increases by at least 25 percent following an inflammatory response. Values can increase to 1000 times normal. Some of the inflammatory markers are specific while others are non-specific to the source of inflammation. Tracking the positive acute phase proteins to determine when inflammatory process wanes may be misleading if inflammation improves in one area while other underlying areas of inflammation may be present. Table 1 categorizes selected acute phase proteins as either positive or negative.
Negative acute phase proteins plummet in the presence of inflammation. Levels decrease by at least 25 percent. For example, a 25 percent drop in an albumin of 3.0 g/dL would be 2.25 g/dL. The albumin does not evaporate or disintegrate. It simply shifts from the extravascular space to the plasma.
Table 1. Selected Acute Phase Proteins
| Positive Acute Phase Proteins | Negative Acute Phase Proteins |
| •C-reactive protein (CRP) | •Albumin |
| •hs-CRP | •Prealbumin |
| •Fibrinogen | •Transferrin |
| •Plasminogen-activator-inhibitor 1 (PAI-1) | •Insulin-like growth factor 1 |
| •Serum amyloid A | |
| •Ferritin | |
| •Ceruloplasmin |
Reference Standards
Standard laboratory reports are referenced using suggested normal or age-appropriate values. Remember that many reference standards were developed based upon clinical research using primarily young and middle aged adults. Clinical research on the very young and very old is limited. Reference standards may not apply to these age groups. This is of particular concern in assessing the growing elderly population because their norms appear to be slightly lower or higher than the standards, but the acceptable difference has yet to be defined. Some manufacturers of laboratory assay equipment have developed age reference standards using their databases. The director of your institution's laboratory will be able to assist you in evaluating the available database and in incorporating the equipment specific reference standards into the laboratory reports generated for each individual.
Equipment
The most accurate measure of changes in nutritional status is using laboratory results from the same institution. Comparing laboratory results from different institutions can be like comparing apples to oranges. Each institution establishes reference standards and laboratory procedures for each test as suggested by the manufacturer. Other sources of variation include equipment used, the degree of equipment calibration and the skill of the technician.
Considerations for Requesting Laboratory Tests
Historically, the physician made all healthcare diagnostic decisions exclusively. In managed care, the multidisciplinary teams work together to make diagnostic recommendations to improve outcomes. As a member of the health care team, it is important to know the clinical value of a test related to its sensitivity, its specificity, its predictive value and the incidence of the disease in the population tested.
Sensitivity refers to the ability of a test to correctly identify individual who truly have a disease. Specificity refers to the ability of a test to correctly identify those individuals who do not have the disease. Sensitivity and specificity do not change with different populations of ill and healthy patients. Predictive value refers to the ability of a screening test result to correctly identify the disease state. The predicative value of the same test can vary considerably with age, gender and geographic location.
As part of the critical thinking matrix of the NCP, it is vital that the nutrition professional consider the following questions when requesting additional laboratory tests.
1) Will the outcome actually change the nutrition plan of care?
If not, then why are you requesting the test be done?
2) Is the test cost-effective?
The cost of lab tests is based on a variety of factors including the volume of individual tests or panels of tests processed at the lab. Lab tests that must be sent to another lab to be processed are considerably more expensive than anything done in house.
3) Is your goal for the patient consistent with their treatment goals and advanced directives?
Be sure to talk with the patient or family to clarify purpose of more testing and how the results might change the plan of care Confirm that additional testing is desired.
Communication of Results
Clinical Laboratory Values
There are two systems for reporting clinical data either in conventional units or International Units (SI). The preferred method for reporting clinical laboratory data is in terms of International Units (SI Units). "SI Units" term is an abbreviation for le Système International d’Unités or International System. The reason for the change to SI units is to have an international standard for reporting research and medical data.
Laboratory Assessment of Nutritional Status: Bridging Theory & Practice provides both conventional units and SI units since both are used widely. Table 2 includes conversion factors for selected laboratory tests.
| Conventional Units can be converted to SI Units using this formula: |
| Conventional Units x conversion factor = SI Unit |
| SI Units can be converted to Conventional Units using this formula: |
| SI Unit ÷ conversion factor = Conventional Unit |
Table 2 provides conversion factors for selected values in Clinical Chemistry.
Table 2. Selected SI Units & Conversion Table for Values in Clinical Chemistry
| Component | Conventional Reference values/ Units | Conversion factor | SI Reference Values/ Units |
| Alanine Aminotransferase (ALT) (S) | 5-40 U/L | 1.0 | 5-40 U/L |
| Albumin (S) |
|
