Sampling techniques in cytology
This is the analysis of cells that are shed from body surfaces. Examples include the lining cells of the uterine cervix (mouth of the womb) and of the bladder. The analysis of cells from the cervix is a minimally invasive procedure called a cervical or Pap smear. This involves the insertion of a speculum into the vagina to allow the clinician to directly view the cervix. The cervix is then gently brushed to retrieve cervical cells which are put into a glass vial of fixative at the bedside and submitted to a laboratory for examination.
The analysis of cells from within a mass or organ. This involves a more invasive sampling procedure called Fine Needle Aspiration (FNA). A needle is inserted into the area of the body being examined, sometimes with the use of imaging (e.g. ultrasound or CT scan) to ensure that the suspicious area is being sampled. This procedure may be performed after injection of local anaesthetic to numb the skin, or even under light sedation if involving a deep organ or tissue. The cells retrieved are expressed onto a slide and prepared in a similar way to the cervical smear. If fluid is aspirated (e.g. within from a thyroid cyst), it may first be spun by a centrifuge so that the cell-containing sediment collects at the bottom of the test tube, allowing the best material to be sampled for examination.