Ketosis and ketonuria occur in:
In nondiabetic persons, ketonuria may occur during acute illness or severe stress. Approximately 15% of hospitalized patients may have ketonuria, even though they do not have diabetes. In a diabetic patient, ketone bodies in the urine suggest that the patient is not adequately controlled and that adjustments of medication, diet, or both should be made promptly. In the nondiabetic patient, ketonuria reflects a reduced carbohydrate metabolism and excessive fat metabolism.
Instant Feedback:
Diabetic patients switching from insulin to oral hypoglycemic agents should have urinary ketones checked to assess the effectiveness of therapy.
Urinary Nitrites and Leukocyte Esterase
Tests to detect nitrites and leukocyte esterase have become part of a routine urinalysis.
Nitrites
Some species of bacteria that colonize the urinary tract can convert urinary nitrate (NO3) into urinary nitrites (NO2). The majority of circulating nitrates are dietary derived nitrates absorbed in the stomach and intestine, and excreted by the kidneys (Ma L. 2018).
In healthy people, both the urinary nitrite test and the leukocyte esterase (LE) tests are negative. A negative nitrite test does not necessarily mean that the urine is free of all bacteria, particularly if there are clinical symptoms, because some bacteria do not produce nitrites. Optimal results for a urinary nitrite test are obtained by analyzing an early morning. specimen that has been incubating in the bladder for 4 hours or more. A clean catch or mid-stream specimen is important to reduce bacterial contamination.
Leukocyte esterase
White cells in the urine usually indicate a urinary tract infection. The leukocyte esterase (LE) test detects esterase, an enzyme released by white blood cells. Positive test results are clinically significant. The LE test is also used to screen for gonorrhea and for amniotic fluid infections. The combination of the LE test with the urinary nitrite test provides an excellent screen for predicting a urinary tract infection. A urine sample that tests positive for both nitrate and leukocyte esterase should be cultured for pathogenic bacteria.
These tests are indirect ways of detecting bacteria in the urine. Significant urinary tract infections may be present in patients who do not experience other symptoms. If undetected and untreated they can cause potentially severe kidney disease. The urinary nitrite and LE tests are often ordered to screen patients at high-risk for urinary tract infections, including pregnant women, school-age females, elderly patients, and persons with a history of urinary tract infections.
Instant Feedback:
The combination of the LE test with the urinary nitrite test provides an excellent screen for predicting a urinary tract infection.
Reference:
Ma, L., Hu, L., Feng, X., & Wang, S. (2018). Nitrate and Nitrite in Health and Disease. Aging and disease, 9(5), 938–945. https://doi.org/10.14336/AD.2017.1207
Queremel Milani, D. A., & Jialal, I. (2020). Urinalysis. PubMed; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557685/
Webpath 2021. Tutorials - Pathology Subjects. Urinalysis. Accessed 7/26/21 from
https://webpath.med.utah.edu/TUTORIAL/
URINE/URINE.html