10-20 μg/mL

Critical value: >20.0 μg/mL

Criterion: recovery within plus or minus 10% of initial value 
at theophylline levels of approximately 5 and 15 μg/mL.

Icterus: No significant interference from bilirubin up to an I index 
of 50 (approximate bilirubin concentration: 50 mg/dL).

Hemolysis: No significant interference from hemoglobin up to an H 
index of 1000 (approximate hemoglobin concentration: 1000 mg/dL).

Lipemia (Intralipid): No significant interference up to an L index of 
300 (approximate triglycerides concentration: 1000 mg/dL). There is 
poor correlation between turbidity and triglycerides concentration.

No significant interference from total protein up to 12 g/dL or 
rheumatoid factor up to 100 IU/mL.

Due to cross-reactivity to 1,3 dimethyluric acid, this assay should 
not be used to quantitate samples from uremic patients (1-2).

The incidence of patients with antibodies to E. coli beta-
galactosidase is extremely low. However, some samples containing such 
antibodies can result in artificially high theophylline results that 
do not fit the clinical profile.

As with any assay employing mouse antibodies, the possibility exists
for interference by human anti-mouse antibodies (HAMA) in the sample, 
which could cause falsely elevated results.

References:
(1) Breiner R, McComb, Lewis S and Wong SHY, Marzouk N and Kapke GF.
    Positive interference with immunoassay of theophylline in serum of
    uremics, letters to the editor. Clin Chem. 1985;31:1575-1577.

(2) Nelson KM, Mathews SE, Bowers LD. Theophylline concentrations may
    be falsely high in serum of uremic patients, letters to the
    editors. Clin Chem. 1983;29:2125-2126.