Histopathology

Histopathology (or histology) involves the examination of sampled whole tissues under the microscope. Three main types of specimen are received by the pathology laboratory.

  1. Larger specimens include whole organs or parts thereof, which are removed during surgical operations. Examples include a uterus after a hysterectomy, the large bowel after a colectomy or tonsils after a tonsillectomy.
  2. Pieces of tissue rather than whole organs are removed as biopsies, which often require smaller surgical procedures that can be performed whilst the patient is still awake but sedated. Biopsies include excision biopsies, in which tissue is removed with a scalpel (e.g. a skin excision for a suspicious mole) or a core biopsy, in which a needle is inserted into a suspicious mass to remove a slither or core of tissue that can be examined under the microscope (e.g. to investigate a breast lump).
  3. Fluid and very small pieces of tissue (individual cells rather than groups of cells, e.g. within fluid from around a lung) can be obtained via a fine needle aspiration (FNA). This is performed using a thinner needle than that used in a core biopsy, but with a similar technique. This type of material is usually liquid rather than solid, and is submitted for cytology rather than histology

Cytopathology

Cytology is the study of individual cells and cytopathology is the study of individual cells in disease. Sampled fluid/ tissue from a patient is smeared onto a slide and stained (see techniques, below). This is then examined under the microscope by the anatomical pathologist to look at the number of cells on the slide, what types of cells they are, how they are grouped together and what the cell details are (shape, size, nucleus etc). This information is useful in determining whether a disease is present and what is the likely diagnosis.

Cytology is most often used as a screening tool; to look for disease and to decide whether or not more tests need to be performed. An example of screening would be the investigation of a breast lump. In combination with examination by the clinician and imaging tests, a needle aspirate of the lump submitted for cytology will show whether the breast cells are suspicious for cancer or look bland/ benign. If they look suspicious, a core biopsy with a larger needle may be performed which takes more tissue, allowing for a definitive diagnosis to be made before deciding what type of surgery is required (local removal of the lump or removal of the whole breast).

 

These tests are used to help diagnose, evaluate, and monitor people suspected of having Acute Coronary Syndrome (ACS).
MARKER WHAT IT IS TISSUE SOURCE REASON FOR INCREASE TIME TO INCREASE TIME BACK TO NORMAL WHEN/HOW USED

Cardiac Troponin

Regulatory protein complex; two cardiac-specific isoforms: T and I Heart Injury to heart 3 to 4 hours Remains elevated for 10 to 14 days Diagnose heart attack, risk stratification, assist in deciding management, assess degree of damage

High-sensitivity cardiac troponin
Currently not approved in U.S. but may be soon; it is routinely used in Canada, Europe

 Same as above, just measures the same protein at a much lower level Heart Injury to heart Within 3 hours of onset of symptoms Same as above Same as above; may also be elevated in stable angina and people without symptoms and indicates risk of future cardiac events (e.g., heart attacks)

CK

Enzyme; total of three different isoenzymes Heart, brain, and skeletal muscle Injury to skeletal muscle and/or heart cells 3 to 6 hours after injury, peaks in 18 to 24 hours 48 to 72 hours, unless due to continuing injury Frequently performed in combination with CK-MB; sometimes to detect second heart attack occurring shortly after the first

CK-MB

 Heart-related isoenzymes of CK Heart primarily, but also in skeletal muscle Injury to heart and/or muscle cells 3 to 6 hours after heart attack, peaks in 12 to 14 hours 48 to 72 hours, unless new or continuing damage Less specific than troponin, may be ordered when troponin is not available

Myoglobin

Oxygen-storing protein Heart and other muscle cells Injury to muscle and/or heart cells 2 to 3 hours after injury, peaks in 8 to 12 hours Within one day after injury Used less frequently; sometimes performed with troponin to provide early diagnosis

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