How to Interpret Lab Reports - Understanding Reference Ranges and Critical Values

Produced by: Science Popularization China

Author: Huang Xiangning, Guangzhou Xinhai Hospital

Supervised by: Guangdong Province Association for Science and Technology

How do the red and green arrows on the test report function? They signify that the test results fall outside the biological reference range, which is commonly referred to as the 'reference range'.

Why might the doctor sometimes state that immediate action is unnecessary, suggesting only regular check-ups, while at other times indicating that treatment is necessary or immediate emergency intervention is required? This depends on the medical diagnosis, the determination of treatment plans, and other physiological evaluations, which often involve relevant concepts such as biological reference ranges, medical decision thresholds, and critical values.

What exactly is a biological reference interval?

A biological reference range is a statistical concept typically derived from a substantial dataset of measurements obtained from normal populations. These measurements are grouped and statistically analyzed according to various factors such as age, gender, and geographical region. The reference range is generally established between the 2.5% and 97.5% percentiles, helping to delineate what is considered normal. Therefore, it is essential to recognize that there might be a portion (5%) of healthy individuals who fall outside this biological reference range.

The reference ranges included on the test report are established based on biological reference intervals. They are generally derived from health industry standards, manufacturer reagent guides, or specialized literature.

For the same test, various laboratories may apply different reference intervals based on the detection systems they utilize.

What does the medical decision-making level signify?

The medical decision level pertains to the concentration of a specific measured component that is crucial for the diagnosis or treatment of a disease during the processes of diagnosis and treatment. This level is typically established through extensive medical practice.

Medical quantitative test results are usually expressed in terms of concentration, while qualitative test results rely on threshold values (cut-off values), indicating positive judgment points.

What qualifies as a critical value?

Critical values are test results that show extremely abnormal findings, which, if not addressed promptly, could endanger the patient's life. Not every test item necessitates the establishment of critical values; different types of hospitals should determine appropriate critical values based on the specific operational characteristics.

There are also significant infectious diseases monitored by the state, such as those classified as critical during the pandemic.

Summary demonstration.

Let’s illustrate using blood sugar as an example (refer to the diagram of blood sugar levels).

The normal upper and lower limits, which constitute the range known as the biological reference interval, correspond to the commonly referenced range found on lab reports. When the fasting blood glucose measurement falls within the reference interval of 3.9 mmol/L to 6.1 mmol/L, the test result is deemed normal.

If fasting blood sugar is below or above the reference range, it may suggest potential health issues, and further diagnosis and treatment should be guided by medical decisions. For example, the diagnostic criteria for diabetes include one of the following conditions: fasting plasma glucose (FPG) greater than or equal to 7.0 millimoles per liter; 2-hour plasma glucose (2h-PG) during an oral glucose tolerance test greater than or equal to 11.1 millimoles per liter; or typical symptoms of diabetes (excessive thirst, excessive eating, frequent urination, and unexplained weight loss) accompanied by a random plasma glucose greater than or equal to 11.1 millimoles per liter.

Glucose serves as a vital source of energy and structural material within the body, maintained in a stable state by various regulatory factors. Blood sugar level acts as a crucial indicator of the sugar content within the body. When fasting blood sugar drops below 2.8 mmol/L, it may lead to hypoglycemic coma; when it surpasses 25.0 mmol/L, hyperglycemic coma, osmotic diuresis coupled with severe dehydration, and ketoacidosis may occur. Thus, establishing critical values can signal that the patient is in a potentially life-threatening situation, and timely and efficient treatment could save the patient's life; otherwise, severe consequences might ensue.

In conclusion, the reference range (biological reference interval) indicated on the test report can assist in evaluating whether the results fall within the normal population range. However, if results exceed this range, there is no need to panic; it is vital to leave professional matters to qualified personnel, as a small number of healthy individuals might also exist outside this reference range. The diagnosis and treatment of illnesses still require doctors to consider medical decision levels and critical values for further evaluation.

Content from: Guangdong Provincial Association for Science and Technology

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