Welcome to the Daily Apple, a new page on Your Health Forum that addresses questions that you may be curious about and are likely to come up in clinic visits. The goal is to answer questions in a useful format to allow quick learning and application in an article about 500 words or less.
What do normal lab tests mean?
Quick Answer: Not enough to tell you whether you are healthy or not
Table of Contents
Introduction: What does normal mean?
A common question that comes up is related to the significance of normal bloodwork. Clinicians often order bloodwork as part of a comprehensive assessment. The tests include cholesterol, electrolytes, kidney, liver function, and blood count. The results indicate how the body is functioning as a way of providing input on directing health needs.
The results compare to parameters set using a standard deviation curve, or bell-shaped curve, with normal falling within a particular range, usually within 95% of the curve.
The bell-shaped curve is a statistical calculation that captures where the majority of results would fall. The measures require two elements: a mean, which is calculated by totaling up all the results and dividing the total by the number of results, and a standard deviation, which considers the distance of each result from the calculated mean. Usually, the normal range is within two standard deviations above and below the mean (95% of curve.) See the example of a standard curve in the figure below.
When you are given results and told that everything is “normal,” it simply means that your results fall within a normal distribution range.
What Normal Bloodwork Doesn’t Tell You
The concern that you have is not driven by a physical process.
Normal bloodwork does not mean that you and your doctor can stop looking for a source for your concerns. If you are dealing with a health complaint, for instance, abdominal pain, normal bloodwork does not mean the search is over. Clinicians use multiple modalities, including an excellent history and physical examination, general and specific bloodwork, ultrasound, and radiographic imaging to piece together a cause. They can use other tests, including ones that assess functions (e.g., nerve conduction studies, ECHO, Stress test, sleep studies.)
Studies indicate that 70 to 90% of medical diagnoses come after a careful, comprehensive history (1). A “history of chief complaint” is conducted by asking open-ended questions and following up with targeted questions. The provider must solicit the patient’s chief complaint and underlying motive for the visit without interruption and cue into these statements. A visit without interruption is relatively uncommon, with one report of 74 office visits showing that in only 17 (23%) visits was the patient given a chance to state the reasons for the concerns or “opening statement.” The majority (69%) of visits came with interruption of the patient’s statement (2). Interestingly the study was published in 1984. One can imagine a higher frequency of disruption in the electronic medical record era.
While we would like to be reassured by normal results, they are not always helpful. Tests have varying sensitivities and specificities, which can sometimes miss a disease process. Additionally, a process may be developing outside the limits of sensitivity of the history, physical, laboratory studies, and sometimes even imaging studies. It is essential to see the bloodwork as a snapshot of your health – one that may require repeating to capture the change. Someone who is actively bleeding may have normal blood counts. The point is to go back to the history and observations and no rely on normal tests.
A productive provider-patient partnership includes follow-up visits and a review of progress.
You are healthy enough.
Normal bloodwork does not mean normal health or that you are “healthy enough.” Although the results are specific to the test, sometimes there may be results that fall in the “normal” range but are significant enough to cause changes in the body.
One example of this is the Hemoglobin A1c or glycosylated hemoglobin. This test indicates the levels of glucose present in the blood (it is a measure of sugar complexes on hemoglobin) over three months. This result is one of the gold standards in diagnosing diabetes. However, this result can vary based on various diseases, e.g., chronic kidney disease, and give a falsely normal level. Additionally, findings of high glucose, such as peripheral neuropathy, can be seen at lower levels than what is considered the range of diabetes (A1c >6.5).
Additionally, interest in determining what “normal” is drives research on other tests like the thyroid-stimulating hormone (TSH). A high-normal TSH (4-5 mIU/L, 97.5th percentile) may not identify people who could develop hypothyroidism. These results have important implications for a condition known as subclinical hypothyroidism, which 4 to 20% of adults have.
An average cholesterol level does not mean much too. One study in 2000 looking at cholesterol levels in 1,206 men and women hospitalized for heart disease showed that 50% of those who needed bypass surgery had normal cholesterol levels.
Yes, sometimes, a normal test is not the best indicator of health and disease. I like to check studies which I call functional tests of metabolism. This includes triglycerides after a meal (not fasting) and an inflammatory score, a blood test of multiple components indicating liver inflammation. Measurements of weight/height (BMI), waist circumference, and neck circumference also have value.
|Lab Test||Normal Result|
|ALT||Less than 45 U/L|
|AST||Less than 45 U/L|
|Bilirubin, total||Less than 1.3 mg/dL|
|Creatinine, serum||0.6 – 6 mg/dL|
|White blood count||4.0 – 10.2 wbc/mm3|
|Glucose, plasma||70-110 mg/dL|
|Potassium, serum||3.5-5.3 mmol/L|
|Sodium, serum||134-147 mmol/L|
|Chloride, serum||96-109 mmol/L|
|Uric acid||3.9-9 mg/dl (male); 2.2-7.7 (female)|
|Triglycerides||Less than 150 mg/dL|
|Thyroid stimulating hormone (TSH)||0.5 to 5.0 mIU/L|
|HbA1c (diabetes screen)||4 – 5.6%; 5.7-6.4 prediabetes, 6.5 diabetes|
So, the short answer is not much! There is a lot more in determining health and the cause of a concern than bloodwork.
Stay-tuned for more Daily Apples to come. Thanks for reading this. If you have found it useful
Sanders L. Every Patient Tells a Story. New York: Broadway Books; 2009:6–91.
Beckman HB, Frankel RM. The effect of physician behavior on the collection of data. Ann Intern Med. 1984 Nov; 101(5):692-6. doi:10.7326/0003-4819-101-5-692.
Dr. Christopher Cirino
Founder of Your Health Forum