Chapter 2 · Common pre-analytical considerations

Key pre-analytical factors in clinical biochemistry: fasting status (glucose, lipids, gastrin), posture (aldosterone, renin), time of collection (cortisol has diurnal variation — morning and afternoon samples differ), sample type (serum vs EDTA vs lithium heparin — some analytes differ significantly), haemolysis (elevates potassium, AST, LDH), lipaemia (interferes with spectrophotometric methods), and icteric samples (bilirubin interferes with some methods).

Chapter 2 · Practical example

eGFR with every creatinine — no exceptions

eGFR must accompany every adult creatinine result. Reporting creatinine without eGFR is clinically incomplete and may delay diagnosis of kidney disease.

▲ The situation

A batch release reveals that three creatinine results have been released without eGFR — a LIS calculation error has prevented eGFR from generating for patients without a previous creatinine on file.

Reference: ISO 15189:2022 Clause 7.5; KDIGO CKD Guidelines

✓
Good practice

The section head holds the three results immediately, contacts the LIS administrator, and has the calculation corrected. The eGFR values are generated: one patient has a creatinine of 132 micromol/L and an eGFR of 48 — CKD Stage 3b, which the clinician would not have identified from the creatinine value alone (132 is above the upper reference interval for females but this is not immediately obvious without clinical context). The result is released with an appropriate comment.

✗
Poor practice

The creatinine results are released without eGFR because the LIS administrator says the calculation fix will take a day. The result of 132 micromol/L is flagged as high, but the clinician, not a nephrologist, does not know that this corresponds to an eGFR of 48 in a 68-year-old woman and does not initiate CKD management.

● What this means for your practice

eGFR is the mandatory interpretive companion to creatinine. A released creatinine without eGFR is incomplete regardless of the technical reason. If the LIS calculation fails, the eGFR must be calculated manually and added to the report before release.