Samples from within
Some samples can only be obtained by breaking through the body’s protective coverings (e.g., skin). Blood samples and tissue specimens, for example, are obtained in minimally invasive procedures conducted by specially trained physicians, nurses, and medical personnel.
Because of the nature of these collections techniques, some patient pain or discomfort may be involved. Knowing what the procedure involves may help alleviate some anxiety when having to undergo these types of sample collections. For more on this, see the article Coping with test pain, discomfort, and anxiety.
Some common examples of these kinds of samples include:
Blood — Blood samples can be collected from blood vessels (capillaries, veins, and sometimes arteries) by trained phlebotomists or medical personnel. The sample is obtained by needle puncture and withdrawn by suction through the needle into a special collection tube. The procedure usually takes just a few minutes and hurts just a bit, typically when the needle is inserted or withdrawn. See Tips on blood testing for more information.
Tissue biopsy — Samples of bodily tissue may be obtained from a number of different body sites such as breast, lung or skin and, depending on the site, may involve varying degrees of invasiveness and pain or discomfort. The time required to perform the procedure and for recovery can also vary greatly. These procedures are conducted by physicians and nurses who have had specialized training. Biopsies can be collected using procedures such as:
- Needle biopsy — A needle is inserted into the site and cells or fluid are withdrawn using a syringe. A slight pinch may be felt at the site of needle insertion. Usually no recovery time is required, and slight discomfort may be experienced afterwards.
- An open biopsy is a minor surgical procedure in which an incision is made and a portion of tissue is cut from the site. A closed biopsy is a procedure in which an incision is made (usually smaller than an open biopsy) and an instrument is inserted to help guide the surgeon to the appropriate site and to obtain the sample. These biopsies are usually performed in a hospital operating room. A local or general anaesthetic is used, depending on the procedure, so the patient remains comfortable. If a general anaesthetic is used, recovery may take one to several hours.
Cerebrospinal fluid (CSF) — A sample of cerebrospinal fluid is obtained by lumbar puncture, sometimes called a spinal tap. It is a special but relatively routine procedure. It is usually performed while the person is lying on his or her side in a curled up fetal position but may sometimes be performed in a sitting position. The back is cleaned with an antiseptic and a local anaesthetic is injected under the skin. A special needle is inserted through the skin, between two vertebrae, and into the spinal canal. The doctor collects a small amount of CSF in multiple sterile vials. Then the needle is withdrawn and a sterile dressing and pressure are applied to the puncture site. The patient will then be asked to lie quietly in a flat position, without lifting his head, for one or more hours to avoid a potential post-test spinal headache. The lumbar puncture procedure usually takes less than half an hour. For most patients, it is a moderately uncomfortable to somewhat painful procedure. The most common sensation is a feeling of pressure when the needle is introduced. Let your doctor know if you experience a headache or any abnormal sensations, such as pain, numbness, or tingling in your legs, or pain at the puncture site.
Other body fluids such as synovial fluid, peritoneal fluid, pleural fluid and pericardial fluid are collected using procedures similar to that used for CSF in that they require aspiration of a sample of the fluid through a needle into a collection vessel, such as a syringe or specimen container. They often require some patient preparation, use of a local anaesthetic, and a resting period following sample collection. For details, see the descriptions for arthrocentesis, paracentesis, thoracentesis, and pericardiocentesis.
Bone marrow — The bone marrow aspiration and/or biopsy procedure is performed by a doctor or other trained specialist. Both types of samples may be collected from the hip bone (pelvis), and marrow aspirations may be collected from the breastbone (sternum). In children, samples may also be collected from a vertebra in the back or from the thigh bone (femur). The most common collection site is the top ridge (iliac crest) of the hip bone. Some patients are given a mild sedative before the procedure, and then the patient is asked to lie down on his or her stomach or side for the collection and their lower body is draped with cloths so that only the area surrounding the site is exposed. The site is cleaned with an antiseptic such as iodine, and injected with a local anaesthetic. When the site has numbed, the doctor inserts a needle through the skin and into the bone. For an aspiration, the doctor attaches a syringe to the needle and pulls back on the plunger. This creates vacuum pressure and pulls a small amount of marrow into the syringe. For a bone marrow biopsy, the doctor uses a special needle that allows the collection of a core (a cylindrical sample) of bone and marrow. Even though the patient’s skin has been numbed, the patient may feel brief but uncomfortable pressure (pulling and/or pushing) sensations during these procedures. After the needle has been withdrawn, a sterile bandage is placed over the site and pressure is applied. The patient is then usually instructed to lie quietly until their blood pressure, heart rate, and temperature are normal, and then to keep the collection site dry and covered for about 48 hours.