From the Guidelines
Prolonged exposure to red blood cells (RBCs) can significantly affect laboratory tests, particularly those measuring folate status, as RBC folate levels reflect long-term folate status and can be altered by prolonged exposure to RBCs. When considering the impact of prolonged exposure to RBCs on laboratory tests, it is essential to recognize that this can lead to changes in various parameters due to the continued metabolism and leakage of intracellular contents from RBCs. The key laboratory tests affected by prolonged exposure to RBCs include:
- Folate status, as measured by RBC folate levels, which can be altered due to the prolonged exposure, potentially leading to inaccurate assessments of long-term folate status 1.
- Other tests may also be indirectly affected, such as plasma homocysteine concentrations, which are used as a functional marker of folate status but can also be influenced by the status of vitamins B2, B6, and B12, as well as renal impairment 1. It is crucial to process blood samples promptly, ideally within a short timeframe of collection, and store them appropriately if processing is delayed to minimize the effects of prolonged RBC exposure on laboratory results. Understanding these effects is vital for the accurate interpretation of laboratory results, especially when sample processing is delayed, to ensure that any abnormalities detected are genuinely reflective of the patient's condition rather than artifacts of prolonged RBC exposure. In the context of folate status assessment, using the gold standard technique of microbiological assay (MBA) with Lactobacillus rhamnosus, and taking pre-analytical precautions to protect folate from degradation, can help ensure reliable results 1.
From the Research
Laboratory Tests Affected by Prolonged Exposure to RBCs
Prolonged exposure to red blood cells (RBCs) can lead to abnormal laboratory test results due to hemolysis, the breakdown of RBCs. The following laboratory tests can be affected:
- Complete Blood Count (CBC) with differential 2, 3, 4
- Reticulocyte count 2, 5
- Lactate dehydrogenase (LDH) levels 5
- Unconjugated bilirubin levels 5
- Haptoglobin levels 5
- Direct antiglobulin test 5
- Peripheral blood smear 5
- Red blood cell indices, including mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, and red cell distribution width 2, 4
- Hemoglobin and hematocrit levels 2, 4
- White blood cell count and differential 2, 4
- Platelet count 2
Mechanisms of Hemolysis
Hemolysis can occur through various mechanisms, including:
- Poor deformability leading to trapping and phagocytosis 5
- Antibody-mediated destruction through phagocytosis or direct complement activation 5
- Fragmentation due to microthrombi or direct mechanical trauma 5
- Oxidation 5
- Direct cellular destruction 5
Clinical Interpretation of Laboratory Results
The interpretation of laboratory results requires a comprehensive understanding of the strengths, limitations, and clinical implications of each test 6, 3. A structured approach to evaluating abnormal laboratory results can help clinicians recognize when a subspecialty consultation is necessary and when it may be circumvented 3.