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Tests of Limited Value

“Conventional wisdom holds that about 20 to 50 percent of the lab testing that is done is unnecessary, especially high-volume automated testing." (Kent Lewandrowski, MD*).
There are many tests that are not obsolete but are often over-utilized.
The table below contains some examples of tests that are over-ordered, over-interpreted, or simply unneeded much of the time.

Test of Limited Value
7-10% of the population will have a positive ANA screen yet few of these people are sick. The ANA is useful in the hands of a rheumatologist, but often leads clinicians down unneeded paths (working up everyone with a positive ANA titer for lupus is not good medicine).
CBC with manual differential
A CBC without differential or with an automated differential is all that is needed the vast majority of time. A manual differential is not only less accurate than an automated differential (counting 10,000 cells is better than counting 100), it requires a significant amount of tech time.
Studies show that troponin assays can replace CK-MB in all settings. Many cardiologists wish to preserve their 'comfort level' of using CK-MB to gauge reperfusion injuries but troponin can serve this role as well.
C-reactive protein (CRP)
The within-patient variation for CRP makes trending values almost pointless. This test has a limited role in some cases (such as sepsis) but it is often over-ordered for routine inflammation workups.
Erythrocyte sedimentation rate (ESR)
ESR has some value in the workup of temporal arthritis but generally is of limited value.
Folate is essential for fetal development but our foods are now well fortified with folate. Measuring it routinely rarely makes sense since deficiencies are not common. True B12/folate deficiencies are better tested using methylmalonic acid (MMA) and homocysteine.
Ionized calcium (iCa)
iCa tends to run low in patients who are very ill, so physicians will often give these patients IV calcium, yet there’s no strong evidence to support replacing calcium in critically ill patients.
Lactate dehydrogenase (LD)
LD is abnormal in patients with hepatocellular disease and a variety of other conditions but usually other tests such as liver enzymes and bilirubin are more specific.
Novel cardiovascular risk markers (eg, hsCRP, LP(a), LpPLA2)
There are literally dozens of cardiovascular risk markers which have been proven to help predict patient risk for a future cardiac event. However these novel risk markers don't add significant value over the standard LDL, HDL, and triglyceride tests. Novel risk markers may identify risk for some special patient populations but in general, they do not add much and are costly.
Ova and parasites
Ova and parasite testing is usually not needed in the routine work-up of diarrhea.
Prothrombin time (PT) and partial thromboplastin time (PTT) ordered pre-surgery
If there is no history of a coagulopathy, this pre-surgery testing is generally not needed.
PSA in men >75-years-old
Most men die with prostate cancer, not from prostate cancer. Screening older men can lead to subjecting them to unneeded biopsies and treatment for slow-growing tumors.
Vitamin D (vit-D)
Although it is true that many in the US have deficiencies of vit-D, measuring it is often unneeded. Simply telling patients to take a vit-D supplement or spend more time outdoors is generally all that is needed.

These are just a few examples of tests that have value, but are often ordered in a context in which they provide little actual value to the patient and clinician. Having the UM team work on these types of issues can be very engaging and rewarding.