A specimen collected at 09:00 and results delta observed in several analytes. Why did this happen?

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Multiple Choice

A specimen collected at 09:00 and results delta observed in several analytes. Why did this happen?

When a specimen is left uncapped, it is exposed to air, allowing gases to exchange. The most important change here is loss of CO2 from the sample, which reduces carbonic acid in solution and raises the pH. That rise in pH shifts the ionization states and stability of many analytes, so several tests can drift together, producing a noticeable delta across multiple results. In practice, this preanalytical error creates a systematic, pH-driven bias rather than a problem confined to a single assay, which is why many analytes change simultaneously. Other scenarios tend to affect results in more limited ways. Delayed centrifugation often alters metabolites and cellular components through ongoing metabolism, but the pattern isn’t driven by a uniform pH shift. Hemolyzed samples mainly release intracellular substances like potassium and LDH, causing spikes in specific tests rather than a broad, pH-linked drift. Expired reagents compromise assay performance in various ways, but the observed multi-analyte changes are best explained by a pH change from exposure to air, which is characteristic of leaving the sample uncapped.

When a specimen is left uncapped, it is exposed to air, allowing gases to exchange. The most important change here is loss of CO2 from the sample, which reduces carbonic acid in solution and raises the pH. That rise in pH shifts the ionization states and stability of many analytes, so several tests can drift together, producing a noticeable delta across multiple results. In practice, this preanalytical error creates a systematic, pH-driven bias rather than a problem confined to a single assay, which is why many analytes change simultaneously.

Other scenarios tend to affect results in more limited ways. Delayed centrifugation often alters metabolites and cellular components through ongoing metabolism, but the pattern isn’t driven by a uniform pH shift. Hemolyzed samples mainly release intracellular substances like potassium and LDH, causing spikes in specific tests rather than a broad, pH-linked drift. Expired reagents compromise assay performance in various ways, but the observed multi-analyte changes are best explained by a pH change from exposure to air, which is characteristic of leaving the sample uncapped.

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