---
title: "Module 5. Interpreting the Metric Levey-Jennings Graph"
description: "![](https://bostoncellstandards.com/wp-content/uploads/2026/09/levey-jennings-graph-1-1024x492-1.webp) *Figure 5. Metric Levey-Jennings Graph With Explanations*   A Levey-Jennings Graph tracks quality control results over time against your expected mean and ranges for QC data acceptability. If your control results fall outside these pre-defined ranges, it typically requires…"
url: "https://bostoncellstandards.com/learning-center/documentation/metric-spc-tutorial/interpreting-the-metric-levey-jennings-graph/"
updated: "2026-09-01"
category: Metric SPC Tutorial
---

# Module 5. Interpreting the Metric Levey-Jennings Graph

![](https://bostoncellstandards.com/wp-content/uploads/2026/09/levey-jennings-graph-1-1024x492-1.webp)

*Figure 5. Metric Levey-Jennings Graph With Explanations*

 

A Levey-Jennings Graph tracks quality control results over time against your expected mean and ranges for QC data acceptability. If your control results fall outside these pre-defined ranges, it typically requires a prompt evaluation to determine whether the IHC assay was valid.

**Key Clinical & Regulatory Considerations:**

- **Direction of Errors:** Most out-of-range events in IHC will be aberrantly *low*, indicating a loss of assay sensitivity. When this happens, the lab must resolve the issue and determine if patient sample staining might be affected.
- **Regulatory Documentation:** Documentation of an out-of-range event and its subsequent resolution is typically required by regulatory authorities. (*Note: You can use Metric's "Edit" button on the QC Data table to add resolution comments and maintain your audit records*).
- **Westgard Rules:** Further information about Levey-Jennings graphs and the application of Westgard rules can be found in numerous Journal review articles, textbooks, and the Westgard website: [https://www.westgard.com/](https://www.westgard.com/)

When reviewing your Levey-Jennings graphs in Metric, you are generally looking for three categories of quantitative errors. Recognizing these patterns offers clues as to the root cause of an assay issue.

## Common Levey-Jennings Graph Patterns

### Pattern 1: Drift

Drift appears as a consistent trend on the graph that develops slowly over days or weeks, often only coming to your attention when it finally crosses the 2 SD or 3 SD limits. Something is changing slowly in the instrument or reagents. See Figure 6 below.

 ![](https://bostoncellstandards.com/wp-content/uploads/2026/09/Screenshot-2026-07-28-102259-1024x376.png)

*Figure 6. SPC Error - Drift Pattern*

###### Possible Causes:

- Slow reagent degradation (approaching end of life).
- An instrument slowly failing.
- The control itself is deteriorating.

### Pattern 2: Sporadic Outlier

This pattern is a single, sudden out-of-range event. A significant malfunction of some sort has happened, which usually requires repeating the test. Notice how this pattern differs visually from the gradual drift pattern as shown in Figure 6.

 ![](https://bostoncellstandards.com/wp-content/uploads/2026/09/Screenshot-2026-07-28-102453.png)

*Figure 7. SPC Error – Sporadic Outlier Pattern*

###### **Possible Causes:**

- Failure to properly dispense onto the slide.
- Pump malfunction.
- Heater failure.
- Drying of the reagent on the slide.

### Pattern 3: Shifts

This pattern shows a significant shift in QC levels to a new stable level. See Figure 8 below.

 ![](https://bostoncellstandards.com/wp-content/uploads/2026/09/Screenshot-2026-07-28-102646-1024x376.png)

*Figure 8. SPC Error – Shifts*

###### **Possible Causes:**

- Reagent lot change
- Instrument maintenance