Imagine this clinical scenario: you are working the out-of-hours shift when a client brings in their five-year-old Golden Retriever – a known scavenger. The patient is presenting with anorexia, lethargy and abdominal pain. A quick ultrasound scan shows a small amount of free fluid in the abdomen. You suspect this is a case of septic peritonitis but cannot find any intracellular bacteria in the peritoneal fluid sample you took. You also cannot wait for results from bacterial culture, so you wonder if you can measure the glucose levels in the blood and peritoneal fluid instead to reliably confirm your working diagnosis.
You decide to consult the literature to explore whether the measurement of glucose levels in the blood and peritoneal fluid can be used to diagnose septic peritonitis in dogs.
Three papers were reviewed, all of which were diagnostic test validation studies (Bonczynski et al., 2003; Koenig and Verlander, 2015; Martiny and Goggs, 2019).
Sample sizes ranged from 18 to 39 dogs. All samples were mixed populations, presenting at primary or referral practices. All animals had naturally occurring peritoneal effusions and/or naturally occurring systemic inflammatory response syndrome.
The outcomes studied included:
- Glucose concentration in the blood, peritoneal fluid and peritoneal fluid supernatant
- Total nucleated cell count in peritoneal fluid
- Blood to fluid glucose differences
- Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of glucose concentration differences for:
- whole blood to peritoneal fluid
- plasma to peritoneal fluid
- plasma to peritoneal fluid supernatant
- Peritoneal fluid cytology for bacterial identification and culture
The studies were generally well planned, patient follow-up was good and all studies were carried out in a realistic clinical setting.
Limitations of the evidence
The main limitation of all the studies was the small sample size. Additionally, all studies collected data from patients in referral practices, where they may present with a more severe disease status than those seen in first-opinion clinics. Furthermore, all the studies only sampled the animals once, typically at the initial presentation.
All studies collected data from patients in referral practices, where they may present with a more severe disease status than those seen in first-opinion clinics
Bonczynski et al. (2003) and Martiny and Goggs (2019) analysed glucose measurements using blood chemistry and blood gas analysers, respectively – both of which are not always readily available in clinical practice.
Bonczynski et al. (2003) found the peritoneal fluid glucose concentration was significantly lower in dogs with septic effusions than those with non-septic ones. In septic dogs, peritoneal fluid glucose measurements under 50 mg/dl (under 2.8 mmol/l) were 57 percent sensitive and 100 percent specific, whereas a diagnostic sensitivity and specificity of 100 percent was identified when using blood to fluid glucose differences of over 1.1 mmol/l to diagnose septic peritonitis. Blood to fluid glucose difference was therefore shown to be more reliable for a diagnosis of septic peritonitis than peritoneal fluid glucose measurements alone.
Martiny and Goggs (2019) found that blood to fluid glucose gradients did not have a sensitivity, specificity or diagnostic accuracy of 100 percent. This was likely due to their requirement that all patients had an effusion and systemic inflammatory response syndrome diagnosed at presentation. In turn, this meant the septic peritonitis group and the control group of non-septic ascites (NSA) were clinically very similar and age-matched. The authors identified that blood-effusion gradients were significantly higher in dogs with septic peritonitis compared to the control group. By considering receiver operating characteristics, they also found that blood-effusion gradients can discriminate between septic peritonitis and NSA. However, the study did not identify a cut-off value for blood-effusion glucose gradients with reasonable sensitivity or specificity.
By considering receiver operating characteristics, they also found that blood-effusion gradients can discriminate between septic peritonitis and non-septic ascites
Koenig and Verlander (2015) measured glucose using a veterinary point-of-care (POC) glucometer, a tool commonly available in veterinary practice. They found that when using a cut-off value of over 1.1 mmol/l (over 20 mg/dl), whole blood to peritoneal fluid concentration differences were insensitive for diagnosing septic peritonitis. This was also the case for plasma to peritoneal fluid concentration differences. However, the authors found a plasma to peritoneal fluid glucose concentration difference of over 2.1 mmol/l (over 38 mg/dl) supported an accurate diagnosis of septic peritonitis in dogs with peritoneal effusions, with a diagnostic sensitivity of 88.2 percent and specificity of 100 percent, giving a diagnostic accuracy of 94.6 percent. They also found that plasma rather than whole blood produced significantly relevant differences when using a veterinary POC glucometer. However, there was no relevant difference when using peritoneal fluid rather than peritoneal fluid supernatant.
Summary of the findings
In summary, when using a veterinary POC glucometer, glucose measurements can be used to diagnose septic peritonitis when the blood plasma glucose level is over 2.1 mmol/l higher than the peritoneal fluid glucose level. When a biochemistry analyser is used, a whole blood glucose level of over 1.1 mmol/l higher than the peritoneal fluid glucose level can be used to diagnose septic peritonitis. This is only relevant when the peritoneal fluid is collected by abdominocentesis and not in a post-operative period.
At present, there is moderate evidence that glucose measurements are useful as a patient-side test for the diagnosis of septic peritonitis. The measurements are especially useful in cases where intracellular bacteria cannot be identified on cytology. However, the cut-offs reported are variable, and overall, there is not a single diagnostic test that is 100 percent sensitive and specific in repeated studies. Therefore, the results of the glucose measurements should be evaluated alongside other biomarker testing, imaging modalities and the clinical presentation of the patient. Glucose measurements cannot currently replace culture/sensitivity and cytology as the gold standard for the diagnosis of septic peritonitis.
Glucose measurements cannot currently replace culture/sensitivity and cytology as the gold standard for the diagnosis of septic peritonitis
Further research directly comparing the sensitivity, specificity and diagnostic accuracy when practitioners use different analysers and sample types could make the results easier to summarise and apply to general practice.
The application of evidence into practice should take into account multiple factors, not limited to individual clinical expertise, patient’s circumstances, owner’s values, the individual case in front of you, the availability of therapies and resources, and the country, location or clinic where you work.
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.