In clinical laboratories, quality control (QC) and patient safety are paramount. Among the various internal QC tools, DELTA CHECKS have emerged as a powerful strategy to detect significant changes in a patient's test results over time. But are they truly essential, or just another redundant alert in a sea of laboratory data? Based on both literature and real-world laboratory experience, this article explores the value and application of delta checks.
What is a Delta Check?
A delta check compares a current test result with a previous result from the same patient. If the change exceeds a defined threshold, it flags a warning for review. For example, a sudden hemoglobin drops from 14 g/dL to 8 g/dL overnight in a non-bleeding patient would trigger a delta check alert. Delta checks are not error detectors by themselves; they are indicators of possible error, acute physiological change, or both.
Need for Delta Checks
Delta checks play a crucial role in ensuring laboratory accuracy and patient safety. They help identify both pre-analytical and analytical errors that might otherwise go unnoticed. For instance, in one case, a flagged potassium value led to the detection of haemolysis that was missed by the haemolysis index. In another, a sudden spike in LDH was traced back to delayed centrifugation, while consistent drops in albumin levels uncovered a calibration drift due to pipetting malfunction. Beyond error detection, delta checks can highlight true clinical deterioration, such as a sudden drop in haemoglobin indicating internal bleeding. In high-throughput laboratories, where automation minimizes manual errors, delta checks serve as a secondary safeguard. They are especially valuable during understaffed shifts, helping technicians prioritize critical samples and maintain quality control. In understaffed shifts (as many labs experience), delta checks become crucial QC flags that help technicians prioritize samples needing attention.
Challenges and Limitations
While delta checks provide valuable quality control, they have certain limitations. They are ineffective for first-time patients as there are no prior results for comparison. Poorly defined thresholds can either trigger excessive false alerts or miss genuine errors. Additionally, their effectiveness depends heavily on the capabilities and correct configuration of the Laboratory Information System (LIS), any misconfiguration can lead to missed alerts or unnecessary alarm fatigue.
When They Helped: A Personal Anecdote
A delta check flagged an abrupt rise in total bilirubin from 2.3 mg/dL to 14.8 mg/dL overnight. Investigation revealed acute bile duct obstruction due to gallstone migration, and the patient was immediately taken for endoscopic intervention.
An unexpected increase in urea from 46 mg/dL to 138 mg/dL in 18 hours was detected by the delta system. This triggered urgent nephrology review, which diagnosed rapidly progressing renal failure due to drug-induced nephrotoxicity.
In one ICU case, troponin I rose sharply from 0.02 ng/mL to 2.4 ng/mL within hours. Although not part of routine delta checks, manual review based on trends led to identification of a silent myocardial infarction in a sedated patient.
In another instance, a glucose result of 52 mg/dL in a known diabetic patient raised a delta flag. On checking, we realized the sample had been drawn from a line through which insulin had recently been infused. A redraw confirmed the actual glucose was 164 mg/dL.
Conclusion
So, is there really a need for delta checks? The answer is a resounding YES, provided they are used wisely. Delta checks are not just numbers they are stories, alerts, and sometimes the silent voice of a patient in distress. They bridge past and present, turning data into insight.
As a laboratory professional, I believe delta checks are not optional extras but essential safeguards—like seat belts in diagnostic driving. They may not prevent the crash, but they often reduce the damage.