Clinical features

• supine tachycardia (pulse > 100 beats/minute)
• supine hypotension (systolic blood pressure < 95 mmHg)
• postural pulse increase of > 30 beats/min or severe dizziness on sitting upright, and if normal then on standing

Severe dizziness and a pulse increase > 30 beats/min on standing make a significant acute bleed more likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected acute blood loss b (pre-test probability: 7.3%)	acute severe blood loss (venesection of 630 to 1150 ml)	postural pulse increase > 30 beats/min or severe postural dizziness on sitting from supine	39	75%	0.22	1.7%
	acute severe blood loss (venesection of 630 to 1150 ml)	postural pulse increase > 30 beats/min or severe postural dizziness on standing from supine	49	79%	0.03	0.24%
	acute moderate blood loss ( venesection of 350 to 600 ml )	postural pulse increase > 30 beats/min or severe postural dizziness on standing from supine	44	78%	0.80	5.9%
	acute severe blood loss ( venesection of 630 to 1150 ml )	supine tachycardia	4.0	24%	0.92	6.8%
	acute severe blood loss ( venesection of 630 to 1150 ml )	supine hypotension	11	46%	0.68	5.1%
	acute moderate blood loss ( venesection of 350 to 600 m )	supine hypotension	4.3	24%	0.90	6.8%

Note:

• Evidence of shock increases the risk of rebleeding or dying ^a
• Postural hypotension (fall in systolic > 20 mmHg on standing) does not usefully diagnose acute blood loss ^b
• Absence of supine tachycardia does not exclude moderate acute blood loss. ^b