Version 1.019 Feb 2020 Disclaimer: This infographic is not a validated clinical decision aid. This information is provided without any representations, conditions, or warranties that it is accurate or up to date. BMJ and its licensors assume no responsibility for any aspect of treatment administered with the aid of this information. Any reliance placed on this information is strictly at the user's own risk. For the full disclaimer wording see BMJ's terms and conditions: © 2020 BMJ Publishing Group Ltd. Your results may vary A tool for visualising the variability of lab test results Interactive Interpreting results can be challenging for patients and clinicians alike. Results can be affected by measurement uncertainty, and by variation caused by biological processes. This tool (based on data in the article below) is designed to help you decide if two consecutive results can be considered truly different after these kinds of variation have been taken into account. 1 Choose a test 2 3 4 Adjust variables Enter lab results View estimates These boxes are automatically populated with reasonable estimates of the analytic variation (authors’ lab) and biologic variation (published research). These can be adjusted as needed.
Analytic variation
Biologic variation Confidence level
Normal range (reference interval) Low High
Enter one or, if available, two serial lab results The minimum change required to conclude that two serial measurements are likely different is called the "reference change value" (RCV). Arrows to the left and right of your first result show the RCV for this test. For serial results, measurements can be considered different if the second is outside the RCV of the first. Potassium (mmol/L) 95%
Potassium (mmol/L) Normal range Outside normal range Result 2 is within the RCV, so the difference may be due to the combined effects of analytic and biological variation Result 2 is outside the RCV, so the difference is unlikely to be due to the combined effects of analytic and biological variation 4.6 3.3 4.5 3.9 > Result 1 Result 2
The green shaded area represents the reference interval of this test, as provided above. Typically 95% of healthy individuals would be expected to have a test result within this range and 5% of healthy individuals would be expected to have a test result outside this range. Normal range Serial lab results refers to two measurements made over a period of time rather than simply a repeat measurement performed to confirm an initial measurement Measurement timing There is always some uncertainty around the result of any clinical lab test. This kind of variation can be affected by: The defaut values provided here are calculated as described in Appendix 1, and are likely similar in most up-to-date hospital labs. This value can be adjusted if needed, with data from a local laboratory. Analytic variation Pipetting error Reagent deterioration Concentration being measured Calibration drift Human factors When repeated measurements are made over time in an individual, normal physiological processes result in biological variation. Values can be affected by: The values used in this tool are derived from literature at the time of publication, but values can be adjusted if needed in light of further information becoming available. Biologic variation Physiology Diet Activity Stress Mood Weather/climate State of health Living environment The values provided show an example of the normal healthy range for a young adult female. These are provided for rough guidance only and should be replaced by those of your local laboratory as found on the clinical report. Different ranges may apply for patients at different stages of life or with different characteristics, such as: Reference interval Age Gender Ethnicity Age Gender Ethnicity Puberty Pregnancy Menstrual Cycle Menopause The confidence level - the level of probability for differences between readings - is set to 95% by default. This can be adjusted if needed. Confidence level Please enter a number Please enter a number, or leave blank Please enter a number Please enter a number Please enter a number Please enter a number Low value should probably be lower than the high value, no? 99% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 25-hydroxy-Vitamin D Alanine Aminotransferase Albumin Alkaline Phosphatase Aspartate Aminotransferase Calcium Chloride Creatinine Gamma Glutamyltransferase Glucose HbA1c Diabetes IFCC HbA1c Diabetes NGSP HbA1c Healthy IFCC HbA1c Healthy NGSP HDL Cholesterol Hemoglobin Holotranscobalamin Iron Lactate Lactate Dehydrogenase LDL Cholesterol Magnesium Osmolality PCO2 Phosphate Potassium Rheumatoid Factor Sodium Thyroid Stimulating Hormone Total Bilirubin Total Cholesterol Total Protein Total Testosterone Transferrin Triglycerides Urea Uric Acid Vitamin B12 * * * * * Reference change values for HbA1c differ according to whether the patient has diabetes and whether IFCC or NGSP units are used