section name header

Introduction ⬇

This test most commonly diagnoses primary atypical viral pneumonia caused by Mycoplasma pneumoniae; it is used to diagnose certain hemolytic anemias (e.g., cold agglutination disease) as well. The diagnosis depends on demonstrating a fourfold or higher increase in antibody titers between an early acute-phase blood serum sample and a blood serum sample taken in the convalescence phase, 7–10 days after the first sample. Positive reaction frequency and titer elevation both appear to be directly related to infection severity.

Patient’s serum is serially diluted, human red cells are added, and the test is incubated at 4 °C (refrigerator, 0 °C–10 °C). The cold agglutinin antibodies react optimally at 4 °C with the I antigen present on human red cells. The reaction is reversed by incubation of the agglutinated serum/cell mixture at 37 °C.

Normal Findings ⬆ ⬇

Procedure ⬆ ⬇

  1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.

  2. The sample should be prewarmed to 37 °C for at least 15 minutes before the serum is separated from the cells. This allows the cold agglutinating antibodies to be eluted from the red cell membranes so that they can be detected in the agglutination procedure using O-negative indicator cells (pooled group O donors).

Clinical Implications ⬆ ⬇

  1. With viral pneumonia, the titer rises 8–10 days after onset, peaks in 12–25 days, and decreases 30 days after onset. Up to 90% of people with severe illness exhibit positive titers.

  2. Chronic increased titer levels are associated with the following conditions:

    1. Cold antibody hemolytic anemia

    2. Chronic cold agglutinin disease

    3. Paroxysmal cold hemoglobinuria

    4. Severe Raynaud phenomenon (may lead to gangrene)

    5. B-cell chronic lymphocytic leukemia

  3. More important than any single high value is the rise in titer during the course of illness. The titer usually decreases by 4–6 weeks after the onset of illness.

  4. Transient increases in titers are associated with primary atypical viral pneumonia, IM, measles, mumps, CMV, congenital syphilis, hepatic cirrhosis, and trypanosomiasis.

Clinical Alert

A negative test does not rule out infection because only 30%–50% of patients with M. pneumoniae infection will develop cold agglutinins

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. See Interpreting Results of Immunologic Tests. Cold agglutinin titers rise during the second and third week of illness before rapidly returning to baseline levels. The test should be repeated at appropriate intervals.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. A high cold agglutinin titer interferes with blood typing and cross-matching.

  2. High titers are sometimes spontaneous in older persons and may persist for years.

  3. Antibiotic therapy may interfere with cold agglutinin development.