Lab Diagnostics: A Critical Tool in Managing & Treating Disease – Dr. Karen Whala
When you take your pet to the hospital because something is wrong, you can probably expect to answer a bunch of questions, submit your pet for a physical exam and many times, depending on the condition, be asked to have your pet submit blood and/or urine to further find out what is going on. Laboratory testing, aka “bloodwork”, includes a minimum of a complete blood count, chemistry panel and is crucial in detection, diagnosis and treatment of diseases in many patients. Lab testing also is used for monitoring effectiveness of treatment and can be as simple as testing the pH of a drop of urine to a PCR test on cheek swab to a complex MRI. Though it cannot be overestimated how critical to diagnosis lab tests are, it must also be emphasized that lab tests have annoying limitations and that sometimes, even if every test in the lab book were to be submitted, a diagnosis may still be elusive.
There are literally over 1,500 different tests available to veterinarians for dogs and cats alone and can involve testing such diverse samples as stool, hair, cheek swabs, skin, lung secretions and biopsies not to mention blood and urine. With so many tests to choose from, it can be challenging to choose the right test in order to arrive at the diagnosis as timely, inexpensively and least invasively as possible. Many owners may be unaware that they can help in this decision making process by providing as much history as possible. By recording when their pet became itchy or their appetite started waning or mentioning that they went on vacation 2 months ago to the coast. All this information helps guide diagnostics and sometimes therapeutics. In combination with a thorough physical exam, a veterinarian can sometimes narrow down the possibilities fairly well. I know that when I have a good history (answers provided to the pet nurse) and have performed a thorough physical exam, I enjoy the challenge of attempting to arrive at the correct diagnosis before any further testing has been performed. More than just a challenge, this helps guide diagnostic choices, minimize costs and reduces the time to effective treatment.
A recent case demonstrates this. A 6 year old adorable, yet quiet spayed female chihuahua came to the hospital because she was lethargic for the past 3 weeks and recently stopped eating. Her owners also reported dark yellow urine. Her other dogs were not showing any signs and she confirmed that her pet was limited to the house with no history of vomiting, diarrhea, coughing or sneezing. She was current on vaccines and has never traveled outside her hometown. Her physical exam revealed her body condition to be a grade 7/9 (4 and 5 are ideal weight). She was quieter than usual in the exam room and had a rapid pulse with a low grade murmur (new). Her gums were pale and the whites of her eyes were yellow tinged. A fundic exam (an ophthalmic exam that can occasionally detect abnormalities affecting blood pressure, bleeding disorders, infections and even neurological disease) revealed evidence of hemorrhage. Her abdomen palpated enlarged. Based on her history and physical exam, I was able to narrow down the possibilities but lab testing was still crucial to rule out potential diseases and arrive at a diagnosis. So a CBC (complete blood count), chemistry panel and urinalysis were initially submitted. I also submitted additional testing because certain tick borne diseases can appear to cause the same symptoms.
Her lab results were negative for liver, renal, thyroid and tick borne disease involvement. She had profound hemolytic anemia (hematocrit of 19% (normal is 35%+) which is a description rather than a definitive diagnosis. Her body was actively destroying its red blood cells and was ‘dumping’ the evidence into her urine and the break down products of the red blood cells was lending a pale yellow appearance to the whites of her eyes. Her murmur was due to profound anemia and ‘watery’ blood. This initial testing helped narrow down the diagnosis but didn’t offer the cause and thus further testing was indicated. We were able to proceed with initial treatment at this time but needed more information regarding why she was destroying her red blood cells. An x-ray of her abdomen and chest revealed no evidence of metastasis (which would have suggested a cancerous cause). An abdominal ultrasound revealed a large spleen but all other organs appeared normal on ultrasound. At this time (several days later), our girl was responding nicely to the immunosuppressant therapy and based on this response to therapy and our diagnostics so far, our tentative diagnosis was immune-mediated hemolytic anemia. A fancy description for self destruction of red blood cells which can occur for numerous reasons but very few can be proven. This is one of the limitations of diagnostics. We can often determine ‘what’ is wrong but there can be limitations on figuring out ‘why’. To this day, we were unable to determine why her body was destroying its red blood cells. Some possibilities that are reported in literature include medications, insect bites and vaccines with the vast majority of cases, even with extensive testing, bearing an unknown cause. So, because our pet responded to the therapy, her owner elected not to pursue further special testing and wanted to continue the therapy based on the diagnostics that were already performed. We continue to do hematocrit monitoring however, so that any drop in her hct can be promptly recognized and therapy can be adjusted accordingly. To this day, she continues to do well.
Though there are obvious limitations to lab diagnostics, they are critical to diagnosing, managing and treating disease.