Laboratory tests have become routine. Not only do doctors order lab tests, often patients or even otherwise healthy people get them done of their own accord. What is important is how we interpret these reports.
Often the results of the tests are interpreted in relation to the normal reference range mentioned alongside, whether the values are within the reference range “normal” or fall outside it “abnormal”. Labs usually have their own reference range.
Generally, we tend to give too much weight to a normal result and are reassured by it. But, here it is important to keep in mind the fact that a normal result is just a picture at that point of time. It can change.
And, what is equally important is that instead of looking at a single test result, one should look for trends in the results. Always compare the results of a particular test with previous reports even when a result is normal. Results that show change over time i.e. show a rising or declining trend are important and should not be ignored.
Any result which has been in the low normal range for the last many years, but is now in the high normal range even though still normal, should be taken cognizance of and investigated accordingly.
This can be most commonly illustrated by blood sugar. A fasting blood sugar level higher than 126 mg/dL can be diagnosed as diabetes, according to the recommendations of the American Diabetes Association (ADA). Prediabetes is fasting blood sugar ranging between 100 and 125 mg/dL. If your patient usually has had his blood sugar around 80, but in the latest report, the blood sugar is now, say 98 or 106. This is still not higher than the diagnostic cut-off. But, this is the time, when you can advise lifestyle modifications to your patient – a healthy diet, increasing physical activity, quitting smoking etc. This will keep the blood sugar in check and prevent progression to prediabetes or even full blown type 2 diabetes.
Another example is thyroid stimulating hormone (TSH). The normal range is between 1.0 and 4.0. A TSH value greater than 2.5 indicates a risk of hypothyroidism and a value of 4.0 is an indicator of mild hypothyroidism.
PSA velocity is another important test in prostate cancer screening. It is the change in the level of prostate specific antigen (PSA) over time. It has been shown that PSA elevations can precede clinical disease by 5 to 10 years. PSA velocity greater than 0.75 ng/mL per year indicates a higher risk of a diagnosis of prostate cancer than the actual PSA level itself.
Liver chemistry, kidney function tests, electrolytes, lipid profiles, reticulocyte count, SGOT/SGPT ratio are some tests, which should be interpreted carefully, taking into consideration the previous reports, before labeling them as normal.
An example of declining trend is hemoglobin. If the hemoglobin has been slowly decreasing, but within the normal range, then evaluate the patient for the cause of anemia.
In dengue patients, more than the falling platelet count, it is the "rapidity" of fall in platelet count, which is significant. A rapid fall of platelets is a warning sign of impending severe dengue.
Be alert to changing trends in lab results even if within normal limits. Take note of the family history. Repeat the test and/or investigate your patient further. This is how diseases can be diagnosed early and treated timely.
Dr KK Aggarwal
National President IMA & HCFI