Centrifuged Information and Courses from MediaLab, Inc.

When blood is present in a CSF specimen, it is necessary to determine whether the blood is due to a traumatic puncture or to a pathologic condition. There are several clues to help make this distinction: Traumatic tap:More blood is present in tube 1 than in tubes 2, 3, or 4.When sample is centrifuged within one hour, supernatant is clear.Blood clots on standing.Subarachnoid or cerebral hemorrhage:Blood is evenly distributed in all tubes.When sample is centrifuged within one hour, supernatant is pink or yellow.Blood does not clot on standing.

It is important to recognize that xanthochromia is the appearance of color in the supernatant of a fresh, centrifuged CSF sample. There are a variety of causes for the appearance of this color. Therefore, it is important that xanthochromia be reported. The physician is responsible for determining the reason for its presence.

The pH of the urine must be approximately 7 or less in order to avoid false negatives with this test. If the pH exceeds 7, add 33% acetic acid dropwise to acidify the specimen to a pH of 7. If the specimen is cloudy, it should be centrifuged before SSA reagent is added. Daylight or fluorescent light is recommended when interpreting results. Quality control checks should be performed by testing known negative and positive specimens or controls.

Antibodies of the ABO system cause agglutination of saline-suspended red cells at 4°C to 20°C. Heating to 37° weakens the reaction. “Naturally” occurring ABO antibodies may not be strong enough to agglutinate cells without centrifugation. Thus, testing serum for the presence of anti-A or anti-B has classically been performed using the tube system in which serum and cells added to a test tube are centrifuged and then evaluated for agglutination. A slide test has also been performed for forward reactions. Although tube tests are still in wide use, newer systems utilizing other technology such as gel agglutination are becoming more prevalent. The image on this page illustrates agglutination reactions observed with the tube system, from 4+ in the topmost image, to 0 in the lowest image. ABO reactions should be strong. Weak or missing reactions occur, but must be "resolved" before blood products can be released.4+ agglutination: Red blood cell button is a solid agglutinate; clear background.3+ agglutination: Red blood cell button breaks into several large agglutinates; clear background.2+ agglutination: Red blood cell button breaks into many medium-sized agglutinates; clear background; no free red blood cells.1+ agglutination: Red blood cell button breaks into many small clumps barely visible macroscopically; background is turbid; many free red blood cells.Negative: No agglutinated red blood cells present; red cells are observed flowing off the red blood cell button during the process of grading.Other reaction which may occur are the mixed-field reaction, in which mixtures of agglutinated and unagglutinated red blood are present; and hemolysis, in which red cells are hemolyzed by the antibody. Both of these patterns are considered positive reactions.

Reverse typing refers to the testing of a patient's serum for the presence of ABO antibodies. The patient's serum is mixed with known red cells in a test tube. A specified number of drops of patient serum are placed into each of three properly labeled tubes. A specified number of drops of known A1 cells are added to the A tube, and a specified number of drops of known B cells are added to the B tube. The tubes are mixed by gently shaking, centrifuged, and observed against a well-lit white background for the presence of hemolysis in the supernatant fluid. The cell button is then gently dispersed and inspected for agglutination, again using a well-lit background. Hemolysis or agglutination is a positive reaction. The expected reactions can be seen in the table on the following page.

Hemolysis means the breakup of fragile red blood cells within the specimen, and the release of their hemoglobin (the red oxygen carrying substance present within the red cells), and other substances, into the plasma.A hemolyzed specimen is one which has undergone hemolysis. A hemolyzed specimen can be recognized after it is centrifuged by the red color of the plasma.

Serum is the fluid that is left over the coagulum after the specimen is centrifuged (spun down). Serum contains all the same substances as plasma, except for the coagulation proteins, which are left behind in the blood clot.

In order to test collection containers for sperm collection, the sperm must be held in the container for several hours to ensure that neither the numbers nor motility are adversely affected. Numbers will decline if the sperm adhere to the container. Motility will decline if the container is toxic. One method of testing involves removing sperm from semen. The specimen would be centrifuged and the sperm pellet diluted in a small volume of culture medium containing an energy source and at least 0.5% of a protein, such as serum albumin. The processed sperm specimen would be placed in the container to be tested. Total count and motility of the sperm would be tested at the start of incubation and 24 hours later. The container is non-toxic if the motility at the end of 24 hours is no less than 50% of the original value.

The urine microscopic exam is performed on a centrifuged urine sediment. The sediment contains all the formed elements or insoluble materials that have accumulated in the urine through its passage from the kidney to the lower urinary tract. These formed elements include cells, casts, crystals and miscellaneous structures.