Transporting fluids, blood cultures, and more
Delivering the goods to microbiology labs
Transporting specimens not collected on swabs-body fluids, blood cultures, respiratory specimens, urines, and stools-raises its own set of issues, said Susan E. Sharp, PhD, director of microbiology at Kaiser Permanente Northwest’s Regional Laboratory, Portland, Ore., a panelist at the ASM symposium on microbial specimen transport.
With body fluids such as synovial fluids, CAPD, pleural fluids, and pericardial fluids, the question with transport comes up primarily with blood culture bottles. "Should we put fluids in them? And if the answer is yes, should we do the inoculation at the bedside or should we do the inoculation after the specimen is delivered to the laboratory?"
The standard in clinical microbiology is that all body fluids can be inoculated directly into blood culture bottles either at the bedside or once the specimen reaches the laboratory. Studies that have looked at body fluids have found recovery of organisms to be better when they are inoculated into culture bottles, but they differ on whether bedside inoculation is superior to laboratory inoculation of blood culture bottles.
With blood cultures, the primary question is pre-incubation. "Should we, or shouldn’t we? And if we do, should we hold bottles at room temperature or incubate them before sending to the laboratory to be loaded onto a blood culture instrument?"
Manufacturers’ recommendations depend on how long a delay there will be before the blood culture bottles get onto an instrument. But independent studies have drawn slightly different conclusions from those of the manufacturers. For example, a 1996 study looked at incubation at 35°C, and holding at room temperature before loading Bactec 9240 bottles onto the instrument. It concluded that less-than-24-hour delay specimens should incubate at 35°C; if greater than 24 hours of delay, they should be held at room temperature (Chapin K, Lauderdale TL. J Clin Microbiol. 1996;34:543-549).
With respiratory specimens, the questions are what the best storage conditions are and whether specimens should be placed on swabs. A study on temporary storage of sputa and urines conducted at Research Medical Center, Kansas City, Mo., where Dr. Sharp worked previously, cultured 20 patient samples upon arrival in the microbiology laboratory, then split them into two sets, one held at room temperature and one at 4°C, culturing them at intervals thereafter-four, eight, 12, 24, 48, 72, and up to 96 hours later.
"Over the entire time frame, of those specimens held at room temperature, 70 percent showed significant change in culture results. We would expect that-that’s why we usually put our sputum specimens in the refrigerator. However, the sputum samples that were stored at 4°C overall still showed a significant culture result change of 30 percent."
"This was a very controlled experiment," she said, "because we know we put them in the refrigerator and they stayed there. And still we saw a 30 percent change throughout the time period we were looking at. And you know when they’re in somebody’s car being transported, it’s not controlled like this-so the results could potentially be worse."
Little information is available about putting sputum samples on swabs, she said. "We took 10 sputum samples that came to the laboratory, cultured them routinely, then put them on numerous swabs. One set of sputum swabs was held at room temperature and the other set was held at 4°C. One swab from each storage temperature was then cultured at the same time frames for up to 96 hours."
"Interestingly, if you look at these samples, at room temperature storage, one specimen lost its Hemophilus in only four hours. That same Hemophilus was lost at 4°C, but not until the 48-hour sampling. It was there up until that time."
"So from this limited study, storage of sputum specimens on swabs at 4°C seems to work. If these data would hold for larger numbers, we could conclude that if you process sputum samples submitted on swabs within 12 hours, there should be no more than a 10 percent difference between the sputum samples on a swab and the ones in a cup."
For urine samples, the questions are preservative or no preservative and whether specimens should be kept at room or refrigerator temperature. One study found that boric acid was unacceptable as a preservative and that nonpreserved urine samples should be delivered to the laboratory and processed promptly upon arrival.
After conducting a study of several urine samples at the laboratory at Research Medical Center, Dr. Sharp concluded that urine samples should be stored either with or without preservative at 4°C, and processed within 12 hours of collection to hold to between five and 10 percent significant culture change results.
Enteric transport media are widely used for preserving stool specimens while in transit from clinics or hospitals to the laboratory. But is one better than another? Fecal suspensions seeded with Salmonella and Campylobacter have shown different results, Dr. Sharp noted. "Salmonella looks to be pretty hearty. Salmonella was isolated for up to three weeks regardless of transport media used or if ordinary saline was used as the transport media. With Campylobacter, all transport media maintained viable organisms for the first 72 hours. However, after 72 hours of storage, four out of the six transport media evaluated failed to maintain viable organisms, to where, at 96 hours, we could no longer detect the Campylobacter organisms on subculture. With saline held at 4°C, however, we were still isolating Campylobacter three weeks later."
In summary, she said, blood culture bottles have been shown to do a good job with all body fluids, with bedside and laboratory inoculation apparently equal, assuming there’s not a huge delay in getting the specimen to the lab. "With blood cultures, you should follow the manufacturer recommendation or the recommendation of specific studies using the same methodology you are," Dr. Sharp said.
For respiratory specimens, store at 4°C and process within 12 hours if you can, and swabs may prove to be an acceptable transport vehicle for sputum samples.
Store urine samples at 4°C with or without preservative, and try to process within 24 hours to minimize the amount of significant culture result change. For stools, several enteric transport media provide acceptable storage conditions, and a saline preservative at 4°C also worked well for Salmonella and Campylobacter.