What is the difference between routine and culture blood (or stool) tests?

We hope our article aimed at helping you understand the values of a lipid test report was valuable. Today, as part of a mini-series, we help you decode routine and culture tests, and what differentiates them.

In medical diagnostics, culture tests for blood and stool serve distinct but complementary purposes. While routine tests offer a general health overview and can flag potential issues, culture tests precisely identify pathogens, guiding targeted treatment strategies.

Dr Richa Agarwal, MD, Pathology, Wockhardt Hospitals, Mumbai Central emphasised that a pathology laboratory plays a pivotal role in healthcare by conducting a comprehensive array of diagnostic tests on various bodily samples including urine, stool, blood, body fluids, and tissue. “These tests are crucial for aiding clinicians in diagnosing a wide spectrum of conditions such as diabetes, infections, and potentially cancerous diseases. Each sample offers unique insights into a patient’s health status, guiding medical professionals towards accurate diagnoses and appropriate treatment plans,” said Dr Agarwal.

A routine test, such as a Complete Blood Count (CBC), provides a broad assessment of an individual’s overall health. It measures various components of the blood like red blood cells, white blood cells, and platelets, offering insights into conditions such as anemia, infections, and clotting disorders. “Stool routine tests evaluate physical characteristics and detect issues like gastrointestinal bleeding, malabsorption, or the presence of parasites,” explained Dr Janakiram Bobbillapati, HOD molecular biology, microbiology, and Serology at TRUSTlab Diagnostics.

lood cultures are essential for diagnosing severe infections like sepsis, endocarditis, and bone infections (Source: Getty Images/Thinkstock)

In contrast, culture tests specifically aim to identify infectious agents. Blood cultures are essential for diagnosing severe infections like sepsis, endocarditis, and bone infections. “By incubating a blood sample, any present bacteria or fungi can be grown, identified, and tested for antibiotic sensitivity. Stool cultures target gastrointestinal infections by detecting pathogens like Salmonella, Shigella, and E. coli. These tests help pinpoint the exact cause of symptoms such as gastroenteritis, food poisoning, and chronic diarrhea,” noted Dr Bobbillapati.

A culture report is interpreted based on the sample type. “A urine culture is considered significantly positive when an organism has grown to more than a certain number of colonies (mostly 105 colonies/ml for a urine sample). Any growth in blood or stool culture is significant,” said Dr Shelly Mahajan, lab director, Mahajan Imaging and Labs.

A positive report indicates the presence of infection of the urinary tract/gastro-intestinal tract/ blood (depending on the sample type) that requires the attention of the health care provider. Hence, it is advisable to immediately consult a healthcare provider when a culture report comes positive, to start proper treatment. A negative culture report indicates that there is no infection in the sample and other causes of the symptoms should be explored,” said Dr Mahajan.

The process of collecting samples, whether blood or stool, requires strict adherence to sterile techniques and proper preparation protocols, urged Dr Agarwal. “This ensures the integrity of the samples and minimises the risk of contamination, thereby enhancing the accuracy of diagnostic results. In some clinical scenarios, stool culture may prove more sensitive than blood culture in detecting certain pathogens, highlighting the importance of selecting the most appropriate diagnostic approach based on the patient’s symptoms and clinical presentation,” said Dr Agarwal.

Beyond technical procedures, clinical assessment of the patient is paramount before requesting diagnostic tests. “This holistic approach ensures that all relevant symptoms and medical history are considered, thereby optimising the diagnostic process and facilitating timely and effective treatment decisions. By integrating clinical expertise with advanced diagnostic capabilities, pathology laboratories play a critical role in improving patient outcomes and enhancing overall healthcare delivery,” said Dr Agarwal.

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