Becton Dickinson recently alerted us to the spuriously elevated hormone tests results obtained when samples collected in their serum separator tubes (SST) are measured by chemiluminescence technology (Immulite®). Antech Diagnostics uses primarily radioimmunoassays and has recently evaluated the effect of sample collection into SST on progesterone, thyroid, and cortisol concentrations, when measured by radioimmunoassay (RIA).

Progesterone concentrations measured by RIA may be falsely decreased in samples collected using SST. The sample of choice for progesterone concentrations is separated serum (from a sample collected originally into a plain red top tube).

There is no effect of sample collection into SST on thyroid or cortisol concentrations, when measured by RIA. SST or separated serum samples are appropriate for cortisol and thyroid testing by RIA.

Urinalysis should be performed on freshly collected urine for any animal with suspected urinary tract disease, and for routine health screening of geriatric pets. Cystocentesis is the preferred method of urine collection, whenever possible. Urine for culture should be submitted in a sterile red top tube (RTT), not a serum separator tube. Only a small volume of urine (~0.5 mL) is needed. A separate container of urine (at least 2 mL) should be submitted for routine urinalysis. Clients are encouraged to send a separate, sterile urine sample, along with each urinalysis, in case it is decided that an Add-On urine culture is needed. Copan swabs of urine or urine submitted in broth are not preferred forurine culture, and enable reporting only of semiquantitative culture results.

As a general rule, pets should be off antibiotics for at least 48-72 hours prior to urine culture. However, urine cultures performed during antibiotic treatment for UTI (without stopping antibiotics) can be used to assess treatment efficacy.