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Retinopathy of prematurity (ROP) is the major cause of blindness in premature babies, and in the developed world it is a disease of the most immature and unwell infants. Treatment is needed more often in extremely premature babies, taking place in 14% of those born before 26 weeks completed gestation.1 Treatment of severe ROP was originally by cryotherapy, but is now more commonly undertaken with laser, either as transpupillary or trans-scleral diode photocoagulation.
C reactive protein (CRP) is an acute phase protein first discovered in the 1930s. It is a component of the innate immune system. Increased production is thought to be beneficial because of its ability to bind phosphocoline and thus recognise foreign pathogens.2 Tissue damage including burns, trauma, and surgery is known to increase CRP.
Babies undergoing treatment for ROP often have regular CRP measurements to help identify the onset of sepsis. There is currently no evidence as to whether cryotherapy or laser photocoagulation cause a rise in CRP irrespective of sepsis.
To ascertain whether CRP is affected by treatment of ROP, a retrospective case note review of infants treated with laser photocoagulation was undertaken. The notes of 16 infants (11 female and five male) requiring treatment for ROP (mean gestational age 24 weeks and 6 days) were reviewed. Fifteen of the babies received laser photocoagulation by transpupillary diode laser, and one received trans-scleral diode treatment.
CRP concentration before surgery and the first measurement after surgery were obtained. CRP was measured using an automated discretionary discrete analyser (Olympus 600; Olympus Optical Equipment). Units are mg/l.
The time interval between the operation and CRP measurement was 12 hours to 12 days; the median time was three days. CRP concentration before surgery ranged from < 5 to 53 (median < 5). After surgery, the range was < 5–51 (median < 5). The data were non-parametric. A Wilcoxon signed rank test was used to determine whether the null hypothesis (lasering does not alter CRP concentration) was correct. This study did not find a significant difference in CRP concentration after surgery. (Sample size means this study has a 90% power to show significance (p < 0.05) if there were a difference in CRP concentration of 20.)
Our negative findings give some reassurance that if, after treatment for retinopathy, there is concern about infection, a raised CRP concentration is unlikely to be a result of the procedure and more likely to reflect sepsis. However, a prospective study of CRP concentrations after treatment for retinopathy will be necessary to confirm our findings.