Quantitative results should be reported below the detection limit

January 27, 2013


To recall:

LoB = limit of blank
LoD = limit of detection
LoQ = limit of quantification

Although there are various ways to calculate these quantities, LoB can be estimated by running some samples without analyte and adding 2 sd to the average. LoD is estimated by running some low samples and adding 2 sd to the LoB. LoQ is estimated by running some low samples and calling LoQ where the data equals a pre specified CV. See here for some pictures.

I’m not sure how most laboratories handle reporting values below the detection limit (LoD) but CLSI EP17-A2 suggests that for values between the LoB and LoQ, the value should be reported as “analyte detected, result < LoQ.”

Some of my blog entries (such as this one) come from my consulting experience, which is of course confidential. So here is a made up example of a tumor marker with a detection limit of 1.0 and some patients who are being serially monitored. As one might expect, no tumor marker is an ideal result.

Patient A: 0.3, 0.6, 0.2, 0.6, 0.3
Patient B: 0.2, 0.5, 0.4 0.6, 0.8

These quantitative results could be compared to the reports for all values of “analyte detected, result < LoQ.”

Clearly, there is something happening with patient B and this trend information is lost by the reporting rules.

Taking away the challenge – or the good old days

January 13, 2013


I attended an aviation club where a video was shown which depicts a fly-by-wire system for general aviation. The benefit of such a system is that a stall or unusual attitude is eliminated. The reception to the video was varied with some doubting that it would improve safety but one comment that caught my attention was that this advance removes the challenge of flying.

But progress is inevitable – here is a table of progress for general aviation planes, starting with the introduction of the aileron. So if you really wanted to go back to the old days, you would turn by warping the wing. Some pilots might enjoy the challenge of flying legacy (steam) gauges in a tail wheel plane without an autopilot in IMC but I would rather have all of the latest technology.

Original Item Revision Benefit
Warped wing Aileron Easier to turn
Carburetor Fuel injection No ice build up
Hand flying Auto pilot Relieves pilot workload
Legacy gauges Glass cockpit More information
Hand Flying Straight and level button Easier recovery from unusual attitudes
Tail wheel Tricycle Easier to land
No fly by wire Airbus style fly by wire* Can’t put plane in unusual attitude
No BRS BRS (parachute) Safer

*Not yet available for general aviation