Improving Patient Adherence to Tuberculosis Treatment
Return to Table of Contents
Several simple, reliable, and relatively inexpensive tests for
demonstrating the presence in urine of TB drugs or their metabolites
have been developed. Methods for performing a variety of tests,
by Eidus and Ling, were published in a World Health Organization
technical bulletin in 1969. (1). More recently, others have published
the methods and results of testing urine for the presence of isoniazid
(INH) and its metabolites, pyrazinamide (PZA) and its metabolites,
rifampin and its metabolites, and ethambutol (EMB) (2-6).
A procedure for detecting the INH metabolite isonicotinic acid
in urine by using a reagent-impregnated paper test strip was described
by Kilburn et al (5). This dipstick test measures the presence of
the most widely used TB medication and can be conveniently incorporated
into TB patient care (see instructions at end of the appendix).
The Bacto INH test strips, for example, are available from Difco
Laboratories, in Detroit, Michigan. The Potts-Cozart method (6),
an alternative to the test strip method, is based upon a similar
chemical reaction, may be less expensive, and was used by the Arkansas
Department of Health.
Note: Caution is needed in the interpretation of results of urine
tests for drug metabolites. For example, the reliability of INH
test strips in clinical situations depends upon
1) the sensitivity and specificity of the strips in detecting the
presence of isonicotinic acid in urine, 2) the rate at which individual
patients metabolize INH, and 3) the timing of the test in relation
to the time when pills are ingested.
The INH test strips were shown to be 99% sensitive (very few false-negatives)
and 100% specific (no false-positives) for one
group of patients when urine was collected 20 to 24 hours after
pills were ingested, and it is believed that for most patients the
test is reliable when conducted at any time within 24 hours after
pills are ingested. However, the normal rate of INH metabolism
differs in various patient populations, and the average
time required for clearance of INH from the urine can be less than
In addition to normal differences between patients, which are constant
over time, temporary factors such as fluid intake, illness, or dehydration
may affect INH clearance and lead to false test results.
to Test Urine for INH and Its Metabolites by Using Bacto INH Test
- Store the test strips in the refrigerator at 20 to 80 C until
ready to use.
- Ask the patient to collect a urine specimen in a small container.
- Each paper test strip is enclosed in a small plastic tube. Take
one test strip enclosed in its sealed plastic tube from the jar.
Cut off one corner of the plastic tube at the arrow end of the
- At the opposite end of the strip from the arrow, squeeze about
1/2 inch of the plastic tube between thumb and forefinger (to
create a suction) and insert the cut end of the tube into the
urine specimen, below the surface.
- Release pressure between thumb and forefinger, drawing urine
into the plastic tube. Liquid should rise in the tube to cover
the arrow on the paper strip.
- The tube may now be left to float in the urine container or
may be transferred to a test tube.
- Keep the tube at room temperature and observe results in 15
to 30 minutes.
- Look for a blue, purple, or green color on the strip and in
the liquid in the tube. These colors are a positive test result,
indicating the presence of INH or its metabolites in the specimen.
If the reaction is weak, only the paper strip may appear colored.
Note: Use Bacto INH control disk each time a urine test is conducted.
(See instructions on the package of control disks for storage and
- Eidus L, Ling GM. Tests for the detection of antituberculosis
drugs or their metabolites in the urine. WHO Tech Bull 1969;76:1-9.
- Burkhardt KR, Nel EE. Monitoring regularity of drug intake in
tuberculosis patients by means of simple urine tests. S Afr Med
- Kirsten C, Armstrong C, Gatner EMS. A simple test for the identification
of ethambutol in urine. S Afr Med J 1980;58:992.
- Ellard GA, Grenfield C. A sensitive urine-test method for monitoring
the ingestion of isoniazid. J Clin Pathol 1977;30:84-7.
- Kilburn JO, Beam RE, David HL, Sanches E, Corpe RF, Dunn W.
Reagent-impregnated paper strip for detection of metabolic products
of isoniazid in urine. Am Rev Respir Dis 1972;106:923-4.
- Henderson WT. The development and use of the Potts-Cozart tube
test for the detection of isoniazid (INH) metabolites in urine.
J Ark Med Soc 1986; 82(10):445-6.
Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb
Please send comments/suggestions/requests
CDC/Division of Tuberculosis Elimination
Communications, Education, and Behavioral Studies Branch
1600 Clifton Rd., NE - Mailstop E-10, Atlanta, GA 30333