Clinical urine tests

Urinalysis

White blood cells seen under a microscope from a urine sample.
Specialty clinical pathology
MeSH D016482
Other codes LOINC Codes for Urinalysis panels
MedlinePlus 003579

Clinical urine tests are various tests of urine for diagnostic purposes. The most common is a urinalysis (UA), one of the most common methods of medical diagnosis.[1] The word is a portmanteau of the words urine and analysis.[2] Other tests are urine culture (a microbiological culture of urine) and urine electrolyte levels.

The target parameters that can be measured or quantified in urinalysis include naked-eye (gross) examination for color and smell plus analysis for many substances and cells, as well as other properties, such as specific gravity.

A part of a urinalysis can be performed by using urine test strips, in which the test results can be read as color changes. Another method is light microscopy of urine samples.

Target parameters

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.[3]

In addition to the substances mentioned in tables below, other tests include a description of color and appearance.

Color

The following are examples of color change causes and not a complete listing.

Smell

The odor (scent) of urine can normally vary from odorless (when very light colored and dilute) to a much stronger odor when the person 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 contains high levels of ketone bodies) also may also have an abnormal odor.[6]

Ions and trace metals

Target Lower limit Upper limit Unit Comments LOINC Codes
Nitrite n/a 0 / negative[7] The presence of nitrites in urine, termed nitrituria, indicates the presence of coliform bacteria.

5802-4
Sodium (Na) – per day 150[8] 300[8] mmol / 24 h A urinalysis is frequently ordered during the workup of acute renal failure. Full kidney function can be detected through the simple dipstick method. 2956-1
Potassium (K) – per day 40[8] 90[8] 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[9] 20[9] mmol / 24 h An abnormally high level is called hypercalciuria and an abnormally low rate is called hypocalciuria.

 14637-3
100[9] 250[9] mg / 24 hours 6874-2
Phosphate (P) – per day n/a[8] 38[8] mmol / 24 h Phosphaturia is the hyperexcretion of phosphate in the urine. This condition is divided into primary and secondary types. Primary hypophosphaturia is characterized by direct excess excretion of phosphate by the kidneys, as from primary renal 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 renal failure and oliguria, with a value below 1% indicating a prerenal disease and a value above 3%[10] indicating acute tubular necrosis or other kidney damage.

Proteins and enzymes

Target Lower limit Upper limit Unit Comments
Protein 0 trace amounts[7]
/ 20 		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[11] U/l This hormone appears in the urine of pregnant women.And also in case of testicular cancer in male. Home pregnancy tests commonly detect this substance.

Blood cells

Target Lower limit Upper limit Unit Comments
Red blood cells (RBCs) /
erythrocytes		 0[7][12] 2[7] – 3[12] per
High Power Field
(HPF)		 May be present as intact RBCs, which indicate bleeding. Even trace amount of blood is enough to give the entire urine sample a red/pink hue, and it is difficult to judge 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, infection, malignancy, etc.) or artefact 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 get dysmorphic features. The dysmorphic RBCs in urine which are most characteristic of glomerular origin are called "G1 cells", which are 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[7]
White blood cells (WBCs) /
leukocytes /
(pus cells)		 0[7] 2[7] / negative[7]
– 10 per µl or
mm3		 "Significant pyuria" at greater than or equal to 10 leucocytes per microlitre (µl) or cubic millimeter (mm3)
"Blood" /
(actually hemoglobin) 		n/a 0 / negative[7] 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.

Other molecules

Target Lower limit Upper limit Unit Comments
Glucose n/a 0 / negative[7] 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[7] 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[7] 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[7] 1.0 [7] Ehrlich units
or mg/dL
Creatinine 4.8[8] 19[8] mmol / 24 h
Urea 12 20 g / 24 h
Uric acid 250 750 mg / 24 h
Free catecholamines,
dopamine – per day		 90 [13] 420 [13] μg / 24 hours
Free cortisol 28[14] or 30[15] 280[14] or 490[15] 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[16]) strongly indicates absence of Cushing's syndrome.[15]
10[17] or 11[16] 100[17] or 176[16] µg/24 h
Phenylalanine 30.0 mg/L[18] In neonatal screening, a value above the upper limit defines phenylketonuria.[18]

Other urine parameters

Test Lower limit Upper limit Unit Comments
Urine specific gravity 1.003 [1][7] 1.030[1][7] 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[8] n/a[8] mOsm/kg Urine osmolality testing can be used in conjunction with Plasma osmolality tests to confirm diagnosis of SIADH[19]
pH 5[7] 7[7] (unitless)
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.

Drugs

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.

History

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.[20] This breakthrough led to additional dip-and-read tests for proteins and other substances.[21] The invention was named a National Historic Chemical Landmark by the American Chemical Society in May 2010. [22]

Methods

When doctors suggest/prescribe a urinalysis, they will request either a routine urinalysis or a routine and microscopy (R&M) urinalysis, with the difference being a routine urinalysis does not include microscopy or culture.

Urine test strip

A urine test strip can quantify:

Microscopic examination

A urine sample is about to be examined under a phase-contrast microscope using a Neubauer counting chamber. The urine is under the cover slide, in the upper segment formed by the H-shaped grooves.

The numbers and types of cells and/or material such as urinary casts can yield a great detail of information and may suggest a specific diagnosis.

Other methods

See also

References

  1. 1 2 3 Simerville JA, Maxted WC, Pahira JJ (March 2005). "Urinalysis: a comprehensive review". American Family Physician. 71 (6): 1153–62. PMID 15791892.
  2. ↑ Harper, Douglas. "Urinalysis". Online Etymology Dictionary. Retrieved 26 September 2011.
  3. ↑ "Reference Ranges and What They Mean". Lab Tests Online (USA). Retrieved 22 June 2013.
  4. ↑ http://jama.jamanetwork.com/article.aspx?articleid=183837
  5. ↑ http://www.mayoclinic.org/diseases-conditions/urine-color/basics/causes/con-20032831
  6. ↑ http://www.mayoclinic.org/symptoms/urine-odor/basics/causes/sym-20050704
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Normal Reference Range Table Archived December 25, 2011, at the Wayback Machine. from The University of Texas Southwestern Medical Center at Dallas. Used in Interactive Case Study Companion to Pathologic basis of disease.
  8. 1 2 3 4 5 6 7 8 9 10 Reference range list from Uppsala University Hospital ("Laborationslista"). Artnr 40284 Sj74a. Issued on April 22, 2008
  9. 1 2 3 4 medscape.com - Urine Calcium: Laboratory Measurement and Clinical Utility By Kevin F. Foley, PhD, DABCC; Lorenzo Boccuzzi, DO. Posted: 12/26/2010; Laboratory Medicine. 2010;41(11):683–686. © 2010 American Society for Clinical Pathology. In turn citing:
    • Wu HBA. Tietz Guide to Clinical Laboratory Tests. 4th ed. St. Louis, MO: Saunders, Elsevier; 2006.
  10. ↑ "MedlinePlus Medical Encyclopedia: Fractional excretion of sodium". Retrieved 2009-05-02.
  11. ↑ Ajubi NE, Nijholt N, Wolthuis A (2005). "Quantitative automated human chorionic gonadotropin measurement in urine using the Modular Analytics E170 module (Roche)". Clinical Chemistry and Laboratory Medicine. 43 (1): 68–70. PMID 15653445. doi:10.1515/CCLM.2005.010.
  12. 1 2 "medical.history.interview: Lab Values". Retrieved 2008-10-21.
  13. 1 2 "University of Colorado Laboratory Reference Ranges". Retrieved 2008-10-21.
  14. 1 2 Converted from µg/24 h, using molar mass of 362.460 g/mol
  15. 1 2 3 Görges R, Knappe G, Gerl H, Ventz M, Stahl F (1999). "Diagnosis of Cushing's syndrome: Re-evaluation of midnight plasma cortisol vs urinary free cortisol and low-dose dexamethasone suppression test in a large patient group". Journal of endocrinological investigation. 22 (4): 241–249. PMID 10342356. doi:10.1007/bf03343551.
  16. 1 2 3 Converted from nmol/24h, using molar mass of 362.460 g/mol
  17. 1 2 MedlinePlus - Cortisol – urine. Update Date: 11/23/2009. Updated by: Ari S. Eckman. Also reviewed by David Zieve.
  18. 1 2 Kim NH, Jeong JS, Kwon HJ, Lee YM, Yoon HR, Lee KR, Hong SP (2010). "Simultaneous diagnostic method for phenylketonuria and galactosemia from dried blood spots using high-performance liquid chromatography-pulsed amperometric detection". Journal of Chromatography B. 878 (21): 1860–1864. PMID 20494631. doi:10.1016/j.jchromb.2010.04.038.
  19. ↑ William C. Wilson; Christopher M. Grande; David B. Hoyt (2007-02-05). Trauma: Critical Care. CRC Press. pp. 179–. ISBN 978-1-4200-1684-0.
  20. ↑ "Helen M. Free". American Chemical Society. Retrieved 13 November 2016.
  21. ↑ "The Development of Diagnostic Test Strips" (PDF). American Chemical Society. Retrieved 13 November 2016.
  22. ↑ "Al and Helen Free and the development of diagnostic test strips". American Chemical Society. Retrieved 13 November 2016.
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