Test panels (sometimes called profiles) are typically composed of individual laboratory tests which are related in some way: by the medical condition they are intended to help diagnose (cardiac risk panel), by the specimen type (complete blood count, CBC), by the tests most frequently requested by users (comprehensive chemistry profile), by the methodology employed in the test (viral panel by polymerase chain reaction), or by the types of components included (urine drug screen).
Another disadvantage is the fact that approximately 5% of the test results can be expected to fall outside the normal (bell curve) range for purely statistical reasons.
The proportion of such apparently abnormal results may be even higher if the normal ranges printed on the report do not accurately reflect the species, gender or age of the patient.
It is common for normal ranges for bodily fluid constituents to differ from the general population for very young or old patients, and in some cases (such as hormones) for males versus females.
The statistical considerations typically do not apply for qualitative (present or absent) tests, such as drug screens, unless the substance being tested for (e.g. drug) is actually present at a concentration near the cutoff concentration.