From the Guidelines
Critical Ranges for Major ICU Laboratory Tests
The critical ranges for major Intensive Care Unit (ICU) laboratory tests, particularly for blood glucose, are within 12.5% of a reference standard (or within 0.55 mmol/l for readings <5.5 mmol/l) for 98% of readings, and within 20% for the remaining 2% 1.
Blood Glucose Measurement Standards
- For patients with invasive vascular monitoring, central laboratory analyzers and blood gas analyzers should perform to international standards of ±0.4 mmol/l (or ±8% above 5 mmol/l) 1.
- For patients without invasive vascular monitoring, glucose meters should meet the minimum standard of 98% of readings within 12.5% of a reference standard (or within 0.55 mmol/l for readings <5.5 mmol/l), and the remaining 2% within 20% 1.
- Arterial or venous blood samples are preferred over capillary samples to minimize errors and factitious results 1.
- Point-of-care glucose meters are subject to various errors and interferences, including user interface, patient/therapy factors, and physiologic factors, which can affect their accuracy in the ICU setting 1.
Clinical Practice Recommendations
- Establish a hierarchy of sampling procedures to reduce between-tester differences and prioritize arterial or venous blood sources over capillary testing 1.
- Choose blood glucose analyzers that meet international standards, and consider using blood gas analyzers as the default analyzer in ICUs 1.
- Understand the limitations of specific devices and components of FDA 510(k) summaries to minimize errors and ensure accurate results 1.
From the Research
Critical Ranges for Major ICU Laboratory Tests
The critical ranges for major Intensive Care Unit (ICU) laboratory tests are not strictly defined, as they can vary depending on the specific patient population and the context of the test results. However, several studies have investigated the distribution of laboratory values in ICU patients and their association with patient outcomes.
- A study published in 2018 2 found that the distribution of ICU laboratory values differs significantly from the standard reference range, with a mean overlapping coefficient of 0.51.
- Another study published in 2018 3 derived ICU-based reference intervals from measurements obtained at ICU discharge in patients who survived for more than 1 year and found that medians of 14 of 35 ICU-based ranges were outside the standard reference interval.
- A study published in 2014 4 found that customized reference ranges for laboratory values can decrease false positive alerts in ICU patients, but disagreement among clinicians about which laboratory values should be indicated as abnormal limits the development of customized reference ranges.
Laboratory Tests and Patient Outcomes
Several studies have investigated the association between laboratory tests and patient outcomes in the ICU. For example:
- A study published in 2018 3 found that lactate had the strongest relation with hospital mortality on ICU admission, and variability was independently related with hospital mortality in 30 of 35 measurements.
- A study published in 2018 2 found that all laboratory values for the best outcome group differed significantly from those in the worst outcome group, and both the best and worst outcome group curves revealed little overlap with and marked divergence from the reference range.
Routine Laboratory Testing in the ICU
Routine laboratory testing is a common practice in the ICU, but there is limited evidence to support the current practice of laboratory testing in most ICUs. For example:
- A study published in 2007 5 found that laboratory testing should be conducted as part of a therapeutic approach to a clinical problem, mindful of pretest probability of disease, the performance of the selected test, and the relative benefits and risks of testing.
- A study published in 2000 6 found that clinical and operational factors specific to each ICU appear to impact on routine blood tests, and guidelines for their use may not influence the frequency of the most commonly performed routine blood tests.