Clinical urine tests
White blood cells seen under a microscope from a urine sample.
|Other codes||LOINC Codes for Urinalysis panels|
Clinical urine tests are examinations of the physical and chemical properties of urine and its microscopic appearance to aid in medical diagnosis. The term urinalysis—a blend of the words urine and analysis—generally refers to the gross examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Gross examination targets parameters that can be measured with the naked eye (or other senses), including volume, color, transparency, odor, and specific gravity; urine test strips measure chemical properties such as pH, glucose concentration, and protein levels; and light microscopy is performed to identify elements such as cells, urinary casts, crystals, and organisms.:441 Other analyses routinely performed on urine samples include urine electrolyte levels, drug testing, pregnancy testing and microbiological culture.
Urinalysis involves assessment of the physical properties of urine, such as color and clarity; chemical analysis using a urine test strip; and microscopic examination.:441 Microscopic examination is not always included: it may be reserved for samples that have abnormal results on preliminary examinations, or performed at the healthcare provider's request. Test strips contain pads impregnated with chemical compounds that change color when they interact with specific elements in the urine; for example, nitrite, a compound produced by some bacteria that cause urinary tract infections, and leukocyte esterase, an enzyme found in white blood cells (WBCs) which acts as an indicator of the number of WBCs in the urine. The intensity of the color change correlates roughly with the concentration of each compound.:397–406
If microscopy is necessary, the urine is first centrifuged to concentrate the solid elements so that they can be viewed more easily. A drop of the concentrated sample is placed under a coverslip and examined, typically at 10x and 40x magnification.:414–5 If it is necessary to determine the exact number of cells or casts in the sample, it can be placed in a counting chamber called a hemocytometer.:461 Urine is traditionally examined by light microscopy, but some laboratories use phase-contrast microscopes, which improve the visualization of elements such as urinary casts and mucus.:414–5 There are also automated systems that use pattern recognition to identify microscopic elements in the urine.
Urine test strip
A urine test strip can quantify:
- Leukocytes – with presence in urine known as leukocyturia
- Nitrite – with presence in urine known as nitrituria
- Protein – with presence in urine known as proteinuria, albuminuria, or microalbuminuria
- Erythrocytes – with presence in urine known as hematuria
- Specific gravity
- Glucose - with presence in urine known as glucosuria
- Bilirubin - with presence in urine known as bilirubinuria
- Ketones - with presence in urine known as ketonuria
- Hematuria – associated with kidney stones, infections, tumors and other conditions
- Pyuria – associated with urinary infections
- Eosinophiluria – associated with allergic interstitial nephritis, atheroembolic disease
- Red blood cell casts – associated with glomerulonephritis, vasculitis, or malignant hypertension
- White blood cell casts – associated with acute interstitial nephritis, exudative glomerulonephritis, or severe pyelonephritis
- (Heme) granular casts – associated with acute tubular necrosis
- Crystalluria – associated with acute urate nephropathy (or acute uric acid nephropathy, AUAN)
- Calcium oxalatin – associated with ethylene glycol, kidney stone disease
- Waxy casts – associated with chronic renal disease
- Urine culture – a microbiological culture of urine samples, detecting bacteriuria, is indicated when a urinary tract infection is suspected.
- Ictotest – this test is used to detect the destruction of old red blood cells in the urine.
- Hemoglobin test – this tests for hemolysis in the blood vessels, a rupture in the capillaries of the glomerulus, or hemorrhage in the urinary system, which cause hemoglobin to appear in the urine.
Urine test results should always be interpreted using the reference range provided by the laboratory that performed the test, or using information provided by the test strip/device manufacturer.
The following are examples of some urine colors and their causes (not a complete listing).
- Nearly colorless: Excessive fluid intake for conditions; untreated diabetes mellitus, diabetes insipidus, and certain types of nephritis.
- Yellow: Distinctly yellow urine may indicate excessive riboflavin (vitamin B2) intake.
- Yellow-amber: Normal.
- Yellow-cloudy: excessive crystals (crystalluria) and/or excessive pus (pyuria).
- Orange: Insufficient fluid intake for conditions; intake of orange substances; intake of phenazopyridine for urinary symptoms.
- Red: Leakage of red blood cells or of hemoglobin from such cells; hemolysis; intake of red substances.
- Reddish-orange: Intake of certain medications or other substances.
- Rusty-yellow to reddish-brown: Intake of certain medications or other substances.
- Dark brown: Intake of certain medications or other substances; damaged muscle (myoglobinuria due to rhabdomyolysis) from extreme exercise or other widespread damage, possibly medication related; altered blood; bilirubinuria; intake of phenolic substances; inadequate porphyrin metabolism; melanin from melanocytic tumors; presence of an abnormal form of hemoglobin, methemoglobin.
- Brownish-black to black: Intake of substances or medications; altered blood; a problem with homogentisic acid metabolism (alkaptonuria), which can also cause dark whites of the eyes and dark-colored internal organs and tissues (ochronosis); Lysol (a product that contains phenols) poisoning; melanin from melanocytic tumors). Paraphenylenediamine is a highly toxic ingredient of hair dye formulations that can cause acute kidney injury and result in black urine.
- Purple due to Purple urine bag syndrome.
- Magenta to purple-red: Presence of phenolphthalein, a stimulant laxative previously found in Ex-Lax.
- Green, or dark with a greenish hue: Jaundice (bilirubinuria); problem with bile metabolism. Recent surgery requiring high doses of propofol infusion. The use of a medication (Uribel) that is similar to phenazopyridine for the relief of urinary symptoms.
- Other colors: Various substances ingested in food or drink, particularly up to 48 hours prior to the presence of colored urine.
The odor (scent) of urine can normally vary from odorless (when very light colored and dilute) to a much stronger odor when the subject is dehydrated and the urine is concentrated. Brief changes in odor are usually merely interesting and not medically significant. (Example: the abnormal smell many people can detect after eating asparagus.) The urine of diabetics experiencing ketoacidosis (urine containing high levels of ketone bodies) may have a fruity or sweet smell.
Ions and trace minerals
|Target||Lower limit||Upper limit||Unit||Comments||LOINC Codes|
|Nitrite||n/a||The presence of nitrites in urine, termed nitrituria, indicates the presence of coliform bacteria.|
|Sodium (Na) – per day||150||300||mmol / 24 h||A urinalysis is frequently ordered during the workup of acute kidney injury. Full kidney function can be detected through the simple dipstick method.||2956-1|
|Potassium (K) – per day||40||90||mmol / 24 h||Urine K may be ordered in the workup of hypokalemia. In case of gastrointestinal loss of K, the urine K will be low. In case of renal loss of K, the urine K levels will be high. Decreased levels of urine K are also seen in hypoaldosteronism and adrenal insufficiency.||2829-0|
|Urinary calcium (Ca) – per day||15||20||mmol / 24 h||An abnormally high level is called hypercalciuria and an abnormally low rate is called hypocalciuria.||14637-3|
|100||250||mg / 24 hours||6874-2|
|Phosphate (P) – per day||n/a||38||mmol / 24 h||Phosphaturia is the hyperexcretion of phosphate in the urine. This condition is divided into primary and secondary types. Primary hyperphosphaturia is characterized by direct excess excretion of phosphate by the kidneys, as from primary kidney dysfunction, and also the direct action of many classes of diuretics on the kidneys. Additionally, secondary causes, including both types of hyperparathyroidism, cause hyperexcretion of phosphate in the urine.||14881-7|
A sodium-related parameter is fractional sodium excretion, which is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is a useful parameter in acute kidney failure and oliguria, with a value below 1% indicating a prerenal disease and a value above 3% indicating acute tubular necrosis or other kidney damage.
Proteins and enzymes
|Target||Lower limit||Upper limit||Unit||Comments|
|mg/dl||Proteins may be measured with the Albustix test. Since proteins are very large molecules (macromolecules), they are not normally present in measurable amounts in the glomerular filtrate or in the urine. The detection of protein in urine, called proteinuria, may indicate the permeability of the glomerulus is increased. This may be caused by renal infections or by other diseases that have secondarily affected the kidneys, such as hypertension, diabetes mellitus, jaundice, or hyperthyroidism.|
|Human chorionic gonadotropin (hCG)||–||50||U/l||This hormone appears in the urine of pregnant women. It also appears in cases of testicular cancer in men. Home pregnancy tests commonly detect this substance.|
|Target||Lower limit||Upper limit||Unit||Comments|
|Red blood cells (RBCs) /
|0||2 – 3||per
High Power Field
|May be present as intact RBCs, which indicate bleeding. Even a trace amount of blood is enough to give the entire urine sample a red/pink hue, with difficulty in judging the amount of bleeding from a gross examination. Hematuria may be due to a generalized bleeding diathesis or a urinary tract-specific problem (trauma, stone...urolithiasis, infection, malignancy, etc.) or artifact of catheterization in case the sample is taken from a collection bag, in which case a fresh urine sample should be sent for a repeat test.
If the RBCs are of renal or glomerular origin (due to glomerulonephritis), the RBCs incur mechanical damage during the glomerular passage, and then osmotic damage along the tubules, so dysmorphic features appear. The dysmorphic RBCs in urine most characteristic of glomerular origin are called "G1 cells", doughnut-shaped rings with protruding round blebs sometimes looking like Mickey Mouse's head (with ears).
Painless hematuria of nonglomerular origin may be a sign of urinary tract malignancy, which may warrant a more thorough cytological investigation.
|RBC casts||n/a||0 / negative|
|White blood cells (WBCs) /
|0||2 / negative|
|–||10||per µl or
|"Significant pyuria" at greater than or equal to 10 leucocytes per microlitre (µl) or cubic millimeter (mm3)|
|n/a||0 / negative||dip-stick qualitative scale of 0 to 4+||Hemoglobinuria is suggestive of in vivo hemolysis, but must be distinguished from hematuria. In case of hemoglobinuria, a urine dipstick shows presence of blood, but no RBCs are seen on microscopic examination. If hematuria is followed by artefactual ex vivo or in vitro hemolysis in the collected urine, then the dipstick test also will be positive for hemoglobin and will be difficult to interpret. The urine color may also be red due to excretion of reddish pigments or drugs.|
|Target||Lower limit||Upper limit||Unit||Comments|
|Glucose||n/a||0 / negative||Glucose can be measured with Benedict's test. Although glucose is easily filtered in the glomerulus, it is not present in the urine because all of the glucose filtered is normally reabsorbed from the renal tubules back into the blood. Presence of glucose in the urine is called glucosuria.|
|Ketone bodies||n/a||0 / negative||With carbohydrate deprivation, such as starvation or high-protein diets, the body relies increasingly on the metabolism of fats for energy. This pattern is also seen in people with diabetes mellitus, when a lack of the hormone insulin prevents the body cells from using the large amounts of glucose available in the blood. This happens because insulin is necessary for the transport of glucose from the blood into the body cells. The metabolism of fat proceeds in a series of steps. First, triglycerides are hydrolyzed to fatty acids and glycerol. Second, the fatty acids are hydrolyzed into smaller intermediate compounds (acetoacetic acid, betahydroxybutyric acid, and acetone). Thirdly, the intermediate products are used in aerobic cellular respiration. When the production of the intermediate products of fatty acid metabolism (collectively known as ketone bodies) exceeds the ability of the body to metabolize these compounds, they accumulate in the blood and some end up in the urine (ketonuria).|
|Bilirubin||n/a||0 / negative||The fixed phagocytic cells of the spleen and bone marrow destroy old red blood cells and convert the heme groups of hemoglobin to the pigment bilirubin. The bilirubin is secreted into the blood and carried to the liver, where it is bonded to (conjugated with) glucuronic acid, a derivative of glucose. Some of the conjugated bilirubin is secreted into the blood and the rest is excreted in the bile as bile pigment that passes into the small intestine. The blood normally contains a small amount of free and conjugated bilirubin. An abnormally high level of blood bilirubin may result from an increased rate of red blood cell destruction, liver damage (as in hepatitis and cirrhosis), and obstruction of the common bile duct, as with gallstones. An increase in blood bilirubin results in jaundice, a condition characterized by a brownish-yellow pigmentation of the skin and of the sclera of the eyes.|
|Urobilinogen||0.2||1.0||Ehrlich units |
|Creatinine||4.8||19||mmol / 24 h|
|Urea||12||20||g / 24 h|
|Uric acid||250||750||mg / 24 h|
dopamine – per day
|90||420||μg / 24 hours|
|Free cortisol||28 or 30||280 or 490||nmol/24 h||Values below threshold indicate Addison's disease, while values above indicate Cushing's syndrome. A value smaller than 200 nmol/24 h (72 µg/24 h) strongly indicates absence of Cushing's syndrome.|
|10 or 11||100 or 176||µg/24 h|
|Phenylalanine||30.0||mg/L||In neonatal screening, a value above the upper limit defines phenylketonuria.|
Other urine parameters
|Test||Lower limit||Upper limit||Unit||Comments|
|Urine specific gravity||1.003||1.030||g/cc||This test detects the ion concentration of urine. Small amounts of protein or ketoacidosis tend to elevate the urine's specific gravity (SG). This value is measured using a urinometer and indicates hydration or dehydration. If the SG is under 1.010, the patient is hydrated; an SG value above 1.020 indicates dehydration.|
|Osmolality||400||n/a||mOsm/kg||Urine osmolality testing can be used in conjunction with Plasma osmolality tests to confirm diagnosis of SIADH|
|Bacterial cultures||by urination||–||100,000||colony forming units per millilitre (CFU/mL)||Bacteriuria can be confirmed if a single bacterial species is isolated in a concentration greater than 100,000 CFU/ml of urine in clean-catch midstream urine specimens (one for men, two consecutive specimens with the same bacterium for women).|
|by bladder catheterisation||–||100||For urine collected via bladder catheterisation, the threshold is 100 CFU/ml of a single species.|
Urine may be tested to determine whether an individual has engaged in recreational drug use. In this case, the urinalysis would be designed to detect whatever marker indicates drug use.
Helen Murray Free and her husband, Alfred Free, pioneered dry reagent urinalysis, resulting in the 1956 development of Clinistix (also known as Clinistrip), the first dip-and-read test for glucose in urine for patients with diabetes. This breakthrough led to additional dip-and-read tests for proteins and other substances. The invention was named a National Historic Chemical Landmark by the American Chemical Society in May 2010.
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