Normal and Referance Range

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1. Normal & Reference range

2. Introduction The reference range is also termed the reference interval. DEFINATION which is defined by reference limits and obtained from measurements on the reference population for a particular test OR A pair of medical decision points that span the limits of results expected for a given condition. OR When making any clinical measurement, for example weighing a patient or measuring pulse rate, results are interpreted by reference to what is normal.

3. What is Reference range Reference range include all the data points that define the range of observations (e.g., if the interval is 5–10, a patient result of 5 would be considered within the interval ). The upper and lower reference limits are set to define a specified percentage (usually 95%) of the values for a population; this means that a percentage ( usually 5 %) of patients will fall outside of the reference interval in the absence of any condition or disease. Laboratory test data are used to make medical diagnoses, assess physiologic function, and manage therapy. When interpreting laboratory data, clinicians compare the measured test result from a patient with a reference interval. Reference intervals are sometimes erroneously called “normal ranges.” While all normal ranges are in fact reference intervals, not all reference intervals are normal ranges .

4. Why establishing a reference interval: A reference interval is established when there is no existing analyte or methodology in the clinical or reference laboratory with which to conduct comparative studies.

5. To establish a reference range study: Define an appropriate list of biological variations and analytic interferences from medical literature. Choose selection and partition (e.g., age or gender ) criteria . Complete a written consent form and questionnaire to capture selection criteria. Categorize the potential reference individuals based on the questionnaire findings. Exclude individuals from the reference sample group based on exclusion criteria .

6. Define the number of reference individuals in consideration of desired confidence limits and statistical accuracy. Standardize collection and analysis of reference specimens for the measurement of a given analyte consistent with the routine practice of patients Inspect the reference value data and prepare a histogram to evaluate the distribution of data. Identify possible data errors and/or outliers and then analyze the reference values. Document all of the previously mentioned steps and procedures.

7. What is normal range ? Normal range choice between defining an ‘ideal state’ or determining an ‘average’ state considered normal range more practical to analyze ‘average’ state with respect to a biological parameter results in a symmetric (Gaussian) distribution a normal range is the range in concentration of 95% of the normal (healthy) population.

8. Factors that affect the reference range Various quite normal physiological factors may need to be taken into account when interpreting laboratory test results. Test results may be affected by: • Age of the patient. • Sex of the patient. • Pregnancy. • Time of the day the sample was collected.

9. For example, blood urea concentration rises with age and blood hormone levels are different among adult males compared with adult females. Pregnancy can affect the results of laboratory tests of thyroid function. Blood glucose levels fluctuate throughout the day . Alcohol and many drugs can affect blood test results in a variety of ways.

10. The results of measuring the concentration of hypothetical substance X in the blood of a large population of apparently healthy individuals (the reference population), and those with a hypothetical disease Y . Since the blood concentration of substance X is usually raised in those suffering disease Y, it is used as a blood test to confirm the diagnosis among those with symptoms of Y. From the graph it can be seen that the concentration of X among apparently healthy individuals ranges from 0.3 to 8.0 mmol /L

11. Reference interval use can be grouped into three main categories : diagnosis of a disease or condition monitoring of a physiologic condition therapeutic management

12. diagnosis of a disease or condition

13. monitoring of a physiologic condition

14. THERAPEUTIC RANGE It is the concentration range of drug in plasma where the drug has been shown to be efficacious without causing toxic effects in most people.

15. Referance range of routne biochemistry parameter

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