An expression is derived for the current dependence of spontaneous emission in the lasing state. It shows that the slope of the emission above threshold is controlled by a product of two terms, of which only one is affected by the dynamics of lasing. Since the other depends on subthreshold properties, the slope of the spontaneous characteristic is not a definitive test of laser models. While a rise in spontaneous emission above threshold is inconsistent with the linear rate equations describing the stimulated recombination, a strong saturation is not supportive of them. As an example, comparison of the properties of the laser of Paoli and Barnes, which exhibited a strong saturation, with data on other stripe units with various degrees of saturation shows that the unusually strong saturation they find is caused by an unusually low product of threshold current and external efficiency, not by a different form of the rate equation. As an aside it is shown that the slope ratio also measures the ratio of junction resistances above and below threshold.