Verify, call, read back, document and escalate a critical value, and correct a released result.
Why it matters
Some results mean a patient is in danger right now: a potassium high enough to stop the heart, a glucose low enough to cause a seizure, a positive blood culture in a newborn. These are critical values (sometimes called panic values). The lab's job does not end when the number is on screen. It ends when a responsible caregiver has received, understood and acknowledged the result, and that is documented. Delayed or failed critical-value calls are a recognized cause of patient harm, and accreditors inspect this process closely.
Scope. The critical limits below are illustrative teaching values only. Every lab's medical director and medical staff approve the lab's own list, which you follow. The activity is a paper role-play with fictional patients. Nothing here is medical advice.
The core idea
A critical-value process has five parts:
- A written list. Tests and limits, approved by the lab director with the medical staff, sometimes with different limits for newborns or for repeat results.
- Verification, without delay. Check that the specimen is acceptable (no hemolysis, clot or contamination pattern), the instrument QC is in control, and the result fits the patient history. Some labs repeat the test; others do not, because a repeat delays the call. Follow policy.
- Notification within a set time. Call the responsible licensed caregiver (the ordering provider or the patient's nurse, as the policy defines) within the lab's time limit, often expressed in minutes.
- Read-back. The receiver repeats the patient's name, second identifier, test and value back to the caller. This catches mishearing ("fifteen" vs "fifty").
- Documentation. In the laboratory information system (LIS): who was called, their name and role, date and time, the value, and that read-back was completed.
If the caregiver cannot be reached within the time limit, the lab follows an escalation path: for example the charge nurse, then the covering provider, then the lab medical director.
An illustrative critical list
| Test | Low | High |
|---|---|---|
| Potassium | below 2.8 mmol/L | above 6.2 mmol/L |
| Glucose | below 50 mg/dL | above 450 mg/dL |
| Sodium | below 120 mmol/L | above 160 mmol/L |
| Hemoglobin | below 7.0 g/dL | above 20 g/dL |
| Platelets | below 20 x10^9/L | above 1000 x10^9/L |
| Positive blood culture Gram stain | any |
(Illustrative only. Real lists differ between labs and patient groups.)
Worked example: a call, start to finish
At 02:14 the analyser reports potassium 6.9 mmol/L for a fictional inpatient, Sam Ortiz (MRN 40417). The MLS:
- Checks the specimen: no hemolysis flag, plasma looks normal, no EDTA pattern (calcium normal). QC from 01:30 is in control. The previous potassium was 6.0 yesterday, and creatinine is high, so the result is plausible.
- Calls the patient's unit at 02:17 and asks for the nurse caring for Sam Ortiz.
- Says: "This is the lab with a critical value for Sam Ortiz, MRN 40417. Potassium is 6.9 millimoles per litre, collected at 01:58."
- The nurse reads back: "Sam Ortiz, 40417, potassium 6.9." The MLS confirms.
- Documents in the LIS:
Critical K 6.9 mmol/L called to RN Priya Shah (4 West) 02:19, read back confirmed. Caller: A. Lee, MLS.
Total time from result to documented call: five minutes. If no one had answered by the time limit, the MLS would move to the next person on the escalation path and document each attempt.
Reporting beyond critical values
The post-analytical phase also includes:
- Autoverification: LIS rules release normal results that pass every check (QC in control, no flags, delta check passed) without manual review, so staff can focus on the exceptions.
- Corrected reports: if a released result was wrong, the lab issues a corrected report, notifies the caregiver, and keeps the original visible in the audit trail. Results are never silently overwritten.
- Comments: standard comments ("hemolyzed specimen; potassium may be falsely raised") travel with the result.
Common mistakes
- Leaving a voicemail or message with a clerk instead of speaking to a licensed caregiver.
- Skipping read-back, or documenting "called" without a name and time.
- Delaying the call to repeat a test when policy does not require it.
- Calling a critical value that is clearly an artefact (an EDTA-contaminated potassium) instead of requesting a redraw.
Quick recap
- A critical value demands immediate notification of a responsible caregiver.
- Verify quickly, call within the time limit, require read-back, and document who, when and what.
- Follow the escalation path when the caregiver cannot be reached.
- Corrected reports keep the original result visible in the audit trail.
Try it
Open the Do tab. You will role-play a critical call on paper and write the documentation.