Clinical Chemistry & In-House Analyzer Quality Control

Clinical Chemistry & In-House Analyzer Quality Control

Why In-House Chemistry Matters

Veterinary practices rely on in-house chemistry analyzers to produce serum chemistry panels within minutes, allowing the supervising veterinarian to make treatment decisions during the same appointment. As a veterinary assistant or technician, you are responsible for collecting a quality sample, operating the analyzer correctly, performing quality-control (QC) checks, and flagging abnormal values for the veterinarian's interpretation. Errors at any step can lead to incorrect diagnoses and patient harm.

Step 1 — Collecting and Processing the Sample

Most in-house chemistry analyzers require serum. Blood is collected into a serum separator tube (SST), which contains a clot activator and a gel barrier. Allow the tube to clot at room temperature for the time specified by the tube manufacturer (typically 30 minutes for most species), then centrifuge at the speed and duration recommended by your laboratory protocol. The gel migrates during centrifugation to form a physical barrier between the clot and the serum.

Avoiding hemolysis is critical. Hemolysis — the rupture of red blood cells — releases intracellular contents into the serum and falsely alters many analyte values, particularly potassium, ALT, and LDH. Common causes include using a needle that is too small, excessive vacuum, vigorous mixing, or delayed centrifugation. After centrifugation, inspect the serum layer: clear to pale yellow is acceptable; pink or red indicates hemolysis and must be reported to the supervising veterinarian before proceeding, because results may be unreliable.

Harvest serum by pipette or by carefully decanting above the gel barrier. Load the rotor or cuvette according to the analyzer operator manual — always follow the manufacturer's instructions exactly.

Step 2 — The Chemistry Panel

A standard small-animal chemistry panel includes analytes that reflect the function of several organ systems:

• ALT (alanine aminotransferase) — hepatocellular enzyme; elevated values suggest liver cell damage (dog and cat specific).
• ALP (alkaline phosphatase) — associated with cholestasis and bone; elevated values prompt investigation of liver or bone disease (dogs are particularly sensitive).
• BUN (blood urea nitrogen) — urea produced by the liver, excreted by the kidneys; elevated values suggest renal disease, dehydration, or high dietary protein.
• Creatinine — filtered by the kidneys with minimal tubular influence; elevated values alongside elevated BUN support azotemia.
• Glucose — energy substrate; elevated values suggest diabetes mellitus or stress; decreased values suggest insulinoma, sepsis, or juvenile hypoglycemia.
• Total protein and albumin — produced by the liver; decreased values suggest liver disease, protein-losing nephropathy, or malnutrition.

Record every value on the standardized log sheet immediately. Do not skip a field. Circle any value outside the species reference interval and note the direction (high or low). Always use species-specific reference ranges — feline and canine normal values differ significantly for several analytes.

Step 3 — Quality Control

Quality control is the process of verifying that the analyzer is producing accurate and reproducible results before patient samples are run. Running QC is non-negotiable; patient safety depends on it.

Control sera are commercially prepared samples with a known target value and an acceptable range. Practices typically use two levels — a low control and a high control — to bracket the normal patient range. Run controls according to the schedule your practice follows (commonly at the start of each day and after any maintenance or reagent change).

Plot each control result on a Levey-Jennings chart: a graph with the expected mean at the center and horizontal lines drawn at ±1, ±2, and ±3 standard deviations (SD). Over time, a well-functioning analyzer produces points randomly scattered around the mean. Systematic drift (points trending in one direction) or a point outside ±2 SD on repeated runs signals a problem.

Common Westgard-style rules used in veterinary practice:

• A single point beyond ±3 SD: reject the run immediately.
• Two consecutive points beyond ±2 SD on the same side: reject the run.
• A trend of several consecutive points all above or all below the mean: investigate.

If the analyzer is out of control, stop running patient samples. Possible causes include reagent degradation, temperature fluctuation, dirty cuvettes, or calibration drift. Notify the supervising veterinarian, document the failure on the QC log, and troubleshoot using the operator manual before re-running controls.

Step 4 — Interpreting and Presenting Flagged Values

Your role is not to diagnose — that is the veterinarian's responsibility. Your role is to accurately identify which values fall outside reference intervals, associate them with the correct organ system, and communicate findings clearly.

Azotemic pattern: Elevated BUN and creatinine together indicate azotemia (accumulation of nitrogenous waste). This directs attention to the renal system (and possibly pre-renal causes such as dehydration).

Hepatopathic pattern: Elevated ALT and/or ALP, with decreased albumin or total protein, directs attention to the hepatic (liver) system.

When presenting to the supervising veterinarian, state the finding and the organ system: "BUN and creatinine are both above the upper reference limit for this species; these findings are consistent with azotemia and flag the renal system for your evaluation." Remain objective and factual.

Safety Reminders

• Always wear gloves and follow standard precautions when handling blood samples.
• Never report patient results from an out-of-control analyzer run.
• Label every sample and log sheet with patient ID, date, and time before you begin.
• Discard used needles and tubes in appropriate sharps and biohazard containers.