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
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