I made this handy reference cheat sheet to augment my understanding of lab values, what they mean, and how to adequately interpret them. In doing so, I was able to make more informed therapeutic recommendations and drug-related intervention. I find it extremely useful to have a copy of this reference in my coat pocket (along with all the sugar goods and snacks). I share this hoping that it will add values to your rotation experience. I am learning and producing the lab reference charts as I progress; thus, you can expect similar charts and discussions in upcoming blog posts. Today I will briefly re-introduce the lab references for BMP (basic metabolic panel), electrolytes, liver, and gastroenterology tests.
While there is no universal lab reference, I find it extremely advantageous to have acquainted myself with at least “ballpark” values. Lab test results can vary depending on test equipment, manufacturer, and analysis procedure/technique. Therefore, the reference values provided on my tables are only comprehensive guidelines for conceptual understanding and application. For more accurate reference values, you should refer to values provided by the laboratory that performs the testing at your assigned institution. Reference values fluctuate based on a number of factors and laboratories are required to validate their reference values annually by the College of American Pathologists (CAP).
Generally, normal lab test results are what we strive for when treating patients but normal lab values does not always commensurate/indicate that the patient is healthy. While lab values are great tools to help us detect health issues and allows for effective therapeutic monitoring, they may not always be straight forward and obvious in certain disease states. For example, lets compare liver test function results in chronic hepatitis and acute hepatitis/cirrhosis. Generally, extremely elevated transaminase level is an indicate for acute hepatocyte necrosis or acute cirrhosis. In contrary, in some chronic hepatitis patients, ALT/AST may appear to be within normal limits (WNL) and/or fluctuates in non-critical value range. This means healthcare provider cannot solely depend on critical analysis of LFTs to identify transient chronic hepatitis, especially if the patient is asymptomatic.
Vise versa, an abnormal lab value does not definitively indicate a condition either. E.g., hypocalcemia normally correlates with low serum calcium (ie. 7.0 mg/L) and naturally, you may recommend adding calcium supplements to offset the diminished calcium value. But is it necessary? Because calcium is primarily protein bound, a decrease or increase in albumin levels can also induce an inaccurate reflection of the true concentration of free calcium in the body. For example, in hypoalbuminemia patients, a calcium correction calculation is crucial!
Example: [Ca]: 7.0 mg/L, [albumin]: 2.0 mg/L
Corrected Ca = [(normal albumin-pt’s albumin) x 0.8] + observed serum Ca level
8.6=[(4-2] x 0.8) + 7.0
[Corrected Ca]: 8.6 mg/L (which is WNL)
Because of the aforementioned issues, it is essential for APPE students to not just exclusively memorize reference ranges but also to recognize the different interfering factors that may affect the results.
Adult lab references in the pipeline:
- cardiac markers
- thyroid functions
- seriotologic tests
- blood gases
- hematologic tests
Feature photo credit: source: http://www.labtestsonline.org.au/understanding/test-accuracy-and-reliability/reference-ranges-and-what-they-mean
- LE, Hoa. “Clinical Laboratory Monitoring”. 2015. Powerpoint Presentation.