Limitations
IgG is not useful for diagnosing infection in infants <6 months of age, because they are usually the result of passive transfer from the mother.
Low levels of IgM antibodies may occasionally persist for >12 months postinfection. For the determination of seroconversion from nonreactive to reactive, two serum samples should be drawn 3–4 weeks apart, during the acute and convalescent stages of the infection. The acute-phase sample should be stored and tested in parallel with the convalescent sample.
CDC suggests equivocal or positive results should be retested using a different assay from another reference laboratory specializing in toxoplasmosis testing (IgG dye test, IgM ELISA, reflex to avidity, and/or other tests).
In a pregnant patient, if both IgG/IgM positive, an IgG avidity test should be performed. A high avidity result in 12–16 weeks of pregnancy essentially rules out an infection acquired during gestation.
A low IgG avidity result should not be interpreted as recent infection, because some individuals have persistent low IgG avidity for many months after infection.
Newborn infants suspected of congenital toxoplasmosis should be tested by both an IgM- and an IgA-capture EIA (CDC recommendation). Detection of
Toxoplasma
-specific IgA antibodies is more sensitive than IgM detection in congenitally infected babies.
TRICHOMONAS VAGINALIS
MOLECULAR DETECTION
See: Sexually Transmitted Infections, Molecular Diagnosis (
Chlamydia trachomatis
,
Neisseria gonorrhoeae
,
Trichomonas vaginalis
)
URINE CULTURE (ROUTINE)
Definition
Urine culture is used for the detection of UTI caused by common uropathogenic bacteria and yeast. The range of UTI syndromes is broad, including asymptomatic bacteriuria through pyelonephritis with systemic symptoms. Patients with uncomplicated UTIs often present with dysuria and frequency, whereas pyelonephritis may be associated with signs of sepsis, including fever, flank pain, and nausea. The risk of UTI, including complicated UTI, is increased in patients with urinary tract prosthetic materials, like stents, GU tract malformations, history of GU surgery, and medical conditions, such as pregnancy, neurologic disorders, and DM.
Special Collection and Transport Instructions
Acceptable specimens:
Clean-catch midstream urine, straight catheterization (“in and out”), newly placed indwelling catheters, and suprapubic aspirates are commonly submitted and should be associated with low contamination rates.
Urine collected from an indwelling catheter or from pediatric collection bags is frequently contaminated. Negative cultures may be helpful in ruling out UTI; positive cultures should be interpreted with caution. Urine for culture should never be taken from a collection bag attached to an indwelling catheter.
