Intra-individual reliability of blood bicarbonate responses and gastrointestinal symptoms following sodium citrate supplementation.

Blood bicarbonate concentration rose significantly over time following sodium citrate ingestion, beginning at 30 minutes in both visits.

• Twelve healthy males (21 ± 1 yr) ingested 0.5 g·kg-1 sodium citrate on two visits 3-7 days apart.
• Capillary [HCO3-] was sampled at baseline and every 30 min up to 240 min.
• The rise from baseline was statistically significant from 30 min onward in both visits (p < 0.001).
• This finding indicates a consistent group-level alkalotic response to sodium citrate supplementation.

Reliability of baseline blood bicarbonate and area under the curve (AUC) was moderate, while peak bicarbonate reliability was poor.

• Baseline [HCO3-] showed moderate reliability: ICC = 0.72 (95% CI: 0.25, 0.91); CV = 3.5%.
• AUC showed moderate reliability: ICC = 0.56; CV = 3.5%.
• Peak [HCO3-] showed poor reliability: ICC = 0.23 (95% CI: -0.29, 0.68); CV = 5.4%.
• Concentration-based indices (baseline and AUC) were identified as more stable measures for monitoring individual responses.

All time-based metrics, including time to peak and time to exceed threshold elevations, demonstrated poor intra-individual reliability.

• Time to peak (TTP) had an ICC = 0.07, typical error (TE) = 49.1 min, and CV = 32.5%.
• Time to exceed +5 mmol·L-1 above baseline and time to exceed +6 mmol·L-1 above baseline also showed poor reliability.
• The large TE of 49.1 min for TTP indicates that the timing of peak bicarbonate is highly variable within individuals across repeated trials.
• These poor time-based reliability values limit the utility of individualized dosing strategies based on a single profiling session.

Monte Carlo simulation showed an ≥80% probability of exceeding +5 mmol·L-1 above baseline between 120 and 240 minutes post-ingestion.

• The probability of exceeding +5 mmol·L-1 ranged from 83.9% to 85.8% across the 120-240 min window.
• The probability of exceeding +6 mmol·L-1 peaked at 69.7% at 150 min.
• These findings support a practical recommendation of a 2-3 hour ingestion window to maximize the probability of achieving a meaningful alkalotic threshold.
• The simulation was used to estimate the probability of exceeding +5 and +6 mmol·L-1 thresholds at each individual time point.

Gastrointestinal symptoms following sodium citrate ingestion were common, unchanged across the two visits, and showed moderate reliability for overall burden.

• GI symptoms were assessed using a 12-item questionnaire recorded concurrently with blood sampling at each visit.
• Overall GI symptom burden was moderately reliable: ICC = 0.61; TE = 2.63; CV = 46.6%.
• GI symptoms did not change significantly between the two visits, indicating a consistent symptom profile across repeated supplementation.
• The high CV of 46.6% for GI burden indicates considerable relative variability despite moderate ICC.

Individual profiling was recommended for athletes requiring precise timing of peak bicarbonate, given the poor reliability of time-based metrics.

• Despite a consistent group-level response, individual timing of peak [HCO3-] was highly variable (TTP CV = 32.5%).
• The authors concluded that concentration-based indices are more stable for monitoring than time-based metrics.
• A 2-3 hour ingestion window was recommended as the practical strategy to maximize the probability of exceeding +5 mmol·L-1.
• Individual profiling was specifically recommended where precise timing relative to competition or exercise is critical.