Final answer:
In the context of postpartum preeclampsia, the significant lab result to report is proteinuria 3+, indicating a potential kidney damage and a hallmark of preeclampsia.
Step-by-step explanation:
The lab result that should be reported to the provider for a postpartum client with preeclampsia is proteinuria 3+. Proteinuria, which refers to high levels of protein in the urine, is a common sign of kidney damage and is especially concerning in the context of preeclampsia. The reference lab values for plasma creatinine are 0.8-1.2 mg/dl for males and 0.6-0.9 mg/dl for females, which means that a creatinine level of 1.2 mg/dL is at the upper limit of normal for males and slightly above normal for females, but the proteinuria is more specific and significant in this clinical context. Hemoglobin of 12 g/dL and a platelet count of 200,000/mm³ are within normal ranges and are not a concern.