False-positive tests

Lohmoller G, Matuschke A et al (1989) [False-positive test of autonomic neuropathy in HIV infection and AIDS Case control study of heart rate variability in 62 HIV positive patients]. Med Klin (Munich) 84(5) 242-245... 

Connaghan D. G Francis C. E., Ryan D. H., Marder V. J. Prevalence and clinical implications of heparin-associated false positive tests for serum fibrin(ogen) degradation products. Am J Clin Pathol 1986 86,304-10. 

Drug/Lab test interactions Captopril may cause a false-positive test for urine acetone. 

Oxaprozin- False-positive urine immunoassay screening tests for benzodiazepines have been reported in patients taking oxaprozin. False-positive test results may be expected for several days following discontinuation of oxaprozin therapy. 

Drug/Lab test interactions False-positive tests for urobilinogen may occur during nizatidine therapy. False-positive tests for urine protein with Multistix may occur during ranitidine therapy testing with sulfosalicylic acid is recommended. 

Cannabinoid test interaction - False-positive urine cannabinoid test results have been reported in uninfected volunteers who received efavirenz. False-positive test results... 

Prior to isolation and purification of analytes from hair, samples must be washed to remove externally applied drug, "dirt," and oils from the exterior of the hair to produce clean extracts and prevent false positive test results. Hair may be externally contaminated with drug following environmental exposure to drug through vapor or from contact with contaminated material such as hands, money, and clothing. 

A single dose of G-CSF in a healthy donor produced a false positive test for hepatitis B surface antigen using an enzyme immunoassay (95). 

Urinalysis after intravenous urography can give misleading results. Increased specific gravity, false positive tests for protein (with the sulfosalicylic acid and nitric acid ring methods, but not the bromophenyl dye test), and the presence of needle-like crystals have been reported. Pseudo-albuminuria can occur with a false-positive sulfosalicylic acid test (319). 

Treatment with levodopa results in false-positive tests for urinary glucose (66). 

Rifampicin metabolites in nrine can canse a false positive test for melanin when assessed with the von Jaksch test (134). 

A different form of verification bias can happen if more than one reference standard is used, and the two reference standards correspond to different manifestations of disease. This study design can produce differential verification bias. Suppose test-positive patients are verified with further testmg and test-negative patients are verified by clinical follow-up. An example is the verification of suspected appendicitis, with histopathology of the appendix versus natural history as the two forms of the reference standard. A patient is classified as having a false-positive test result if the... 

In relation to immunoassays, interference from proteins (usually antibodies) should be recognized. Ismail et aft found in a survey comprising more than 5000 TSH results that interference occurred in 0.5% of the samples, leading to incorrect results that in a majority of the cases could have changed the treatment. Rotmensch and Cole" described 12 patients in whom a diagnosis of postgestational choriocarcinoma was made based on false-positive test results for... 

Indication The test is used to discriminate patients with pheochromocytomas from patients with false-positive test. results for catecholamines or metabolites in either plasma or urine. 

Eisenhofer G, Goldstein DS, Walther MM, Friberg P, Lenders JW, Reiser HR, Pacak R. Biochemical diagnosis of pheochromocytoma How to distinguish true-from false-positive test results, J Clin Endocrinol Metab 2003 88 2656-66. 

Several biochemical tests have been developed for screening mine for the presence of bacteria. A common dipstick test detects the presence of nitrite in the urine, which is formed by bacteria that rednce nitrate normally present in the urine. False-positive tests are nncommon. False-negative tests are more common and freqnently are cansed by the presence of gram-positive organisms or P. aeruginosa that do not reduce nitrate. Other causes of false tests include low urinary pEf, frequent voiding, and dilute urine. 

Set up a hot water bath by half-filling a 250-mL beaker with distilled water and placing it on a hot plate so that the water becomes very hot before performing this test. Place five drops of the solution labeled P04 in a test tube and add two drops of concentrated HN03. Shake. Add five drops of ammonium molybdate solution, shake, and place in the hot water bath for 5 minutes. The formation of a yellow color or yellow precipitate is the positive test for phosphate. Bear in mind that contamination with residue from phosphate-containing soap may give a false-positive test for the unknowns. 

Severe inflammation, excess amount of bacteria, crystal-luria, hematuria, poor preservation of cells, and poor cellularity (<50 cells) are some of the causes of test failure. Prior radiation therapy in patients with a history of prostate cancer, endometrial cancer, or local/systemic chemotherapy can cause persistent chromosomal aberrations that can lead to erroneous false-positive test results. One should exercise caution to obtain a proper history. Seminal vesicle cells can look highly atypical or aneuploid, which can also lead to similar false-positive results. Presence of the characteristic golden yellow pigment in the cytoplasm serves as a clue for identifying these cells. 

Spatula - never place the spatula in the test solution, it may lead to false positive tests for iron and chromium. 

False positive results are possible with a luminol test. A false positive test is a test in which the results seem to indicate the presence of blood even if it is not actually there. Some metals, plants, paints, cleaning materials, and other... 

Carbamazepine can produce a false-positive test for tricyclic antidepressants on drug screening. 

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