Urine drug screening

Definition

Urine drug screening, or toxicological screening, is a process of chemical analysis designed to test patients for drug abuse, or to insure that a patient is substance-free before undergoing a medical procedure.

Description

Urine drug screening can be used to evaluate possible accidental or intentional overdose or poisoning, to assess the type and amount of prescribed and/or illicit drugs used by a person, or to determine the cause of acute drug toxicity. It is also used to monitor drug dependency or to determine the presence of drugs in the body for medical and legal purposes.

In many occupations, urine drug screening has become a required condition of employment. Nearly all workers in certain occupations, such as law enforcement and transportation, must submit to periodic, random, and post-incident drug screening. Federal laws mandate the administration of drug screens to workers in the transportation industry, including bus drivers, truckers, airline employees, and railroad workers. Federally required testing must be conducted by a laboratory certified by the Substance Abuse and Mental Health Services Administration. Other industries must follow state regulations, which vary considerably.

Urine screening tests are able to detect general classes of compounds, such as amphetamines , barbiturates , benzodiazepines, and opiates. Drug screening can also detect cocaine, marijuana, and phencyclidine (PCP). The screening tests themselves are unable to distinguish between illicit and prescription drugs within the same class. A patient taking prescribed codeine pills and an individual using heroin would both show positive urine screening tests for opiates. It is also possible for some over-the-counter medications to cause a positive drug screen in someone who has taken neither illegal nor prescription drugs. These incorrect reactions are known as "false-positives."

Urine drug screens can detect the use of several drugs. Some of these drugs are as follows:

• cocaine
• amphetamines
• heroin
• morphine
• phencyclidine (PCP)
• benzodiazepines
• alcohol
• hydromorphone
• tetrahydrocannabinol (THC)
• propoxyphene
• methadone
• codeine
• barbituates

Certain foods, such as poppy seeds, may result in a positive urine screen for opiates, since poppy seeds are derived from opium poppies. Preliminary urine screening results, when positive, should be confirmed by a more accurate method that can distinguish between poppy seed ingestion and use of heroin or other opiates. Poppy seeds and opiates produce different chemicals, known as metabolic breakdown products or metabolites, as they travel through the body, allowing them to be distinguished from one another.

Sample collection

The method of collecting a urine sample for drug screening can be important. Some illicit drug users may attempt to substitute another person's urine, or chemically alter their own specimen. If the urine drug screen is being used for an important decision, such as employment or legal action, procedures to minimize chances of an adulterated or substituted sample may be necessary. These include measuring the temperature or pH of the sample immediately after it is procured, and using tamper-proof containers. Supervised specimen collection may be conducted to ensure that the urine indeed comes from the person being screened.

The most commonly used method for urine drug screening is immunoassay, a rapid and accurate test that uses antibodies embedded on test strips to reveal drug use. Antibodies react only in the presence of very specific substances—in this case, drugs present in urine. When a sufficient concentration of a drug (or drugs) are present, the test strip will indicate which substances have been detected. A control band on each strip confirms that the test was done correctly.

Positive screening results should always be confirmed by a more sensitive method. The most widely accepted corroborative test for all drugs is gas chromatography/mass spectrometry (GC/MS), which can determine the specific substances in the body by recognizing not only the molecular structure of the original compound, but also its metabolite, a chemical created when the drug is metabolized.

See also Addiction; Amphetamines and related disorders; Anti-anxiety drugs and abuse-related disorders; Barbiturates; Cannabis and related disorders; Cocaine and related disorders; Disease concept of chemical dependency; Methadone; Opioids and related disorders; Sedatives and related disorders

Resources

BOOKS

Kaplan, Harold, MD, and Benjamin J. Sadock, MD. Synopsis of Psychiatry. 8th edition. Philadelphia: Lippincott Williams and Wilkins, 1998.

PERIODICALS

Persoon, Thomas, MS. "Virtual Hospital: Clinical Laboratory Improvement Act: Therapeutic Drug Monitoring and Drug Abuse Screening, IV." Screening for Drugs of Abuse. The University of Iowa, 1999.

Policy Statement: Drug and Alcohol Screening. American Academy of child and Adolescent Psychiatry, Approved by Council, October 1990.

Barbara S. Sternberg, Ph.D.

Cystometry

Definition

Cystometry is a test of bladder function in which pressure and volume of fluid in the bladder is measured during filling, storage, and voiding.

Purpose

The urinary bladder stores urine produced by the kidneys. The main muscle of the bladder wall, the detrusor, relaxes to allow expansion of the bladder during filling. The urethra, the tube through which urine exits, is held closed by a ring of muscle, known as the urethral sphincter. As volume increases, stretching of the detrusor and pressure on the sphincter sends signals to the brain, indicating the need for urination, or voiding. Voluntary relaxation of the sphincter and automatic contractions of the detrusor allow successful and virtually complete voiding.

A cystometry study is performed to diagnose problems with urination, including incontinence, urinary retention, and recurrent urinary tract infections. Urinary difficulties may occur because of weak or hyperactive sphincter or detrusor, or incoordination of their two activities. Infection of the bladder or urethra may cause incontinence, as can obstruction of the urethra from scar tissue, prostate enlargement, or other benign or cancerous growths. Loss of sensation due to nerve damage can lead to chronic overfilling.

Precautions

The mild irritation of the urinary tract necessary for insertion of the catheter may occasionally cause flushing, sweating, and nausea.

Description

The patient begins by emptying the bladder as much as possible. A thin plastic catheter is then slowly inserted into the urethra until it reaches the bladder. Measurements are taken of the residual urine volume and bladder pressure. Pressure measurements may require a rectal probe to account for the contribution of the abdominal muscles to the pressure recording.

The bladder is then gradually filled with either warm water, room temperature water, saline solution, carbon dioxide gas, or a contrast solution for x-ray analysis, depending on the type of study being done. The patient is asked to describe sensations during filling, including temperature sensations and when the first feeling of bladder fullness occurs. Once the bladder is completely full, the patient is asked to begin voiding, and measurements are again made of pressure and volume, as well as flow rate and pressure.

Preparation

There is no special preparation needed for this test. The patient may be asked to stop taking certain medications in advance of the test, including sedatives, cholinergics, and anticholinergics.

Aftercare

Cystometry can be somewhat uncomfortable. The patient may wish to reserve an hour or so afterward to recover. Urinary frequency or urgency, and some reddening of the urine, may last for a day. Increasing fluid intake helps to flush out the bladder, but caffeinated, carbonated, or alcoholic beverages are discouraged, because they may irritate the bladder lining. Signs of infection, such as fever, chills, low back pain, or persistent blood in the urine, should be reported to the examining physician.

Risks

There is a slight risk of infection due to tearing of the urethral lining.

Normal results

The normal bladder should not begin contractions during filling and should initially expand without resistance. A feeling of fullness occurs with a volume of 100-200 ml. The adult bladder capacity is 300-500 ml. The sphincter should relax and open when the patient wills it, accompanied by detrusor contractions. During voiding, detrusor contraction should be smooth and lead to a steady urine stream.

Abnormal results

Inability of the bladder to relax during filling, or low bladder volume, may indicate interstitial cystitis, prostate enlargement, or bladder cancer. Contraction of the bladder during filling may be due to irritation from infection or cysts, obstruction of the bladder outlet, or neurological disease such as stroke, multiple sclerosis, or spinal cord injury. Diminished sensation may occur with nerve lesions, peripheral neuropathy, or chronic overfilling.

Resources

OTHER

"Cystometrogram, Simple and Complex." HealthGatePage. 〈http://www.healthgate.com/HealthGate/free/dph/static/dph.0085.shtml〉.

KEY TERMS

Detrusor— Muscle of the bladder wall.

Sphincter— Ring of muscle between the bladder and the urethra that functions to close off the urethra.

Urethra— Tube that empties urine from the bladder to the exterior of the body.

Urine Culture

Definition

A urine culture is a diagnostic laboratory test performed to detect the presence of bacteria in the urine (bacteriuria).

Purpose

Culture of the urine is a method of diagnosis for urinary tract infection that determines the number of microorganisms present in a given quantity of urine.

Precautions

If delivery of the urine specimen to the laboratory within one hour of collection is not possible, it should be refrigerated. The health care provider should be informed of any antibiotics currently or recently taken.

Description

There are several different methods for collection of a urine sample. The most common is the midstream clean-catch technique. Hands should be washed before beginning. For females, the external genitalia (sex organs) are washed two or three times with a cleansing agent and rinsed with water. In males, the external head of the penis is similarly cleansed and rinsed. The patient is then instructed to begin to urinate, and the urine is collected midstream into a sterile container. In infants, a urinary collection bag (plastic bag with an adhesive seal on one end) is attached over the labia in girls or a boy's penis to collect the specimen.

Another method is the catheterized urine specimen in which a lubricated catheter (thin rubber tube) is inserted through the urethra (tube-like structure in which urine is expelled from the bladder) into the bladder. This avoids contamination from the urethra or external genitalia. If the patient already has a urinary catheter in place, a urine specimen may be collected by clamping the tubing below the collection port and using a sterile needle and syringe to obtain the urine sample; urine cannot be taken from the drainage bag, as it is not fresh and has had an opportunity to grow bacteria at room temperature. On rare occasions, the health care provider may collect a urine sample by inserting a needle directly into the bladder (suprapubic tap) and draining the urine; this method is used only when a sample is needed quickly.

Negative culture results showing no bacterial growth are available after 24 hours. Positive results require 24-72 hours to complete identification of the number and type of bacteria found.

Preparation

Drinking a glass of water 15-20 minutes before the test is helpful if there is no urge to urinate. There are no other special preparations or aftercare required for the test.

Risks

There are no risks associated with the culture test itself. If insertion of a urinary catheter (thin rubber tube) is required to obtain the urine, there is a slight risk of introducing infection from the catheter.

Normal results

No growth of bacteria is considered the normal result, and this indicates absence of infection.

Abnormal results

Abnormal results, or a positive test, where bacteria are found in the specimen, may indicate a urinary tract infection. Contamination of the specimen from hair, external genitalia, or the rectum may cause a false-positive result. Identification of the number and type of bacteria, with consideration of the method used in obtaining the specimen, is significant in diagnosis.

Escherichia coli causes approximately 80% of infections in patients without catheters, abnormalities of the urinary tract, or calculi (stones). Other bacteria that account for a smaller portion of uncomplicated infections include Proteus klebsiella and Enterobacter.

Resources

ORGANIZATIONS

American Foundation for Urologic Disease. 300 West Pratt St., Suite 401, Baltimore, MD 21201.

KEY TERMS

Bacteriuria— The presence of bacteria in the urine.

Urine Flow Test

Definition

A urine flow test evaluates the speed of urination, or amount voided per second, and the total time of urination.

Purpose

A urine flow test is utilized to determine bladder function abnormalities, including a narrowed or obstructed urethra (the outflow passage from the bladder) and a weakened bladder muscle (detrusor).

Description

During a urine flow test, the patient urinates into a uroflowmeter, a funnel-shaped device that reads, measures, and computes the rate and amount of urine flow. The test takes approximately 10 minutes.

Preparation

The patient is prohibited from urinating at least two hours before the procedure.

Normal results

Average urine flow rates vary depending on age and gender.

Abnormal results

A urine flow test can indicate problems in bladder function, such as an obstruction, that will need further tests to diagnose.

Resources

BOOKS

Walsh, Patrick C., et al., editors. Campbell's Urology. Philadelphia: W. B. Saunders Co., 1998.

KEY TERMS

Detrusor muscle— Bladder muscle.

Urethra— Passageway that carries urine from the bladder.

URINE DIPSTICK

A urine dipstick is a colorimetric chemical assay that can be used to determine the pH, specific gravity, protein, glucose, ketone, bilirubin, urobilinogen, blood, leukocyte, and nitrite levels of an individual's urine. It consists of a reagent stick-pad, which is immersed in a fresh urine specimen and then withdrawn. After predetermined times the colors of the reagent pad are compared to standardized reference charts.

The urine dipstick offers an inexpensive and fast method to perform screening urinalyses, which help in identifying the presence of various diseases or health problems. This test should be interpreted with caution, however, due to numerous limitations, including inaccurate results due to medications and collection techniques. Abnormal values need to be confirmed with more precise quantitative measurements.

Bijan Shekarriz

Marshall L. Stoller

(see also: Genitourinary Disease; Urinalysis )