Stabilization of urinary biogenic amines measured in clinical chemistry laboratories

Urinary 5-hydroxyindoleacetic acid (5-HIAA), vanillylmandelic (VMA), homovanillic acid (HVA), catechol-amines and metanephrines are produced in excess by catecholamine-producing tumors. These biogenic amines are unstable at low or high pH and require hydrochloric acid (HCl) to prevent their degradation. However, HCl addition may result in very low pH causing degradation or deconjugation of several metabolites. This study evaluated the buffering properties of sodium citrate to stabilize all biogenic amines. The metabolite concentrations were measured by LC-MS/MS or by a coulometric assay in 22 urine samples collected native and with HCl or sodium citrate. We studied the effect of pH, time (48 h, four weeks) and storage temperature at 22 degrees C, 4 degrees C, and -20 degrees C. We found that catecholamines degradation was prevented by HCl and citrate and that 5-HIAA was degraded in 5 out of 22 samples collected with HCl. All biogenic amines were efficiently stabilized by citrate for four weeks at 22 degrees C, except epinephrine (48 hat 4 degrees C, or four weeks at -20 degrees C). Sodium citrate did not cause quantification or analytical artefacts concerns. In conclusion, sodium citrate is a non-hazardous alternative to HC1 for patients to send unfrozen urine samples to the laboratory which may safely store the sample for four weeks.

Automated summary

This study demonstrates that sodium citrate is an effective alternative to stabilize all biogenic amines’ metabolites, allowing patients to send unfrozen urine samples to the laboratory and safely store them for four weeks.