Blood test explanation - Acid-base and blood gases

Acid-base and blood gases

If arterial/venous is not specified for a acid-base or blood gas value, then it generally refers to arterial, and not venous which otherwise is standard for other blood tests.

Acid-base and blood gases are among the few blood constituents that exhibit substantial difference between arterial and venous values.^[4] Still, pH, bicarbonate and base excess show a high level of inter-method reliability between arterial and venous tests, so arterial and venous values are roughly equivalent for these.^[35]

Test	Arterial/Venous	Lower limit	Upper limit	Unit	Comments
pH	Arterial	7.34,[7] 7.35[6]	7.44,[7] 7.45[6]
	Venous	7.31[36]	7.41[36]
[H+]	Arterial	36[6]	44[6]	nmol/L
		3.6[37]	4.4[37]	ng/dL
Base excess	Arterial & venous[36]	-3[36]	+3[36]	mEq/L
oxygen pressure (pO2)	Arterial	10,[6] 11[38]	13,[38] 14[6]	kPa
		75,[6][7] 83[15]	100,[7] 105[6]	mmHg or torr
	Venous	4.0[38]	5.3[38]	kPa
		30[36]	40[36]	mmHg or torr
Oxygen saturation	Arterial	94,[36] 95,[10] 96[15]	100[10][15]	%
	Venous	Approximately 75[10]
Carbon dioxide (CO2)	Arterial	4.4,[6] 4.7[38]	5.9,[6] 6.0[38]	kPa	Designated pCO2
		33,[6] 35[7]	44,[6] 45[7]	mmHg or torr
		23[36]	30[36]	mmol/L
		100[39]	132[39]	mg/dL
	Venous	5.5[38]	6.8[38]	kPa
		41[36]	51[36]	mmHg or torr
Bicarbonate (HCO3, )	Arterial & venous	18[15]	23[15]	mmol/L
		110[40]	140[40]	mg/dL
Standard bicarbonate (SBCe)	Arterial & venous	21, 22[6]	27, 28[6]	mmol/L or mEq/L[6]
		134[40]	170[40]	mg/dL