I am wondering what health problems can you detect with just a urine sample ?

Many, for a start:-: Uti if bacteria +/-pus cells present, diabetes if sugar present, suspicion of urinary tract or kidney cancer if blood present: suspect kidney disease if protein present +/-blood, stones w blood, supect liver disease/jaundice if bilirubin present; kidney concentrating problem or hydration from specific gravity: urinary acidity helpful in managing kidney stones: nutrition by presence of ketones: etc.