MV Basics Series
In a laboratory, not all tests are conducted the same. Some simply tell us yes or no, while others provide exact numbers that guide critical medical decisions. The three main types of laboratory testing - Qualitative, Semi-quantitative and Quantitative - determine how results are applied in real-life patient care.
Understanding the difference among testing methods can help you make better decisions about which method best fits your laboratory needs. Each method is fundamentally different - having its own advantage and disadvantages.
What is Qualitative Testing?
Qualitative testing is conducted to determine the presence or absence of a substance in a sample. This provides a simple yes or no answer. For instance, a pregnancy kit detects the presence of human chorionic gonadotropin (hCG) levels in the blood or urine indicated by a simple color change. A negative result means the substance is absent. A positive result means the substance is present but does not quantify the amount of hCG.
The most common application of qualitative testing in Method Verification is the Limit of Detection (LoD) experiment. This experiment is designed to determine the smallest amount of analyte a method can confidently detect, without having to quantify the analyte concentration.
Qualitative testing is useful when a laboratory needs to determine whether an analyte is present, without the need to measure its exact concentration. This offers quickest and most cost-effective approach, making it especially useful in situations where speed and efficiency are key.
However, qualitative testing has its own limitations in clinical use. This cannot provide information about the amount of substance present nor can it distinguish between different types of substances being tested in a sample, making it of limited value for clinical decision making.
What is Semi-Quantitative Testing?
Semi-quantitative is performed when approximate numerical or categorized intervals such as "1+", "2+", or "High" are sufficient and the exact analyte concentration is not needed. It bridges the gap between purely qualitative yes or no and quantitative testing.
Chemical examination for urine in clinical microscopy is a classic example for semi-quantitative testing. Instead of performing a full quantitative analysis for each analyte, a technician uses a dipstick to quickly screen for key markers such as glucose, protein, and ketones. The color change on each pad of the strip corresponds to an approximate concentration, which is then reported as a semi-quantitative result like "trace," "1+," "2+," or "3+.
Semi-quantitative methods are best useful when an exact analyte is not necessary for clinical decision making, eliminating the need for time-consuming precise measurements. However, due to results being less specific, approximate concentrations may lead to misinterpretations in settings where exact values are critical. Additionally, many semi-quantitative tests rely on visual interpretation such as comparing color intensities on a test strip, making it prone to human error.
What is Quantitative Testing?
Quantitative testing is used to measure the exact concentration of a substance in a sample. This provides numerical results which are expressed in different units. In a similar example above, quantitative pregnancy test measures the specific levels of hCG hormone in the blood expressed as milli-international units per milliliter (mIU/mL). This is used to determine the exact age of the fetus, unlike qualitative which only determines the presence of the fetus.
Common examples of tests which rely on quantitative methods are those performed under blood chemistry, such as blood cholesterol measurement. By providing measurable values, these results reflect a patient’s health status therefore allowing clinicians to compare test results against established normal values and determine severity of a medical condition.
Although quantitative testing requires complex technologies and is much more expensive, this type of testing provides the most accurate and precise result among the three types. It can provide detailed information about the analyte, making it is useful in clinical decision making.
Qualitative vs Semi-Quantitative vs Quantitative: Which Fits the Need?
The decision to use qualitative, quantitative or semi-quantitative testing depends on the purpose and goals of the test:
Qualitative testing is useful when you need a quick and simple answer about the presence or absence of the analyte, but the concentration of the substance is not important. Opt for semi-quantitative testing when an approximate idea of the concentration is needed, but not the exact value. And lastly, opt for quantitative testing when detailed information about the analyte concentration is needed, providing a numerical value that’s essential for clinical decision making.
In some cases, both qualitative and quantitative testing may be used together. Qualitative methods are frequently used as initial screening tests to determine the presence of a disease. A follow-up confirmation test using quantitative method is then performed to verify the presence of the disease and its extent. The presence of COVID antigen as a qualitative test provides an effective detection mechanism. Quantitative measurement of COVID would be best for measuring treatment effectiveness.
Qualitative | Semi-Quantitative | Qualitative | |
Purpose | Determines the presence or absence of the analyte | Determines the approximate range of the analyte | Determines the exact concentration of the analyte |
Result Type | Positive/Negative ; Detected/Not Detected | Intervals (Trace, Low, Medium, High) or numeric ranges (1+, 2+, 3+) | Numerical value expressed in units (100 mg/dL) |
Real-life Lab Examples | hCG rapid pregnancy test | Urine dipstick protein | Blood cholesterol test |
Advantages | Fast, simple, cost-effective and no need for advanced analyzers | Provides more information than qualitative alone | Highly accurate and precise, useful for diagnosis and treatment |
Disadvantages | Limited use for clinical interpretation | Less precise than quantitative, results often subjective (urine dipstick color change) | Requires advanced analyzers and trained personnel, more expensive |
Think you’ve mastered the key differences between Qualitative, Semi-Quantitative and Quantitative Testing? Test your knowledge with our interactive quiz here!
Resources
Westgard, James. (2020). Basic Method Validation, 4th Edition. Wisconsin, Westgard QC, Inc.
Brennan, J. (2018, March). Quantitative Vs. Qualitative Data and Laboratory Testing. Sciencing. Retrieved from: https://sciencing.com/quantitative-qualitative-data-laboratory-testing-8433446.html
The FullStory Education Team Experts. (2021, October). Qualitative vs. quantitative data: what's the difference?. FullStory Blog. Retrieved from: https://www.fullstory.com/blog/qualitative-vs-quantitative-data/#:~:text=Quantitative data is numbers-based,what happened behind certain behaviors.
International Organization for Standardization. (2017). ISO 17025:2017 - General requirements for the competence of testing and calibration laboratories. https://www.iso.org/standard/66912.html
Erasmus, R. T., & Zemlin, A. E. (2009). Clinical audit in the laboratory. Journal of Clinical Pathology, 62(7), 593-597. https://doi.org/10.1136/jcp.2008.061515
Peters, F. T., Drummer, O. H., & Musshoff, F. (2007). Validation of new methods. Forensic Science International, 165(2-3), 216-224. https://doi.org/10.1016/j.forsciint.2006.05.021
Baruch, H.R., Hassan, W., Mehta, S. (2018). Eight Steps to Method Validation in a Clinical Diagnostic Laboratory. American Society for Clinical Laboratory Science, 32(4), DOI: https://doi.org/10.29074/ascls.118.000307
McPolin, Oona. (2016). Replicates in Analytical Methods - When and How Many?. Mourne Training Services. Retrieved from: https://mournetrainingservices.com/replicates-in-analytical-methods-when-and-how-many/#comments