Agreement between Parallel Canine Blood and Urine Cultures: Is Urine Culture the Poor Man's Blood Culture?

Abstract

Bloodstream infections are a significant cause of morbidity and mortality in critically ill dogs, but due to cost and difficulties in sample acquisition, blood cultures are infrequently obtained. In ill dogs, urine cultures may be recommended as surrogates for blood cultures. In order to determine the outcome agreement between parallel urine and blood cultures, we retrospectively analyzed parallel blood and urine specimens submitted for culture from dogs at the NC State Veterinary Hospital between 2011 and 2016. Positive cultures were reported from 15% of the submitted blood specimens and 23% of the submitted urine specimens. A total of 295 urine and blood samples were submitted in parallel, with positive growth demonstrated in 14 concordant and five discordant pairs. A kappa statistic comparing blood and urine culture outcomes was 0.266 (fair) when all parallel growth was included, including concordant and discordant results, and 0.170 (poor) when restricted to parallel concordant growth. The sensitivity of urine to reflect concordant bloodstream bacterial organisms was 30%, with a specificity of 87%. The positive and negative predictive values were 30% and 88%, respectively. Of dogs with both specimens positive on bacterial culture, 7 of 7 (100%) with suspected urogenital infection sources were concordant. All dogs with discordant bloodstream and urinary infections were immunosuppressed. Urinary coagulase-positive isolates were most likely to be concordant with bloodstream infections. In conclusion, we found that urine culture is neither a substitute nor a screen for blood culture. Blood cultures should be performed in any potentially septic animal, especially those that are considered immunosuppressed.

Retrospective evaluation of the utility of blood cultures in dogs (2009–2018): 45 cases

“…The yield of positive blood cultures matched our hypothesized proportion of 20%, which was toward the lower end of the range of previously reported literature 3–7,9,11 . Given the low number of submissions and reasons for blood culture that we documented, it is likely that this cohort reflects a highly selected population whereby the diagnosis was obscure, blood culture was thought to be of high yield, or direct culture from the source of infection was difficult.…”

“…Routine attainment of blood cultures before commencing antimicrobial therapy is recommended in people with sepsis 1 . Blood culture is useful for identifying infecting bacteria and determining antimicrobial susceptibility to guide antimicrobial escalation or de‐escalation 2,3 . There is no consensus on obtaining blood cultures routinely in companion animals with suspected sepsis, and there is a paucity of evidence concerning their utility.…”

“…There is no consensus on obtaining blood cultures routinely in companion animals with suspected sepsis, and there is a paucity of evidence concerning their utility. The reported yield of positive blood culture in varied cohorts of dogs and cats is 15%–49% 3–9 . However, these studies were not necessarily focused on the general utility of blood culture, and many are outdated 4,6,7 …”

Clinical features, outcome, and illness severity scoring in 32 dogs with urosepsis (2017–2018)

“…In a retrospective study of histopathologically confirmed pyelonephritis in dogs, only 79% of dogs had positive urine cultures. 33 The prevalence of urosepsis may therefore be underestimated if culture-negative dogs are excluded. The current study did not exclude dogs if they had negative culture results, as other compelling diagnostic tests (eg, cytology, diagnostic imaging, intraoperative findings) were supportive of an infection.…”

“…Although poor agreement was found between parallel blood and urine cultures overall in 1 retrospective study, blood and urine cultures in 7 of 7 dogs with known urogenital disease were concordant. 33 Acquiring blood cultures, however, may be impractical, technically challenging, and expensive. Furthermore, a positive blood culture is not required for the diagnosis of sepsis, and a negative culture does not rule it out.…”