Required section · Section 5 of 6
Three panels: validate the calculation, find the one that does not belong
Three panels arrive for review before release. Panel A: TC 198 mg/dL, HDL-C 58 mg/dL, TG 90 mg/dL. Panel B is the guided case already worked above: TC 210 mg/dL, HDL-C 42 mg/dL, TG 220 mg/dL, calculated LDL-C 124 mg/dL. Panel C: TC 260 mg/dL, HDL-C 38 mg/dL, TG 520 mg/dL, with a Friedewald-calculated LDL-C of 118 mg/dL already sitting in the queue awaiting release.
Work Panel A the same way as the guided case: VLDL-C estimate = 90/5 = 18 mg/dL; LDL-C = 198 - 58 - 18 = 122 mg/dL; non-HDL-C = 198 - 58 = 140 mg/dL. TG is well below the 400 mg/dL ceiling, non-HDL-C (140) is greater than LDL-C (122), and both calculations pass the consistency check. This panel is reportable as calculated.
Panel C is the one that does not belong. Its TG of 520 mg/dL is above the 400 mg/dL Friedewald validity ceiling, which means the LDL-C of 118 mg/dL already computed for it should not have been calculated with that equation and should not be released as a number. Non-HDL-C for Panel C, 260 - 38 = 222 mg/dL, has no triglyceride term and remains calculable and reportable even though the calculated LDL-C does not. The bounded laboratory action is to suppress or flag the calculated LDL-C as not reportable by this equation, report non-HDL-C as calculated, and follow local policy on whether to reflex to a direct LDL-C method if one is validated at the laboratory.
The task is recognizing which of several superficially similar calculated results is the one where the underlying equation's assumption has failed, and stating the laboratory action in bounded terms, without reaching into a treatment decision that belongs to the ordering clinician.
A calculated result that arrives without triggering the TG-ceiling check is a laboratory process gap, not a clinical finding, and it needs to be caught before release, not after.
Illustrative drawing — this picture was drawn rather than captured.
| Panel | TC (mg/dL) | HDL-C (mg/dL) | TG (mg/dL) | Calculated LDL-C (mg/dL) | Non-HDL-C (mg/dL) | Disposition |
|---|---|---|---|---|---|---|
| A | 198 | 58 | 90 | 122 | 140 | Reportable; TG below ceiling, consistency check passes |
| B (guided case) | 210 | 42 | 220 | 124 | 168 | Reportable; TG below ceiling, consistency check passes |
| C | 260 | 38 | 520 | 118 (as calculated) | 222 | LDL-C not reportable by Friedewald; TG exceeds 400 ceiling. Non-HDL-C remains reportable. |
Ordering exercise
Panel C's triglyceride result (520 mg/dL) has just posted. Put the laboratory's review steps in the correct order before the panel is released.
1. Release the panel with the calculation method identified
Report the measured analytes and non-HDL-C, note that LDL-C was not calculated and why, and identify the equation applied.
2. Calculate and verify non-HDL-C
Non-HDL-C has no TG term, so calculate TC - HDL-C (222 mg/dL) and confirm it is still a valid, releasable result.
3. Suppress or flag the calculated LDL-C
Because TG exceeds the Friedewald ceiling, mark the calculated LDL-C as not reportable by that equation rather than releasing the number as-is.
4. Compare TG to the equation's validity ceiling
Check the measured TG (520 mg/dL) against the laboratory's chosen equation's validated range before trusting any calculated LDL-C already in the queue.
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