How to distinguish? The urine HCG assay does not cross-react with these substances, and so, if the patient still makes urine, confirmatory testing with urine HCG is a reasonable first step. In ESKD patients who no longer make urine, progesterone levels can be used as a next step especially when more immediate knowledge of pregnancy status is required. If progesterone is low, viable pregnancy is unlikely, though serial serum HCG levels should be monitored to rule out non-viable pregnancy (egs, ectopic). If there is no urgency to determining pregnancy status, follow-up serum HCG to see if doubling occurs at expected intervals should be performed. In my patient’s case, her serum HCG level one week later was the same as that one week prior, and the serum HCG was deemed to be elevated due to decreased clearance in ESKD.
That cardiac biomarkers, including Troponin and BNP, can be elevated in CKD or ESKD without necessarily having clinical significance is familiar to most of us. Whether you believe that an elevated Troponin in ESKD is due to diminished clearance or some constant low-level myocardial damage of unclear significance, most would be comfortable dismissing borderline positive results without suggestive signs or symptoms.
Recently I was asked an interesting question pertaining to pregnancy testing in CKD and ESKD. A dialysis patient had a serum HCG level that was borderline positive. The patient and her physicians wanted to know whether this could be a false positive related to her kidney disease or whether she may in fact be in the first weeks of a pregnancy. After searching the literature and conferring with my OB colleagues, here is what I found:
Here is a case report and a nice review of the topic. Not surprisingly HCG levels can be falsely elevated in CKD, though for quite a variety of reasons. These include decreased clearance of HCG, increased levels of other gonadotropins that cross react with the HCG assay, including LH and FSH, as well as other cross-reacting substances including cold agglutinins and heterophile antibodies.