What's a Pathologist, anyway?

This question may be old hat for some of you reading this blog, but friends and family might not have a clear idea of what we do and how we fit into medicine - in the US or Kenya.  So if you've ever wondered what we do, read on!

Pathologists are the physicians you never see in person.  We are diagnostic physicians.  Even if you don't see us, as pathologists we see essentially every patient (or something from every patient) in every hospital, doctor's office, and outpatient clinic.  We're behind the scenes, but every single specimen that comes from a patient - tissue, blood, snot, pus, urine, stool, you name it - makes it way to our labs.

We are trained like any other MD out there: medical school, residency (3-4 years), and usually fellowship (specialty/sub-specialty) training.  We make diagnoses by looking at tissue under the microscope (tens of millions of results annually in the US) and by providing laboratory values (billions of results annually in the US).  There is an oft-cited piece of pathology lore that states "70% of medical decisions" are based on these data - unfortunately, I can't find anything other than expert opinion to support this statement.

We tend to split ourselves into Anatomic Pathologists and Clinical Pathologists

• Anatomic Pathology (AP) - AP is the branch of pathology that makes diagnoses by looking at tissue, both with the naked eye ("the gross examination") and under the microscope.  We look at biopsies (small bits of tissue to make an initial diagnosis) as well as big resections, like mastectomies. Our work defines the disease process (cancer vs not-cancer), whether the diseased tissue is out (margin status), and many other critical clinical questions.
• Biopsies: If you've ever had a skin biopsy to rule out basal cell carcinoma, squamous cell carcinoma, melanoma, or to evaluate a rash, you've had a pathologist.  Similarly, if you've ever had a colonoscopy to look for "polyps" or inflammation, it's the pathologist who looks at those little biopsies to look for cancer ("neoplasia" is a better word) or other changes. 
• Resections: When a piece of an organ or body site is removed, we make a series of determinations about disease type, extent of disease, severity of the changes, and perhaps most importantly: did the surgeons get it all?  
• Intraoperative Consultation: An important role for the pathologist is to work with surgeons right in the middle of the surgery!  Surgeons will give us a sample of tissue and in 20min or less, we get back to them with information that changes the rest of their operation. Sometimes this is diagnostic ("is it cancer?"), sometimes the question is about extent ("did we get it all out"), and sometimes it's about whether more tissue needs to come out ("are lymph nodes involved").  

• Clinical Pathology (CP) - CP is commonly referred to as "Laboratory Medicine" and is the practice of running ALL of the laboratories in the hospital, from Chemistry to Microbiology. We make sure that the results are accurate, reported quickly, and work with our clinical colleagues to help interpret what test results mean.  
• Traditional Labs - these include chemistry, microbiology, immunology, virology, coagulation testing, and hematology.  In these labs, we make diagnoses of infectious diseases and what drugs can kill the infectious organism (or virus), why patients are bleeding, whether they have dangerous blood disorders such as Sickle Cell disease or thalassemias, how well the patient's liver or kidneys work, concentrations ("levels") of potentially toxic or life-saving drugs, and whether patient has taken any street drugs or toxic substances.
• Transfusion Medicine and Blood Banking - running a blood bank is an art unto itself, requiring a range of laboratory testing ("blood typing" and testing for infectious disease are two important examples), blood collection, screening donors and donated products to make sure the donated product is safe, storage of blood products, as well as managing and preventing transfusion reactions.  
• Clinical Informatics - informatics is the practice of making sure information flows appropriately, completely, and efficiently.  As Pathologists, we are uniquely poised to understand and improve how clinical information (test results, doctors notes, nursing records, etc) flow through the lab and the entire hospital system.  Clinical informatics is part of both AP and CP, although CP has a higher volume of results.

• Hybrid Specialties that cross AP & CP - Not everything lumps nicely together.  
• Hematopathology - Hematopathology is the diagnosis of leukemias, lymphomas, and other related disorders of blood cells and bone marrow.  We use a range of tools - microscopes, molecular testing (see below), flow cytometry, and clinical data to make these critical diagnoses.  Hematopathology has been an exciting, rapidly growing area of medicine and has included lots of technological innovation (like clinical use of flow cytometry).
• Molecular Pathology & Genetics - the National Institute's of Health Human Genome Project was completed in 2003 with the publication of the first complete sequence of human DNA! The resulting data and the extraordinary technologies that arose from that effort still enormous potential to influence how we care for patients.  We routinely use the technology and insights from this basic science initiative in Molecular Pathology and Genetics.  We work closely with clinicians, including Genetic Counselors, to decide who needs genetic testing and what types.  We look for inherited conditions that place patients at risk for bleeding, infections, or cancer.  We look at cancers taken out of patients to look for driving mutations or genetic changes for which we have specific medications!

• Research - many pathologists also do research.  This can range from basic science  to clinical/translational research to projects in epidemiology and public health.  I won't discuss this here, but as someone interested in basic science research I feel this deserves a shout out.