Samples from Within
Some samples can only be obtained by breaking through the body's protective coverings (e.g., skin). Blood specimens are obtained in minimally invasive procedures conducted by specially trained physicians, nurses, or medical personnel. Collection of tissue specimens is a more complex process and may require a local anesthetic in order to obtain a specimen.
Because of the nature of these collections techniques, some 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 The sample is obtained by needle puncture and withdrawn by suction through the needle into a special collection tube. Some specimens may be obtained by a finger puncture that produces a drop of blood, such as that used for glucose testing. The procedure usually takes just a few minutes and hurts just a bit, typically when the needle is inserted or from the puncture of a lancet. See Tips on Blood Testing for more information.
Tissue Biopsy — Samples of tissue may be obtained from a number of different body sites, such as breast, lung, lymph node, or skin. Depending on the site and the degree of invasiveness, some pain or discomfort may occur. The time required to perform the procedure and for recovery can also vary greatly. These procedures are conducted by healthcare providers who have had specialized training. Tissue biopsies can be collected using procedures, such as:
- Needle biopsy — A needle is inserted into the site and cells and/or fluid are withdrawn using a syringe.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 excisional biopsy is a minor surgical procedure in which an incision is made and a portion or all of the tissue is cut from the site. A closed biopsy is a procedure in which a small incision is made and an instrument is inserted to help guide the surgeon to the appropriate site to obtain the sample. These biopsies are usually performed in a hospital operating room. A local or general anesthetic is used, depending on the procedure, so the patient remains comfortable. If a general anesthetic is used, recovery may take one to several hours.
Cerebrospinal Fluid (CSF) — A sample of cerebrospinal fluid is obtained by lumbar puncture, often called a spinal tap. It is a special but relatively routine procedure. It is performed while the person is lying on their side in a curled up, fetal position or sometimes in a sitting position. The back is cleaned with an antiseptic and a local anesthetic is injected under the skin. A special needle is inserted through the skin, between two vertebrae, and into the spinal canal. The health practitioner collects a small amount of CSF in multiple sterile vials; 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 their 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. Discomfort levels can vary greatly. The most common sensation is a feeling of pressure when the needle is introduced. Let your healthcare provider 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. These are generally more complex type of collections and often require some patient preparation, use of a local anesthetic, 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 trained healthcare specialist. Both types of samples are most often collected from the hip bone (iliac crest). In some instances, marrow collection may be collected from the breastbone (sternum). Almost all patients are given a mild sedative before the procedure, then asked to lie down on their stomach or side for the collection. The site is cleaned with an antiseptic and injected with a local anesthetic, treating it as a typical surgical field. When the site has numbed, the health practitioner inserts a needle through the skin and into the bone. For an aspiration, a syringe is attached to the needle and bone marrow fluid is aspirated. For a bone marrow biopsy, a special needle is used to collect 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. In some instances, the procedure may be repeated on the opposite hip (bilateral bone marrow), most often done as part of the initial diagnostic workup. The patient is then 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.
Amniotic fluid — A sample of amniotic fluid is obtained using a procedure called amniocentesis to detect and diagnose certain birth defects, genetic diseases, and chromosomal abnormalities in a fetus. Amniotic fluid surrounds, protects, and nourishes a growing fetus during pregnancy. A sample (about 1 ounce) of amniotic fluid is aspirated by inserting a thin needle through the belly and uterus into the amniotic sac, collecting both cellular and chemical constituents that are analyzed to detect certain genetic abnormalities that may be present.