A history of recent estrus and typical clinical signs, especially vaginal discharge, should raise your suspicion for pyometra.
In patients lacking vaginal discharge, the diagnosis can be more challenging. An enlarged uterus may be palpated within the
abdomen; however, aggressive attempts at palpation should be avoided to prevent inadvertent uterine rupture. Other potential
causes of vaginal discharge or uterine enlargement, including pregnancy, estrus, hydrometra, mucometra, vaginitis, neoplasia,
and uterine torsion, need to be considered as differential diagnoses.
Laboratory findings in patients with pyometra are not specific for pyometra and frequently reflect the presence of inflammation
and secondary metabolic disturbances. The results of a complete blood count will often demonstrate a neutrophilia with a regenerative
left shift; however, a normal white blood cell count or even a neutropenia with a degenerative left shift may be identified
in animals with endotoxemia.7,12
Chemotactic chemicals released from the inflamed uterus attract neutrophils to the uterine lumen where they become sequestered.7 Eventually, the bone marrow may not be able to keep up with the demand for mature neutrophils, leading to a degenerative
left shift. A high white blood cell count may be seen after surgical removal of the uterus, as neutrophils are no longer sequestered.
Mild normocytic, normochromic anemia has been documented in dogs, possibly secondary to bone marrow suppression associated
with the uterine inflammation and its associated toxemia.7
The most commonly encountered biochemical abnormalities reported include elevated alkaline phosphatase and alanine transaminase
activities, and blood urea nitrogen (BUN), creatinine, globulin, and total protein concentrations.12
Bacterial endotoxemia and reduced liver perfusion are thought to contribute to the elevated liver enzyme activities. Dehydration
will frequently contribute to elevated BUN and creatinine concentrations, although concurrent kidney insufficiency in an older
dog may also be responsible for the azotemia.4,27 Kidney damage secondary to immune complex deposition has not been substantiated in recent studies.28,29 Hyperglobulinemia and elevated total protein concentrations can occur secondary to chronic inflammation and dehydration.
Although less commonly encountered, hypoglycemia can be attributed to septicemia.
Urinalysis findings can be variable. Many patients will have a high urine specific gravity secondary to dehydration. In other
patients, the urinalysis will reveal isosthenuria, hyposthenuria, proteinuria, or bacteriuria.7,10 The loss of urine-concentrating ability by the kidneys reported in some patients may be secondary to bacterial endotoxin
impairment of renal tubule function.10,12,28
Meanwhile, the presence of severe proteinuria at the time of treatment has been associated with the future development of
renal failure in some dogs.29 To retrieve urine for evaluation, a free-catch sample is preferred. Collecting urine by cystocentesis—even if performed
with ultrasound guidance—can lead to inadvertent uterine puncture and subsequent leakage of infectious material into the peritoneal
Abdominal radiography can raise suspicion for pyometra. Lateral radiographic projections may reveal craniodorsal displacement
of the small bowel and a contorted homogeneous tubular opacity in the caudoventral abdomen (Figure 1).30 The ventrodorsal radiographic projection may reveal cranial and medial displacement of the small bowel.30 Both tissue-dense uterine horns can sometimes be visualized.
Figure 1. A lateral abdominal radiograph of a dog with pyometra. The largely distended uterus can be visualized filling the
caudal and mid-abdomen. Cranial and dorsal displacement of the small bowel are evident.
However, radiography can be insensitive for detecting pyometra since uterine distention typically cannot be detected until
the diameter of the uterus is larger than that of the adjacent small bowels. In addition, radiography cannot distinguish pyometra
from other causes of uterine distension, such as mucometra or early pregnancy (prior to fetal skeletal mineralization).