During regular blood checkup for my wife high platelet count was observed what does mean? The following are the results (i) PLATELET COUNT 410 X 10³ / μL (ii) PLATELETCRIT (PCT) 0.42 Range : % 0.19 - 0.39 (iii) RED CELL DISTRIBUTION WIDTH - SD (RDW-SD) 5

Normal ranges. Each lab must establish their own normal range for the tests they offer, so there can be some variation between labs. In general, platelets run between 150k-450k/ml These ranges cover 95% of the normal people they test, so 5% of normal people will have values outside the range. The closer a person's values are to the range=more likely normal. Wife's values likely normal for her.
Need more info. All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Having said that, What is her hemoglobin? Iron deficiency is one cause of increase in platelet count. She may wish to take oral iron supplements and multivitamins for about 6 months before repeating the test.
Get it repeated. Platelet count can rise even with exertion. Suggest that you talk to your doctor re. whether it's worth getting another test (make sure she doesn't exert herself for an hour or more prior to the test). I suspect that this will turn out to be normal.