Negative values reflect how much lower a venous sample is expected to be compared to an arterial sample.
In a meta-analysis, Bloom et al. note that there is good correlation between arterial and venous pH and HCO3. They also concluded that despite variability in arterial and venous pCO2 and lactate, normal venous levels have good negative predictive values. 1
Zeserson et al. studied VBG and SaO2 (pulse oximetery) results in critically ill patients. This population included 41% ED, 31% MICU, 27% SICU. 2
Rasheed et al. studied VBG analysis in patients with DKA age 11 and older. 3
Bloom BM, Grundlingh J, Bestwick JP, Harris T. The role of venous blood gas in the emergency department: a systematic review and meta-analysis. Eur J Emerg Med. 2014;21(2):81-8. PubMed
Zeserson E, Goodgame B, Hess JD, et al. Correlation of Venous Blood Gas and Pulse Oximetry With Arterial Blood Gas in the Undifferentiated Critically Ill Patient. J Intensive Care Med. 2016. PubMed
Rasheed JI, Razak MKA, Hussein AAA. The value of venous blood gas analysis in the diagnosis of diabetic ketoacidosis. Diabetes Metab Syndr. 2017;11 Suppl 2:S737-S743. PubMed